feat: multi-instance closures, richer stdlib, and Rust-style diagnostics

Introduce fat function pointers (BuxFn {code, env}) so capturing closures are heap-allocated per value in both bootstrap and selfhost. Expand Array/Map/Set/String/Test/Result APIs, add proper tuple codegen and error snippets with multi-char underlines, golden diagnostic tests, and LSP diagnostics via buxc check.
2026-07-15 16:00:21 +03:00
parent 94e6806dda
commit 61ac06ab5f
48 changed files with 2789 additions and 362 deletions
@@ -3,9 +3,9 @@ SRC := bootstrap/main.nim
 OUT := buxc
 BUILD_DIR := build
-EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator ownership ctfe async concurrency os_time process json iter trait_bounds channel sync jwt
+EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics generics_struct generic_infer generic_infer2 extend_generic pattern_matching strings strings2 map result_option try_operator ownership ctfe async concurrency os_time process json iter trait_bounds channel sync jwt stdlib_ergonomics tuples func_ptr map_remove array_iter_extra string_extra multi_closure
-.PHONY: all build dev debug test clean clean-all test-examples selfhost test-golden selfhost-loop lsp
+.PHONY: all build dev debug test clean clean-all test-examples selfhost test-golden test-errors selfhost-loop lsp
 all: build
@@ -19,7 +19,7 @@ dev:
 debug: dev
 	@echo "Debug binary: buxc_debug"
-test: build test-examples
+test: build test-examples test-errors
 	@echo "Running lexer tests..."
 	$(NIM) c -r tests/lexer_test.nim
 	@echo "Running parser tests..."
@@ -100,6 +100,11 @@ test-golden: build
 	echo "Golden tests: $$passed passed, $$failed failed"; \
 	if [ $$failed -gt 0 ]; then exit 1; fi
 test-errors: build
 	@echo "=== Error diagnostic golden tests ==="
 	@chmod +x tests/error_golden/run.sh
 	@tests/error_golden/run.sh ./$(OUT)
 selfhost-loop: build
 	@echo "=== Selfhost loop: bootstrap determinism check ==="
 	@echo "Build A..."
@@ -128,8 +128,31 @@ proc typeToC*(be: var CBackend, typ: Type): string =
    of "float64": return "double"
    of "bool": return "bool"
    else: return typ.name
-  of tkTuple: return "void*"  # TODO: proper tuple struct
+  of tkTuple:
-  of tkFunc: return "void*"  # TODO: function pointer
+    if typ.inner.len == 0:
      return "Tuple_Empty"
    var parts: seq[string] = @[]
    for e in typ.inner:
      var p = typeToC(be, e)
      p = p.replace("const char*", "cstr").replace("unsigned int", "uint")
      p = p.replace(" ", "_").replace("*", "Ptr").replace("(", "").replace(")", "").replace(",", "_")
      parts.add(p)
    let tname = "Tuple_" & parts.join("_")
    # Ensure typedef is collected alongside slices
    var already = false
    for d in be.sliceTypeDefs:
      if d.name == tname:
        already = true
        break
    if not already:
      # Reuse sliceTypeDefs as a generic "extra typedef" bag: elem holds field list markup
      be.sliceTypeDefs.add((name: tname, elem: "/*tuple*/"))
    return tname
  of tkFunc:
    if typ.inner.len == 0: return "void (*)(void)"
    let params = typ.inner[0..^2].mapIt(typeToC(be, it)).join(", ")
    let ret = typeToC(be, typ.inner[^1])
    return ret & " (*)(" & params & ")"
  else:
    when defined(release):
      return "void*"
@@ -311,10 +334,11 @@ proc emitExpr(be: var CBackend, node: HirNode): string =
      return &"({base}).data[{idx}]"
  of hTupleInit:
-    var elems: seq[string] = @[]
+    let typeName = typeToC(be, node.typ)
-    for e in node.tupleInitElements:
+    var fields: seq[string] = @[]
-      elems.add(be.emitExpr(e))
+    for i, e in node.tupleInitElements:
-    return &"{{{elems.join(\", \")}}}"
+      fields.add(&"._{i} = {be.emitExpr(e)}")
    return &"(({typeName}){{{fields.join(\", \")}}})"
  of hCast:
    let operand = be.emitExpr(node.castOperand)
@@ -1,5 +1,6 @@
 import std/[os, strutils, terminal, strformat, osproc, sets]
 import lexer, parser, ast, sema, manifest, hir_lower, lir_lower, lir_c_backend
 import source_location
 type
  ColorMode* = enum
@@ -89,6 +90,203 @@ proc printInfo(msg: string, useColor: bool) =
  else:
    echo("info: " & msg)
 # ---------------------------------------------------------------------------
 # Rust-style diagnostics (snippet + optional help hint)
 # ---------------------------------------------------------------------------
 proc getSourceLine(path: string, lineNum: uint32): string =
  ## Read a single 1-based line from path. Empty if unavailable.
  if path.len == 0 or lineNum == 0 or not fileExists(path):
    return ""
  try:
    let content = readFile(path)
    var n: uint32 = 1
    for line in content.splitLines():
      if n == lineNum:
        return line
      inc n
  except CatchableError:
    discard
  return ""
 proc extractQuotedName(msg: string): string =
  ## Pull the first 'name' from messages like: undeclared identifier 'foo'
  let a = msg.find('\'')
  if a < 0: return ""
  let b = msg.find('\'', a + 1)
  if b <= a + 1: return ""
  return msg[a + 1 .. b - 1]
 proc underlineLength(lineText: string, col: uint32, message: string): int =
  ## Multi-character underline under the token at `col` (1-based).
  ## Falls back to scanning a source token, or matching a quoted name in the message.
  if lineText.len == 0:
    return 1
  let start = if col > 0: int(col) - 1 else: 0
  if start < 0 or start >= lineText.len:
    return 1
  # Prefer highlighting the quoted identifier/token from the message when it
  # appears on this line (e.g. undeclared identifier 'foo').
  let quoted = extractQuotedName(message)
  if quoted.len > 0:
    let idx = lineText.find(quoted)
    if idx >= 0:
      # If caret is on/near that token, use its full length
      if abs(idx - start) <= quoted.len:
        return quoted.len
  let c0 = lineText[start]
  # String / char / backtick literals
  if c0 == '"' or c0 == '\'' or c0 == '`':
    let quote = c0
    var i = start + 1
    while i < lineText.len:
      if lineText[i] == '\\' and i + 1 < lineText.len:
        i += 2
        continue
      if lineText[i] == quote:
        return i - start + 1
      inc i
    return max(1, lineText.len - start)
  # Identifier or keyword
  if c0.isAlphaAscii or c0 == '_':
    var i = start
    while i < lineText.len and (lineText[i].isAlphaNumeric or lineText[i] == '_'):
      inc i
    return max(1, i - start)
  # Number literal
  if c0.isDigit:
    var i = start
    while i < lineText.len and (lineText[i].isDigit or lineText[i] in {'.', 'x', 'X', 'b', 'B', 'o', 'O', 'a'..'f', 'A'..'F', '_'}):
      inc i
    # optional type suffix: 42i64, 1.0f
    while i < lineText.len and lineText[i] in {'i', 'u', 'f', 'I', 'U', 'F', '0'..'9'}:
      inc i
    return max(1, i - start)
  # Multi-char operators starting at caret
  const multiOps = ["<<=", ">>=", "**", "++", "--", "==", "!=", "<=", ">=",
                    "&&", "||", "<<", ">>", "+=", "-=", "*=", "/=", "%=",
                    "&=", "|=", "^=", "=>", "..", "->"]
  for op in multiOps:
    if start + op.len <= lineText.len and lineText[start .. start + op.len - 1] == op:
      return op.len
  return 1
 proc hintForMessage(msg: string): string =
  ## Actionable help text for common compiler errors.
  let m = msg.toLowerAscii()
  if "cannot assign" in m:
    return "ensure the right-hand side type matches the left-hand side"
  if "undeclared identifier" in m:
    return "check the spelling, or import the symbol from the right module"
  if "too few arguments" in m or "too many arguments" in m:
    return "compare the call with the function's parameter list"
  if "missing argument for parameter" in m:
    return "provide the missing argument (positional or named)"
  if "use of moved value" in m:
    return "the value was moved; clone it or restructure ownership"
  if "shared reference" in m or "checked function" in m:
    return "use '&mut T' for mutation, or drop @[Checked] for unchecked code"
  if "double mutable borrow" in m or "already mutably borrowed" in m:
    return "only one active '&mut' borrow is allowed at a time"
  if "expected expression" in m:
    return "the previous statement may be incomplete (missing value or ';')"
  if "expected type" in m:
    return "write a type name such as 'int', 'String', or 'Array<int>'"
  if "expected field name" in m:
    return "after '.' use an identifier or a tuple index (.0, .1, ...)"
  if "does not implement trait" in m:
    return "add an 'extend Type for Trait { ... }' block, or pick another type"
  if "duplicate symbol" in m:
    return "rename one of the definitions or remove the duplicate"
  if "unterminated" in m:
    return "check for a missing closing quote, backtick, or comment delimiter"
  return ""
 proc printDiagnostic*(severity: string, message: string, loc: SourceLocation,
                      useColor: bool, fallbackFile: string = "") =
  ## Print a Rust-style diagnostic:
  ##   error: message
  ##     --> file:line:col
  ##      |
  ##   42 | source line
  ##      |        ^
  ##      = help: hint
  let isError = severity == "error"
  if useColor:
    stdout.setForegroundColor(if isError: fgRed else: fgYellow)
    stdout.write(severity & ": ")
    stdout.resetAttributes()
    stdout.writeLine(message)
  else:
    let stream = if isError: stderr else: stdout
    stream.writeLine(severity & ": " & message)
  let file = if loc.file.len > 0: loc.file else: fallbackFile
  if loc.line > 0:
    let locStr = if file.len > 0:
      &"{file}:{loc.line}:{loc.column}"
    else:
      &"{loc.line}:{loc.column}"
    if useColor:
      stdout.setForegroundColor(fgCyan)
      stdout.write("  --> ")
      stdout.resetAttributes()
      stdout.writeLine(locStr)
    else:
      stderr.writeLine("  --> " & locStr)
    let lineText = getSourceLine(file, loc.line)
    if lineText.len > 0:
      let gutter = $loc.line
      let pad = " ".repeat(max(gutter.len, 3))
      # If message names a quoted token, prefer caret at that token's start
      var col = loc.column
      let quoted = extractQuotedName(message)
      if quoted.len > 0:
        let idx = lineText.find(quoted)
        if idx >= 0:
          col = uint32(idx + 1)
      let ulen = underlineLength(lineText, col, message)
      stdout.writeLine(pad & " |")
      stdout.writeLine(" " & gutter & " | " & lineText)
      # Multi-char underline under the token (1-based column)
      var caretPad = ""
      if col > 0:
        caretPad = " ".repeat(int(col) - 1)
      let marks = "^".repeat(max(1, ulen))
      stdout.writeLine(pad & " | " & caretPad & marks)
  let hint = hintForMessage(message)
  if hint.len > 0:
    if useColor:
      stdout.setForegroundColor(fgGreen)
      stdout.write("   = help: ")
      stdout.resetAttributes()
      stdout.writeLine(hint)
    else:
      stdout.writeLine("   = help: " & hint)
 proc printLexerDiags(diags: seq[LexerDiagnostic], useColor: bool, fallbackFile = "") =
  for d in diags:
    let sev = if d.severity == ldsError: "error" else: "warning"
    printDiagnostic(sev, d.message, d.loc, useColor, fallbackFile)
 proc printParserDiags(diags: seq[ParserDiagnostic], useColor: bool, fallbackFile = "") =
  for d in diags:
    let sev = if d.severity == pdsError: "error" else: "warning"
    printDiagnostic(sev, d.message, d.loc, useColor, fallbackFile)
 proc printSemaDiags(diags: seq[SemaDiagnostic], useColor: bool, fallbackFile = "") =
  for d in diags:
    let sev = if d.severity == sdsError: "error" else: "warning"
    printDiagnostic(sev, d.message, d.loc, useColor, fallbackFile)
 # ---------------------------------------------------------------------------
 # Commands
 # ---------------------------------------------------------------------------
@@ -304,14 +502,12 @@ proc prepareProject(root: string, useColor: bool, opts: GlobalOptions): (Project
      let lexRes = tokenize(source, path)
      if lexRes.hasErrors:
        printError(&"lex errors in {path}", useColor)
-        for d in lexRes.diagnostics:
+        printLexerDiags(lexRes.diagnostics, useColor, path)
          echo $d
        return (pctx, 1)
      let parseRes = parse(lexRes.tokens, path)
      if parseRes.diagnostics.len > 0:
        printError(&"parse errors in {path}", useColor)
-        for d in parseRes.diagnostics:
+        printParserDiags(parseRes.diagnostics, useColor, path)
          echo &"error: {d.message} at {d.loc}"
        return (pctx, 1)
      for decl in parseRes.module.items:
        if decl.kind == dkModule:
@@ -345,9 +541,7 @@ proc cmdCheck*(args: seq[string], opts: GlobalOptions): int =
  let semaRes = analyze(unifiedModule)
  if semaRes.hasErrors:
    printError("type errors in project", useColor)
-    for d in semaRes.diagnostics:
+    printSemaDiags(semaRes.diagnostics, useColor)
      let sev = if d.severity == sdsError: "error" else: "warning"
      echo &"{sev}: {d.message} at {d.loc}"
    return 1
  if not opts.quiet:
    printInfo("check passed", useColor)
@@ -448,9 +642,7 @@ proc cmdBuild*(args: seq[string], opts: GlobalOptions): int =
  let (semaRes, semaCtx) = analyzeFull(unifiedModule)
  if semaRes.hasErrors:
    printError("type errors in project", useColor)
-    for d in semaRes.diagnostics:
+    printSemaDiags(semaRes.diagnostics, useColor)
      let sev = if d.severity == sdsError: "error" else: "warning"
      echo &"{sev}: {d.message} at {d.loc}"
    return 1
  let hirMod = lowerModule(unifiedModule, semaCtx)
@@ -189,6 +189,10 @@ type
    consts*: seq[tuple[name: string, typ: Type, value: HirNode]]
    interfaces*: seq[tuple[name: string, hasAssocTypes: bool, methods: seq[tuple[name: string, params: seq[Type], ret: Type]]]]
    vtables*: seq[tuple[interfaceName: string, concreteType: string, methodNames: seq[string], hasAssocTypes: bool]]
    ## Named functions used as values → need __adapt_ wrappers for fat-func ABI
    funcAdapters*: seq[tuple[name: string, typ: Type]]
    ## Extra func types seen in locals/closures that need BuxFn_* typedefs
    seenFatTypes*: seq[Type]
 # Constructor helpers
 proc hirLit*(tok: Token, typ: Type, loc: SourceLocation): HirNode =
@@ -1,4 +1,4 @@
-import std/[tables, sets, strutils]
+import std/[tables, sets, strutils, strformat]
 import ast, types, token, source_location, hir, sema, scope
 type
@@ -25,6 +25,11 @@ type
    closureDepth*: int
    currentClosureExpr*: Expr
    envInstanceName*: string
    ## Named functions that must be wrapped as fat func values (multi-instance ABI)
    funcAdapters*: HashSet[string]
    funcAdapterSigs*: Table[string, Type]
    ## All func types that need BuxFn_* typedefs (including locals)
    seenFatTypes*: seq[Type]
 proc freshName(ctx: var LowerCtx): string =
  inc ctx.varCounter
@@ -159,6 +164,50 @@ proc initLowerCtx*(module: Module, sema: Sema): LowerCtx =
  result.generatedFuncInsts = initTable[string, bool]()
  result.extraFuncs = @[]
  result.varTypeExprs = initTable[string, TypeExpr]()
  result.funcAdapters = initHashSet[string]()
  result.funcAdapterSigs = initTable[string, Type]()
  result.seenFatTypes = @[]
 proc sanitizeFatPart(s: string): string =
  result = s.replace("const char*", "cstr").replace("unsigned int", "uint")
  result = result.replace(" ", "_").replace("*", "Ptr").replace("(", "").replace(")", "").replace(",", "_").replace(".", "_")
 proc typeNameForFat(typ: Type): string
 proc hirFuncFatTypeName*(typ: Type): string
 proc typeNameForFat(typ: Type): string =
  ## Lightweight C-ish name for fat-func mangling (mirrors lir typeToCStr subset).
  if typ == nil: return "void"
  case typ.kind
  of tkVoid: return "void"
  of tkBool, tkBool8, tkBool16, tkBool32: return "bool"
  of tkStr: return "cstr"
  of tkInt, tkInt8, tkInt16, tkInt32, tkInt64: return "int"
  of tkUInt, tkUInt8, tkUInt16, tkUInt32, tkUInt64: return "uint"
  of tkFloat32: return "float"
  of tkFloat64: return "double"
  of tkPointer, tkRef, tkMutRef:
    if typ.inner.len > 0: return sanitizeFatPart(typeNameForFat(typ.inner[0]) & "Ptr")
    return "voidPtr"
  of tkNamed:
    case typ.name
    of "String", "str": return "cstr"
    else: return sanitizeFatPart(typ.name)
  of tkFunc:
    return hirFuncFatTypeName(typ)
  else:
    return "int"
 proc hirFuncFatTypeName*(typ: Type): string =
  if typ == nil or typ.kind != tkFunc: return "BuxFn_void"
  let ret = if typ.inner.len > 0: typeNameForFat(typ.inner[^1]) else: "void"
  var parts: seq[string] = @[sanitizeFatPart(ret)]
  if typ.inner.len > 1:
    for p in typ.inner[0 ..^ 2]:
      parts.add(sanitizeFatPart(typeNameForFat(p)))
  else:
    parts.add("void")
  return "BuxFn_" & parts.join("_")
 proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type
@@ -291,7 +340,14 @@ proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type =
  of tekOwn: return ctx.resolveTypeExpr(te.pointerPointee)
  of tekDynRef: return makeDynRef(te.dynInterface)
  of tekPointer: return makePointer(ctx.resolveTypeExpr(te.pointerPointee))
  of tekRef: return makeRef(ctx.resolveTypeExpr(te.pointerPointee))
  of tekMutRef: return makeMutRef(ctx.resolveTypeExpr(te.pointerPointee))
  of tekSlice: return makeSlice(ctx.resolveTypeExpr(te.sliceElement))
  of tekTuple:
    var elems: seq[Type] = @[]
    for e in te.tupleElements:
      elems.add(ctx.resolveTypeExpr(e))
    return makeTuple(elems)
  of tekFunc:
    var params: seq[Type] = @[]
    for p in te.funcParams:
@@ -523,6 +579,18 @@ proc resolveExprType(ctx: var LowerCtx, expr: Expr): Type =
    return makeVoid()
  of ekBorrow:
    return ctx.resolveExprType(expr.exprBorrowOperand)
  of ekClosure:
    var params: seq[Type] = @[]
    for p in expr.exprClosureParams:
      if p.ptype != nil:
        params.add(ctx.resolveTypeExpr(p.ptype))
      else:
        params.add(makeUnknown())
    let ret = if expr.exprClosureReturnType != nil:
      ctx.resolveTypeExpr(expr.exprClosureReturnType)
    else:
      makeVoid()
    return makeFunc(params, ret)
  else: return makeUnknown()
 proc extractGenericStructInfo(ctx: LowerCtx, te: TypeExpr): tuple[baseName: string, typeArgs: seq[TypeExpr]] =
@@ -742,9 +810,26 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
        let capType = if idx < ctx.currentClosureExpr.captureTypeKinds.len: Type(kind: TypeKind(ctx.currentClosureExpr.captureTypeKinds[idx])) else: makeInt()
        let base = hirVar(ctx.envInstanceName, makeNamed(""), loc)
        return HirNode(kind: hFieldAccess, fieldAccessName: name, fieldAccessBase: base, typ: capType, loc: loc)
    var resolvedName = name
    if ctx.importTable.hasKey(name):
-      return hirVar(ctx.importTable[name], typ, loc)
+      resolvedName = ctx.importTable[name]
-    return hirVar(name, typ, loc)
+    # Named function used as a value → fat function pointer via adapter
    if typ != nil and typ.kind == tkFunc:
      let sym = ctx.globalScope.lookup(name)
      let sym2 = if sym == nil: ctx.globalScope.lookup(resolvedName) else: sym
      if sym2 != nil and sym2.kind == skFunc:
        let adaptName = "__adapt_" & resolvedName
        ctx.funcAdapters.incl(resolvedName)
        ctx.funcAdapterSigs[resolvedName] = typ
        let fatName = hirFuncFatTypeName(typ)
        let nullEnv = HirNode(kind: hCast,
          castOperand: hirLit(Token(kind: tkIntLiteral, text: "0", loc: loc), makeInt(), loc),
          castType: makePointer(makeVoid()), typ: makePointer(makeVoid()), loc: loc)
        return HirNode(kind: hStructInit, structInitName: fatName, structInitFields: @[
          (name: "code", value: hirVar(adaptName, makePointer(makeVoid()), loc)),
          (name: "env", value: nullEnv)
        ], typ: typ, loc: loc)
    return hirVar(resolvedName, typ, loc)
  of ekPath:
    # Handle enum variants: Color::Red → Color_Red
@@ -756,6 +841,32 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
    return hirSelf(typ, loc)
  of ekUnary:
    # &NamedFunc used as func value → fat adapter (not a raw C function pointer)
    if expr.exprUnaryOp == tkAmp and expr.exprUnaryOperand != nil and
       expr.exprUnaryOperand.kind == ekIdent:
      let fname = expr.exprUnaryOperand.exprIdent
      var resolved = fname
      if ctx.importTable.hasKey(fname):
        resolved = ctx.importTable[fname]
      let sym = ctx.globalScope.lookup(resolved)
      if sym != nil and sym.kind == skFunc:
        # Prefer declared func type on the symbol; fall back to expression type
        var ftyp = if sym.typ != nil and sym.typ.kind == tkFunc: sym.typ else: typ
        if ftyp == nil or ftyp.kind != tkFunc:
          ftyp = ctx.resolveExprType(expr.exprUnaryOperand)
        if ftyp != nil and ftyp.kind == tkFunc:
          let adaptName = "__adapt_" & resolved
          ctx.funcAdapters.incl(resolved)
          ctx.funcAdapterSigs[resolved] = ftyp
          ctx.seenFatTypes.add(ftyp)
          let fatName = hirFuncFatTypeName(ftyp)
          let nullEnv = HirNode(kind: hCast,
            castOperand: hirLit(Token(kind: tkIntLiteral, text: "0", loc: loc), makeInt(), loc),
            castType: makePointer(makeVoid()), typ: makePointer(makeVoid()), loc: loc)
          return HirNode(kind: hStructInit, structInitName: fatName, structInitFields: @[
            (name: "code", value: hirVar(adaptName, makePointer(makeVoid()), loc)),
            (name: "env", value: nullEnv)
          ], typ: ftyp, loc: loc)
    let operand = ctx.lowerExpr(expr.exprUnaryOperand)
    return hirUnary(expr.exprUnaryOp, operand, typ, loc)
@@ -883,6 +994,16 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
      calleeName = expr.exprCallCallee.exprPath.join("_")
    let args = ctx.lowerCallArgs(expr.exprCallCallee, expr.exprCallArgs)
    if calleeName != "":
      # Named global function → direct call
      let sym = ctx.globalScope.lookup(calleeName)
      if sym != nil and sym.kind == skFunc:
        return hirCall(calleeName, args, typ, loc)
      # Variable holding a fat function pointer → indirect call
      let ct = ctx.resolveExprType(expr.exprCallCallee)
      if ct != nil and ct.kind == tkFunc:
        let callee = hirVar(calleeName, ct, loc)
        return HirNode(kind: hCallIndirect, callIndirectCallee: callee,
                       callIndirectArgs: args, typ: typ, loc: loc)
      return hirCall(calleeName, args, typ, loc)
    else:
      let callee = ctx.lowerExpr(expr.exprCallCallee)
@@ -1236,7 +1357,32 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
  of ekClosure:
    let f = ctx.lowerClosureFunc(expr)
-    return hirUnary(tkAmp, hirVar(f.name, makeFunc(@[], makeVoid()), loc), typ, loc)
+    if typ != nil and typ.kind == tkFunc:
      ctx.seenFatTypes.add(typ)
    let fatName = hirFuncFatTypeName(typ)
    if expr.captureCount > 0 and f.envStructName.len > 0:
      # Heap-allocate a fresh env so each closure value is independent
      let envTmp = "__envp_" & $ctx.varCounter
      inc ctx.varCounter
      let fatTmp = "__fat_" & $ctx.varCounter
      inc ctx.varCounter
      var code = ""
      code.add(&"{f.envStructName}* {envTmp} = ({f.envStructName}*)bux_alloc(sizeof({f.envStructName}));\n")
      for i in 0 ..< expr.captureCount:
        let capName = expr.captureNames[i]
        code.add(&"{envTmp}->{capName} = {capName};\n")
      code.add(&"{fatName} {fatTmp} = {{ .code = {f.name}, .env = {envTmp} }};")
      ctx.pendingStmts.add(HirNode(kind: hEmit, emitCode: code, typ: makeVoid(), loc: loc))
      return hirVar(fatTmp, typ, loc)
    else:
      # Capture-less: fat pointer with NULL env
      let nullEnv = HirNode(kind: hCast,
        castOperand: hirLit(Token(kind: tkIntLiteral, text: "0", loc: loc), makeInt(), loc),
        castType: makePointer(makeVoid()), typ: makePointer(makeVoid()), loc: loc)
      return HirNode(kind: hStructInit, structInitName: fatName, structInitFields: @[
        (name: "code", value: hirVar(f.name, makePointer(makeVoid()), loc)),
        (name: "env", value: nullEnv)
      ], typ: typ, loc: loc)
  else:
    return HirNode(kind: hLit, litToken: Token(kind: tkIntLiteral, text: "0", loc: loc),
@@ -1255,28 +1401,14 @@ proc lowerStmt(ctx: var LowerCtx, stmt: Stmt): HirNode =
    if stmt.stmtLetInit != nil:
      initHir = ctx.lowerExpr(stmt.stmtLetInit)
    let allocaType = if stmt.stmtLetType != nil:
-      case stmt.stmtLetType.kind
+      # Full resolve covers named, pointer, slice, tuple, func, refs, etc.
-      of tekNamed:
+      ctx.resolveTypeExpr(stmt.stmtLetType)
        ctx.resolveTypeExpr(stmt.stmtLetType)
      of tekOwn:
        ctx.resolveTypeExpr(stmt.stmtLetType.pointerPointee)
      of tekPointer:
        let pointeeType = ctx.resolveTypeExpr(stmt.stmtLetType.pointerPointee)
        makePointer(pointeeType)
      of tekSlice:
        let elemType = ctx.resolveTypeExpr(stmt.stmtLetType.sliceElement)
        makeSlice(elemType)
      of tekFunc:
        var params: seq[Type] = @[]
        for p in stmt.stmtLetType.funcParams:
          params.add(ctx.resolveTypeExpr(p))
        let ret = if stmt.stmtLetType.funcRet != nil: ctx.resolveTypeExpr(stmt.stmtLetType.funcRet) else: makeVoid()
        makeFunc(params, ret)
      else: makeUnknown()
    elif stmt.stmtLetInit != nil:
      ctx.resolveExprType(stmt.stmtLetInit)
    else:
      makeUnknown()
    if allocaType != nil and allocaType.kind == tkFunc:
      ctx.seenFatTypes.add(allocaType)
    let alloca = hirAlloca(stmt.stmtLetName, allocaType, loc)
    let varNode = hirVar(stmt.stmtLetName, makePointer(allocaType), loc)
@@ -1296,22 +1428,7 @@ proc lowerStmt(ctx: var LowerCtx, stmt: Stmt): HirNode =
    if initHir != nil:
      let store = hirStore(varNode, initHir, loc)
      stmts.add(store)
-    # If init is a closure with captures, emit capture assignments
+    # Capture filling for closures is done at the ekClosure site (heap env).
    if stmt.stmtLetInit != nil and stmt.stmtLetInit.kind == ekClosure and stmt.stmtLetInit.captureCount > 0:
      let closureIdx = ctx.varCounter - 1
      let envInst = "__closure_env_instance_" & $closureIdx
      var capStmts: seq[HirNode] = @[]
      for i in 0 ..< stmt.stmtLetInit.captureCount:
        let capName = stmt.stmtLetInit.captureNames[i]
        let capType = if i < stmt.stmtLetInit.captureTypeKinds.len: Type(kind: TypeKind(stmt.stmtLetInit.captureTypeKinds[i])) else: makeInt()
        let base = hirVar(envInst, makeNamed(""), loc)
        let field = HirNode(kind: hFieldAccess, fieldAccessName: capName, fieldAccessBase: base, typ: capType, loc: loc)
        let val = hirVar(capName, capType, loc)
        capStmts.add(hirAssign(field, val, loc))
      # Prepend capture assignments before the let
      var allStmts = capStmts
      allStmts.add(stmts)
      return hirBlock(allStmts, nil, makeVoid(), loc)
    return hirBlock(stmts, nil, makeVoid(), loc)
  of skReturn:
@@ -1723,6 +1840,8 @@ proc lowerClosureFunc(ctx: var LowerCtx, expr: Expr): HirFunc =
  let name = "__closure_" & $ctx.varCounter
  inc ctx.varCounter
  var f = HirFunc(name: name, isPublic: false)
  # Always take a leading env pointer (fat-func ABI); may be unused.
  f.params.add((name: "__env", typ: makePointer(makeVoid())))
  # Copy capture metadata
  if expr.captureCount > 0:
    f.captureNames = expr.captureNames
@@ -1730,7 +1849,7 @@ proc lowerClosureFunc(ctx: var LowerCtx, expr: Expr): HirFunc =
      f.captureTypes.add(Type(kind: TypeKind(tk)))
    f.envStructName = "__closure_env_" & $(ctx.varCounter - 1)
    f.envInstanceName = "__closure_env_instance_" & $(ctx.varCounter - 1)
-  # Params
+  # User params
  for p in expr.exprClosureParams:
    f.params.add((name: p.name, typ: if p.ptype != nil: ctx.resolveTypeExpr(p.ptype) else: makeUnknown()))
  # Return type
@@ -1935,4 +2054,8 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
      if allFound:
        vtableInfos.add((ifaceName, typeName, methodNames, hasAssoc))
-  result = HirModule(funcs: funcs, externFuncs: externFuncs, structs: structs, enums: enums, consts: consts, interfaces: ifaceInfos, vtables: vtableInfos)
+  var adapters: seq[tuple[name: string, typ: Type]] = @[]
  for name in ctx.funcAdapters:
    let t = if ctx.funcAdapterSigs.hasKey(name): ctx.funcAdapterSigs[name] else: makeFunc(@[makeInt()], makeInt())
    adapters.add((name, t))
  result = HirModule(funcs: funcs, externFuncs: externFuncs, structs: structs, enums: enums, consts: consts, interfaces: ifaceInfos, vtables: vtableInfos, funcAdapters: adapters, seenFatTypes: ctx.seenFatTypes)
@@ -70,7 +70,8 @@ proc matchStr(lex: var Lexer, s: string): bool =
  return true
 proc currentLocation(lex: Lexer): SourceLocation =
-  result = SourceLocation(line: lex.line, column: lex.col, offset: uint32(lex.pos))
+  result = SourceLocation(line: lex.line, column: lex.col, offset: uint32(lex.pos),
                          file: lex.sourceName)
 proc emitError(lex: var Lexer, loc: SourceLocation, message: string) =
  lex.diagnostics.add(LexerDiagnostic(severity: ldsError, loc: loc, message: message))
@@ -149,14 +149,22 @@ proc emitInstr(be: var LirCBackend, instr: LirInstr) =
    be.emitLine(&"{v(instr.src)}({argsStr});")
  of lirCallIndirect:
    ## Fat function pointer call: f.code(f.env, args...)
    var argsStr = ""
    for i, arg in instr.extra:
      if i > 0: argsStr.add(", ")
      argsStr.add(v(arg))
    let callee = v(instr.src)
    if instr.dst.kind != lvkVoid:
-      be.emitLine(&"{v(instr.dst)} = ({v(instr.src)})({argsStr});")
+      if argsStr.len > 0:
        be.emitLine(&"{v(instr.dst)} = ({callee}.code)({callee}.env, {argsStr});")
      else:
        be.emitLine(&"{v(instr.dst)} = ({callee}.code)({callee}.env);")
    else:
-      be.emitLine(&"({v(instr.src)})({argsStr});")
+      if argsStr.len > 0:
        be.emitLine(&"({callee}.code)({callee}.env, {argsStr});")
      else:
        be.emitLine(&"({callee}.code)({callee}.env);")
  # ── Return ──
  of lirRet:
@@ -348,6 +356,21 @@ proc emitFunc(be: var LirCBackend, f: LirFunc, funcRetTypes: Table[string, strin
 # ── Struct/Enum emission (from HIR module) ──
 proc sanitizeCTypeNamePart(s: string): string =
  result = s
  result = result.replace("const char*", "cstr")
  result = result.replace("unsigned int", "uint")
  result = result.replace(" ", "_")
  result = result.replace("*", "Ptr")
  result = result.replace("(", "")
  result = result.replace(")", "")
  result = result.replace(",", "_")
  result = result.replace(".", "_")
 proc typeToCStr(typ: Type): string
 proc funcFatTypeName(typ: Type): string
 proc funcCodePtrType(typ: Type): string
 proc typeToCStr(typ: Type): string =
  ## Duplicate from lir_lower for self-containedness
  if typ == nil: return "int"
@@ -396,13 +419,39 @@ proc typeToCStr(typ: Type): string =
    of "float64": return "double"
    of "bool": return "bool"
    else: return typ.name
  of tkTuple:
    if typ.inner.len == 0:
      return "Tuple_Empty"
    var parts: seq[string] = @[]
    for e in typ.inner:
      parts.add(sanitizeCTypeNamePart(typeToCStr(e)))
    return "Tuple_" & parts.join("_")
  of tkFunc:
-    if typ.inner.len == 0: return "void (*)(void)"
+    return funcFatTypeName(typ)
    let params = typ.inner[0..^2].mapIt(typeToCStr(it)).join(", ")
    let ret = typeToCStr(typ.inner[^1])
    return ret & " (*)(" & params & ")"
  else: return "int"
 proc funcFatTypeName(typ: Type): string =
  if typ == nil or typ.kind != tkFunc:
    return "BuxFn_void"
  let ret = if typ.inner.len > 0: typeToCStr(typ.inner[^1]) else: "void"
  var parts: seq[string] = @[sanitizeCTypeNamePart(ret)]
  if typ.inner.len > 1:
    for p in typ.inner[0 ..^ 2]:
      parts.add(sanitizeCTypeNamePart(typeToCStr(p)))
  else:
    parts.add("void")
  return "BuxFn_" & parts.join("_")
 proc funcCodePtrType(typ: Type): string =
  if typ == nil or typ.kind != tkFunc:
    return "void (*)(void*)"
  let ret = if typ.inner.len > 0: typeToCStr(typ.inner[^1]) else: "void"
  var params: seq[string] = @["void* env"]
  if typ.inner.len > 1:
    for p in typ.inner[0 ..^ 2]:
      params.add(typeToCStr(p))
  return ret & " (*)(" & params.join(", ") & ")"
 proc emitStructDef(be: var LirCBackend, name: string, fields: seq[tuple[name: string, typ: Type]]) =
  be.emitLine(&"typedef struct {name} {{")
  be.indent += 1
@@ -481,11 +530,36 @@ proc collectValueDeps(typ: Type): seq[string] =
    return @[typ.name]
  of tkSlice:
    return @[typeToCStr(typ)]
-  of tkPointer, tkRef, tkMutRef, tkTuple, tkFunc:
+  of tkTuple:
    var deps: seq[string] = @[]
    for e in typ.inner:
      for d in collectValueDeps(e):
        if d notin deps:
          deps.add(d)
      if e != nil and e.kind == tkTuple:
        let tn = typeToCStr(e)
        if tn notin deps:
          deps.add(tn)
    return deps
  of tkPointer, tkRef, tkMutRef, tkFunc:
    return @[]
  else:
    return @[]
 proc emitTupleDef(be: var LirCBackend, typ: Type) =
  ## typedef struct { T0 _0; T1 _1; ... } Tuple_...;
  let name = typeToCStr(typ)
  be.emitLine(&"typedef struct {name} {{")
  be.indent += 1
  if typ.inner.len == 0:
    be.emitLine("char _pad;")
  else:
    for i, e in typ.inner:
      be.emitLine(&"{typeToCStr(e)} _{i};")
  be.indent -= 1
  be.emitLine(&"}} {name};")
  be.emitLine("")
 proc emitSliceTypeDef(be: var LirCBackend, name: string, elem: string) =
  be.emitLine(&"typedef struct {{ {elem}* data; size_t len; }} {name};")
@@ -663,6 +737,104 @@ proc emitModule*(be: var LirCBackend, builder: LirBuilder, module: HirModule): s
    elif sliceMap.hasKey(name):
      be.emitSliceTypeDef(name, sliceMap[name])
  # Collect and emit tuple typedefs used in the module (and nested tuples first).
  var tupleTypes: seq[Type] = @[]
  var tupleNames: HashSet[string]
  proc registerTuple(t: Type) =
    if t == nil: return
    case t.kind
    of tkTuple:
      for e in t.inner:
        registerTuple(e)
      let name = typeToCStr(t)
      if not tupleNames.contains(name):
        tupleNames.incl(name)
        tupleTypes.add(t)
    of tkPointer, tkRef, tkMutRef, tkSlice:
      if t.inner.len > 0:
        registerTuple(t.inner[0])
    of tkFunc:
      for e in t.inner:
        registerTuple(e)
    else:
      discard
  for f in module.funcs:
    registerTuple(f.retType)
    for p in f.params:
      registerTuple(p.typ)
  for ef in module.externFuncs:
    registerTuple(ef.retType)
    for p in ef.params:
      registerTuple(p.typ)
  for s in module.structs:
    for f in s.fields:
      registerTuple(f.typ)
  for e in module.enums:
    for v in e.variants:
      for ft in v.fields:
        registerTuple(ft)
      for nf in v.namedFields:
        registerTuple(nf.typ)
  if tupleTypes.len > 0:
    be.emitLine("/* Tuple types */")
    for tt in tupleTypes:
      be.emitTupleDef(tt)
  # Fat function-pointer typedefs (BuxFn_*) — before forward decls that use them
  var fatTypes: seq[Type] = @[]
  var fatNames: HashSet[string]
  proc registerFat(t: Type) =
    if t == nil: return
    case t.kind
    of tkFunc:
      for e in t.inner: registerFat(e)
      let n = funcFatTypeName(t)
      if not fatNames.contains(n):
        fatNames.incl(n)
        fatTypes.add(t)
    of tkPointer, tkRef, tkMutRef, tkSlice:
      if t.inner.len > 0: registerFat(t.inner[0])
    of tkTuple:
      for e in t.inner: registerFat(e)
    else: discard
  for f in module.funcs:
    registerFat(f.retType)
    for p in f.params: registerFat(p.typ)
  for ef in module.externFuncs:
    registerFat(ef.retType)
    for p in ef.params: registerFat(p.typ)
  for a in module.funcAdapters:
    registerFat(a.typ)
  for t in module.seenFatTypes:
    registerFat(t)
  if fatTypes.len > 0:
    be.emitLine("/* Fat function pointer types (code + env) */")
    for ft in fatTypes:
      let n = funcFatTypeName(ft)
      let codeT = funcCodePtrType(ft)
      be.emitLine(&"typedef struct {n} {{")
      be.indent += 1
      be.emitLine(cParamDecl(codeT, "code") & ";")
      be.emitLine("void* env;")
      be.indent -= 1
      be.emitLine(&"}} {n};")
      be.emitLine("")
  # Env structs for closures with captures (heap-allocated per value)
  for f in module.funcs:
    if f.captureNames.len > 0 and f.envStructName != "":
      be.emitLine(&"typedef struct {f.envStructName} {{")
      be.indent += 1
      for i in 0 ..< f.captureNames.len:
        let capName = f.captureNames[i]
        let capType = if i < f.captureTypes.len: typeToCStr(f.captureTypes[i]) else: "int"
        be.emitLine(&"{capType} {capName};")
      be.indent -= 1
      be.emitLine(&"}} {f.envStructName};")
      be.emitLine("")
  # Forward function declarations
  for f in module.funcs:
    let rt = typeToCStr(f.retType)
@@ -707,18 +879,28 @@ proc emitModule*(be: var LirCBackend, builder: LirBuilder, module: HirModule): s
    be.emitLine("};")
    be.emitLine("")
-  # Emit env structs for closures with captures
+  # Adapters for named functions used as fat-func values (after forward decls)
-  for f in module.funcs:
+  if module.funcAdapters.len > 0:
-    if f.captureNames.len > 0 and f.envStructName != "":
+    be.emitLine("/* Fat-func adapters for named functions */")
-      be.emitLine(&"struct {f.envStructName} {{")
+    for a in module.funcAdapters:
      let ret = if a.typ.inner.len > 0: typeToCStr(a.typ.inner[^1]) else: "void"
      var params: seq[string] = @["void* env"]
      var argNames: seq[string] = @[]
      if a.typ.inner.len > 1:
        for i, p in a.typ.inner[0 ..^ 2]:
          let pn = "a" & $i
          params.add(typeToCStr(p) & " " & pn)
          argNames.add(pn)
      let argsStr = argNames.join(", ")
      be.emitLine(&"static {ret} __adapt_{a.name}({params.join(\", \")}) {{")
      be.indent += 1
-      for i in 0 ..< f.captureNames.len:
+      be.emitLine("(void)env;")
-        let capName = f.captureNames[i]
+      if ret == "void":
-        let capType = if i < f.captureTypes.len: typeToCStr(f.captureTypes[i]) else: "int"
+        be.emitLine(&"{a.name}({argsStr});")
-        be.emitLine(&"{capType} {capName};")
+      else:
        be.emitLine(&"return {a.name}({argsStr});")
      be.indent -= 1
-      be.emitLine("};")
+      be.emitLine("}")
      be.emitLine(&"static struct {f.envStructName} {f.envInstanceName};")
      be.emitLine("")
  # Emit all LIR functions
@@ -57,6 +57,22 @@ proc cEscape(s: string): string =
    of '\0': result.add("\\0")
    else: result.add(c)
 proc sanitizeCTypeNamePart(s: string): string =
  ## Make a C type string safe for use inside a typedef name.
  result = s
  result = result.replace("const char*", "cstr")
  result = result.replace("unsigned int", "uint")
  result = result.replace(" ", "_")
  result = result.replace("*", "Ptr")
  result = result.replace("(", "")
  result = result.replace(")", "")
  result = result.replace(",", "_")
  result = result.replace(".", "_")
 proc typeToCStr(typ: Type): string
 proc funcFatTypeName*(typ: Type): string
 proc funcCodePtrType*(typ: Type): string
 proc typeToCStr(typ: Type): string =
  ## Convert a Bux Type to a C type string.
  if typ == nil: return "int"
@@ -105,13 +121,44 @@ proc typeToCStr(typ: Type): string =
    of "float64": return "double"
    of "bool": return "bool"
    else: return typ.name
  of tkTuple:
    ## (T, U) → typedef struct { T _0; U _1; } Tuple_T_U;
    if typ.inner.len == 0:
      return "Tuple_Empty"
    var parts: seq[string] = @[]
    for e in typ.inner:
      parts.add(sanitizeCTypeNamePart(typeToCStr(e)))
    return "Tuple_" & parts.join("_")
  of tkFunc:
-    if typ.inner.len == 0: return "void (*)(void)"
+    ## Fat function pointer: { code(env, args...), env }
-    let params = typ.inner[0..^2].mapIt(typeToCStr(it)).join(", ")
+    ## Enables multi-instance closures with captures.
-    let ret = typeToCStr(typ.inner[^1])
+    return funcFatTypeName(typ)
    return ret & " (*)(" & params & ")"
  else: return "int"
 proc funcFatTypeName*(typ: Type): string =
  ## BuxFn_<ret>_<params...>  (sanitized)
  if typ == nil or typ.kind != tkFunc:
    return "BuxFn_void"
  let ret = if typ.inner.len > 0: typeToCStr(typ.inner[^1]) else: "void"
  var parts: seq[string] = @[sanitizeCTypeNamePart(ret)]
  if typ.inner.len > 1:
    for p in typ.inner[0 ..^ 2]:
      parts.add(sanitizeCTypeNamePart(typeToCStr(p)))
  else:
    parts.add("void")
  return "BuxFn_" & parts.join("_")
 proc funcCodePtrType*(typ: Type): string =
  ## C type of the .code field: ret (*)(void* env, params...)
  if typ == nil or typ.kind != tkFunc:
    return "void (*)(void*)"
  let ret = if typ.inner.len > 0: typeToCStr(typ.inner[^1]) else: "void"
  var params: seq[string] = @["void* env"]
  if typ.inner.len > 1:
    for i, p in typ.inner[0 ..^ 2]:
      params.add(typeToCStr(p))
  return ret & " (*)(" & params.join(", ") & ")"
 proc hirTypeToC(ctx: var LowerToLirCtx, node: HirNode): string =
  if node == nil: return "int"
  result = typeToCStr(node.typ)
@@ -498,7 +545,12 @@ proc lowerExpr(ctx: var LowerToLirCtx, node: HirNode): LirValue =
    for e in node.tupleInitElements:
      elems.add(lowerExpr(ctx, e))
    let t = b.freshTemp()
-    b.emitRawC(&"/* tuple */ {t.strVal} = {{{elems.mapIt($it).join(\", \")}}};")
+    let typeName = typeToCStr(node.typ)
    b.emitAlloca(t.strVal, typeName)
    var fields: seq[string] = @[]
    for i, e in elems:
      fields.add(&"._{i} = {lirValToC(e)}")
    b.emitRawC(&"{t.strVal} = ({typeName}){{{fields.join(\", \")}}};")
    return t
  # ── If expression (ternary) ──
@@ -780,6 +832,13 @@ proc lowerModuleToLir*(hirMod: HirModule): LirBuilder =
    ctx.funcRetType = retCT
    ctx.builder.beginFunc(f.name, params, retCT, f.isPublic)
    # Closure thunks: materialize env from fat-func env pointer (by-value copy)
    if f.captureNames.len > 0 and f.envStructName.len > 0 and f.envInstanceName.len > 0:
      ctx.builder.emitRawC(&"struct {f.envStructName} {f.envInstanceName} = *((struct {f.envStructName}*)__env);")
    elif f.params.len > 0 and f.params[0].name == "__env":
      # Capture-less closure thunk still receives env
      ctx.builder.emitRawC("(void)__env;")
    if f.body != nil:
      if f.body.kind == hBlock:
        for stmt in f.body.blockStmts:
@@ -660,11 +660,15 @@ proc parsePostfix(p: var Parser): Expr =
      discard p.expect(tkRBracket, "expected ']' to close index")
      left = Expr(kind: ekIndex, loc: loc, exprIndexObj: left, exprIndexIdx: idx, exprIndexBoundsCheck: false)
    of tkDot:
-      # Field expression or .await
+      # Field expression, tuple index (.0, .1), or .await
      discard p.advance()
      if p.check(tkAwait):
        discard p.advance()
        left = Expr(kind: ekAwait, loc: loc, exprAwaitOperand: left)
      elif p.check(tkIntLiteral):
        # Tuple element access: t.0 → field "_0"
        let idxText = p.advance().text
        left = Expr(kind: ekField, loc: loc, exprFieldObj: left, exprFieldName: "_" & idxText)
      else:
        let fieldName = p.expectIdentOrKeyword("expected field name after '.'").text
        left = Expr(kind: ekField, loc: loc, exprFieldObj: left, exprFieldName: fieldName)
@@ -1249,6 +1249,20 @@ proc checkExpr(sema: var Sema, expr: Expr, scope: Scope): Type =
    # Auto-dereference pointer/reference types for field access
    if objType.kind in {tkPointer, tkRef, tkMutRef} and objType.inner.len > 0:
      objType = objType.inner[0]
    if objType.kind == tkTuple:
      # Tuple fields: .0 / .1 → stored as "_0" / "_1"
      var idx = -1
      let fname = expr.exprFieldName
      if fname.len > 0 and fname[0] == '_':
        try: idx = parseInt(fname[1..^1])
        except ValueError: idx = -1
      else:
        try: idx = parseInt(fname)
        except ValueError: idx = -1
      if idx >= 0 and idx < objType.inner.len:
        return objType.inner[idx]
      sema.emitError(expr.loc, &"tuple has no element '{fname}' (tuple arity {objType.inner.len})")
      return makeUnknown()
    if objType.kind == tkNamed:
      # Check if this is a _Data union field access
      if objType.name.endsWith("_Data"):
@@ -1468,7 +1482,8 @@ proc checkStmt(sema: var Sema, stmt: Stmt, scope: Scope): Type =
      initType = sema.checkExpr(stmt.stmtLetInit, scope)
    let declaredType = if stmt.stmtLetType != nil: sema.resolveType(stmt.stmtLetType) else: initType
    if stmt.stmtLetInit != nil and stmt.stmtLetType != nil and not initType.isAssignableTo(declaredType) and not (initType.kind in {TypeKind.tkUnknown, TypeKind.tkNamed, TypeKind.tkTypeParam}):
-      sema.emitError(stmt.loc, &"cannot assign {initType.toString} to {declaredType.toString}")
+      # Point at the initializer expression for a clearer caret
      sema.emitError(stmt.stmtLetInit.loc, &"cannot assign {initType.toString} to {declaredType.toString}")
    if stmt.stmtLetInit == nil and stmt.stmtLetType == nil:
      sema.emitError(stmt.loc, "variable must have either type annotation or initializer")
    let isOwnVar = stmt.stmtLetType != nil and stmt.stmtLetType.kind == tekOwn
@@ -3,6 +3,10 @@ type
    line*: uint32      ## 1-based
    column*: uint32    ## 1-based (UTF-8 byte offset in line)
    offset*: uint32    ## byte offset from start of file
    file*: string      ## source file path (empty if unknown)
 proc `$`*(loc: SourceLocation): string =
-  $loc.line & ":" & $loc.column
+  if loc.file.len > 0:
    loc.file & ":" & $loc.line & ":" & $loc.column
  else:
    $loc.line & ":" & $loc.column
@@ -105,10 +105,50 @@ f"Hello, {name}"  // Interpolated string — expressions inside {}
 own T           // Owned value (move semantics)
 T[]             // Slice (unsized)
 T[N]            // Fixed-size array
-(T1, T2, T3)    // Tuple
+(T1, T2, T3)    // Tuple — access fields with .0, .1, .2
-func(T1) -> T2  // Function type
+func(T1) -> T2  // Function pointer type
 ```
 ### Tuples
 ```bux
 func Pair(a: int, b: int) -> (int, int) {
    return (a, b);
 }
 func Main() -> int {
    let t: (int, int) = Pair(10, 20);
    PrintInt(t.0);  // 10
    PrintInt(t.1);  // 20
    return 0;
 }
 ```
 ### Function pointers and closures
 ```bux
 func Apply(f: func(int) -> int, x: int) -> int {
    return f(x);
 }
 func Double(n: int) -> int { return n * 2; }
 func MakeAdder(base: int) -> func(int) -> int {
    // Each call allocates its own capture environment
    return |a: int| -> int { return a + base; };
 }
 func Main() -> int {
    let g: func(int) -> int = Double;   // named func → fat pointer
    let a10 = MakeAdder(10);
    let a20 = MakeAdder(20);
    // a10 and a20 are independent instances
    return Apply(g, 21) + a10(1) + a20(1);  // 42 + 11 + 21
 }
 ```
 `func(T) -> R` values are **fat pointers** `{ code, env }`:
 - capturing closures store captures in a heap env
 - capture-less closures and named functions use `env = null`
 ### Structs
 ```bux
 struct Point {
@@ -0,0 +1,163 @@
 # Bux — План към „добър“ език (v0.5 → v1.0)
 > **Дата:** 2026-07-15  
 > **Текущо:** v0.5.0 — selfhost loop, gradual ownership, green threads, 26+ examples ✅  
 > **Цел:** Език, с който се пишат реални проекти комфортно, безопасно (по избор) и с надежден toolchain.
 ---
 ## Диагноза (къде сме)
 | Слой | Състояние | Оценка |
 |------|-----------|--------|
 | Frontend (lex/parse) | Пълен Pratt parser, recovery | ★★★★☆ |
 | Sema / generics | Monomorphization, trait bounds basic | ★★★★☆ |
 | HIR → C | Работи; tuples/func-ptr half-baked в bootstrap | ★★★☆☆ |
 | Selfhost (`src/`) | ~12k LOC, binary-identical loop | ★★★★★ |
 | Gradual ownership | `@[Checked]`, `&`/`&mut`, move, Drop | ★★★☆☆ (basic) |
 | Concurrency | M:N tasks + channels + async | ★★★★☆ |
 | Stdlib | 25+ модула, но колекциите са минимални | ★★★☆☆ |
 | Tooling | `new/build/run/test/fmt`, LSP prototype, VSCode | ★★☆☆☆ |
 | Ecosystem / registry | path+git deps; няма централен registry | ★☆☆☆☆ |
 | Документация | Има, но drift (PLAN vs README версии) | ★★★☆☆ |
 **Силна ниша:** gradual ownership (C-скорост на писане + opt-in Rust-safety).  
 **Слабо място:** ergonomics на stdlib + maturity на tooling + пълнота на borrow checker.
 ---
 ## Какво значи „добър“ за Bux
 1. **Ежедневен DX** — колекции, string, assert, грешки, които разбираш за секунди.
 2. **Предвидима безопасност** — `@[Checked]` да хваща 80% от UAF/double-borrow без lifetime hell.
 3. **Selfhost като dogfood** — компилаторът и apps (`nexus`, `boko`) са proof.
 4. **Инструменти** — fmt, test, LSP, package install без ръчна магия.
 5. **Стабилна спецификация** — LanguageRef = реалното поведение.
 Не целим „по-добър Rust“. Целим **единствения език с gradual safety + Go-стил concurrency без GC**.
 ---
 ## Фази
 ### A — Ergonomics & Stdlib (P0, сега) 🔄
 | # | Задача | Защо | Статус |
 |---|--------|------|--------|
 | A.1 | Array: Pop, Clear, IsEmpty, First, Last, Cap, Reserve | Без това колекциите са неудобни | ✅ (тази сесия) |
 | A.2 | String: IsEmpty, ReplaceAll | Чести операции; само first-replace досега | ✅ (тази сесия) |
 | A.3 | Os_Exit + Test_AssertEqString / richer asserts | Тестове и CLI без raw `bux_exit` | ✅ (тази сесия) |
 | A.4 | Map_Remove / Set polish | Completeness на колекциите | ✅ (тази сесия) |
 | A.5 | Iter: map/filter/fold върху closures | Higher-order без boilerplate | ⏳ |
 | A.6 | Result helpers: Expect, UnwrapErr, Or | По-малко match boilerplate | ✅ (тази сесия) |
 ### B — Compiler Correctness (P0)
 | # | Задача | Защо | Статус |
 |---|--------|------|--------|
 | B.1 | Proper tuple types в C backend | `(T,U)` → `Tuple_T_U` struct + `.0`/`.1` | ✅ |
 | B.2 | Function pointer types | `func(T)->U` вече работи в LIR backend | ✅ |
 | B.3 | Match expression до край в C (не `return "0"`) | Expression-context match |
 | B.4 | Closures: multi-instance + loop/return в body | Реални higher-order callbacks |
 | B.5 | По-добри diagnostics (snippet + hint) | DX #1 за нови потребители | ✅ |
 | B.6 | Bootstrap ↔ selfhost feature parity | Operator overloading, string interp и в selfhost |
 ### C — Gradual Ownership 2.0 (P1)
 | # | Задача | Защо |
 |---|--------|------|
 | C.1 | Lifetime elision за common cases | Без `'a` в 90% от API-тата |
 | C.2 | Exclusive `&mut` vs shared `&` data-flow | По-малко false negatives |
 | C.3 | Auto-drop edge cases (early return, branches) | RAII да е надежден |
 | C.4 | `@[Release]` zero-cost path документация + golden tests | Killer story: safe default, free hot path |
 ### D — Tooling (P1)
 | # | Задача | Защо |
 |---|--------|------|
 | D.1 | LSP: hover, go-to-def, diagnostics (wire към sema) | IDE = adoption |
 | D.2 | `bux fmt` стабилен + CI check | Единен style |
 | D.3 | `bux test` с `--filter`, exit codes, summary table | CI-friendly |
 | D.4 | `bux doc` от `///` comments | Самодокументиращ се stdlib |
 | D.5 | Golden tests за stdlib modules | Регресии без изненади |
 ### E — Ecosystem & v1.0 (P2)
 | # | Задача | Защо |
 |---|--------|------|
 | E.1 | Package registry protocol (git/HTTP) | `bux add foo` без path hacks |
 | E.2 | 3–5 production-quality apps в `apps/` | Showcase |
 | E.3 | Language freeze + semver policy | Trust |
 | E.4 | Debugger/DWARF basics | Systems audience |
 | E.5 | Benchmarks vs C/Zig/Nim (micro + nexus) | Marketing + regression |
 ---
 ## Препоръчан ред на работа
 ```
 A (stdlib ergonomics)  →  B (compiler holes)  →  C (ownership depth)
        ↓                        ↓
   D (tooling)  ←──────────  dogfood apps
        ↓
   E (v1.0 ecosystem)
 ```
 **Правило:** всяка сесия ship-ва нещо runnable (stdlib API, fix, example), не само docs.
 ---
 ## Acceptance criteria за „добър v1.0“
 - [ ] Всички examples + selfhost-loop + 3 apps минават на CI
 - [ ] Array/Map/String/Test API покрива 90% от ежедневните нужди
 - [ ] `@[Checked]` хваща use-after-move + double `&mut` в documented subset
 - [ ] `bux test` + `bux fmt` + `bux check` са default developer loop
 - [ ] LanguageRef синхронизиран с компилатора
 - [ ] Поне един външен проект (не в monorepo) build-ва с git dep
 ---
 ## Сесия 1 (stdlib ergonomics)
 1. `Array_Pop`, `Array_Clear`, `Array_IsEmpty`, `Array_First`, `Array_Last`, `Array_Cap`, `Array_Reserve`
 2. `String_IsEmpty`, `String_ReplaceAll`
 3. `Os_Exit`
 4. `Test_AssertEqString`, `Test_AssertNeqInt`, `Test_AssertEqBool`
 5. Example + docs update
 ## Сесия 2 (collections + tuples)
 1. `Map_Remove` / `Map_Clear` / `Map_IsEmpty` (+ StringMap)
 2. `Set_Remove` / `Set_Clear` / `Set_IsEmpty`
 3. `Result_Expect` / `Result_UnwrapErr` / `Result_Or`
 4. `Option_Expect` / `Option_Or`
 5. **Tuples:** `(T, U)` → `typedef struct { T _0; U _1; } Tuple_T_U` + field access `.0`/`.1`
 6. Examples: `tuples`, `func_ptr`, `map_remove`
 ## Сесия 3 (diagnostics + collections)
 1. **Rust-style errors** in bootstrap CLI: `--> file:line:col`, source snippet, `^` caret, `= help:` hints
 2. `SourceLocation.file` propagated from lexer
 3. Better caret for type-mismatch on `let` (points at initializer)
 4. `Array_Contains` / `Array_IndexOf` / `Array_Extend`
 5. `Iter_AnyEq` / `Iter_AllEq` / `Iter_Collect`
 6. Selfhost `Diagnostic_Hint` for common messages
 ## Сесия 4 (diagnostics depth + LSP + strings)
 1. **Multi-char underlines** (`^^^^^^^` under tokens/strings/idents)
 2. Quoted-name highlighting for `undeclared identifier 'x'`
 3. **Golden error tests** (`tests/error_golden/`, `make test-errors`)
 4. **LSP** runs `buxc check` and publishes real diagnostics
 5. `String_IsBlank` / `String_Repeat`
 ## Сесия 5 (multi-instance closures)
 1. **Fat function pointers** for all `func(...)` types: `BuxFn { code(env, args...), env }`
 2. Capturing closures: heap-allocate env per creation site (independent instances)
 3. Capture-less closures + named funcs: adapters with `env = NULL`
 4. Calls through func values: `f.code(f.env, args...)`
 5. Example `multi_closure.bux` — MakeAdder(10)/MakeAdder(20) yield 11 and 21
 6. **Selfhost parity:** same fat ABI in `src/hir_lower.bux` + `src/c_backend.bux` (makers, adapters)
 ```
@@ -153,7 +153,9 @@ Array_Filter(nums, |x| { return x > 10; });
  4. In thunk body: rewrite captured identifiers to `env_instance.x` via `hFieldAccess`.
  5. C backend: emit env struct definition + global instance before thunk function.
-**Limitations:** One global instance per closure AST node (no multiple instances). No loop/return support in closures yet.
+**Status:** Multi-instance capturing closures work in **both** bootstrap and selfhost via fat
 function pointers (`BuxFn { code, env }` + heap-allocated env per creation). Capture-less
 closures and named functions use the same ABI (`env = NULL`, adapters for named funcs).
 **Complexity:** High — touches parser, sema, type system, HIR/LIR backend.
@@ -81,8 +81,19 @@ struct Array<T> {
 |----------|-----------|-------------|
 | `Array_New<T>` | `func Array_New<T>(cap: uint) -> Array<T>` | Create new array |
 | `Array_Push<T>` | `func Array_Push<T>(arr: *Array<T>, value: T)` | Append element |
 | `Array_Pop<T>` | `func Array_Pop<T>(arr: *Array<T>) -> T` | Remove and return last element |
 | `Array_Contains<T>` | `func Array_Contains<T>(arr: *Array<T>, value: T) -> bool` | Linear search for value |
 | `Array_IndexOf<T>` | `func Array_IndexOf<T>(arr: *Array<T>, value: T) -> int` | First index or -1 |
 | `Array_Extend<T>` | `func Array_Extend<T>(arr: *Array<T>, other: *Array<T>)` | Append all from other |
 | `Array_Get<T>` | `func Array_Get<T>(arr: *Array<T>, index: uint) -> T` | Get element at index |
 | `Array_Set<T>` | `func Array_Set<T>(arr: *Array<T>, index: uint, value: T)` | Set element at index |
 | `Array_First<T>` | `func Array_First<T>(arr: *Array<T>) -> T` | First element (bounds-checked) |
 | `Array_Last<T>` | `func Array_Last<T>(arr: *Array<T>) -> T` | Last element (bounds-checked) |
 | `Array_Len<T>` | `func Array_Len<T>(arr: *Array<T>) -> uint` | Get length |
 | `Array_Cap<T>` | `func Array_Cap<T>(arr: *Array<T>) -> uint` | Get capacity |
 | `Array_IsEmpty<T>` | `func Array_IsEmpty<T>(arr: *Array<T>) -> bool` | True if length is 0 |
 | `Array_Clear<T>` | `func Array_Clear<T>(arr: *Array<T>)` | Set length to 0 (keeps capacity) |
 | `Array_Reserve<T>` | `func Array_Reserve<T>(arr: *Array<T>, minCap: uint)` | Grow capacity if needed |
 | `Array_Free<T>` | `func Array_Free<T>(arr: *Array<T>)` | Free memory |
 ### Example
@@ -128,6 +139,9 @@ struct Iter<T> {
 | `Iter_Count<T>` | `func Iter_Count<T>(it: *Iter<T>) -> uint` | Count remaining elements |
 | `Iter_Skip<T>` | `func Iter_Skip<T>(it: *Iter<T>, n: uint)` | Skip N elements |
 | `Iter_Take<T>` | `func Iter_Take<T>(it: *Iter<T>, n: uint) -> Iter<T>` | Take first N elements as new iterator |
 | `Iter_AnyEq<T>` | `func Iter_AnyEq<T>(it: *Iter<T>, value: T) -> bool` | True if any remaining element equals value |
 | `Iter_AllEq<T>` | `func Iter_AllEq<T>(it: *Iter<T>, value: T) -> bool` | True if all remaining equal value |
 | `Iter_Collect<T>` | `func Iter_Collect<T>(it: *Iter<T>) -> Array<T>` | Collect remaining into a new Array |
 ### Example
 ```bux
@@ -200,8 +214,12 @@ String manipulation utilities.
 | Function | Signature | Description |
 |----------|-----------|-------------|
 | `String_IsEmpty` | `func String_IsEmpty(s: String) -> bool` | True if length is 0 |
 | `String_IsBlank` | `func String_IsBlank(s: String) -> bool` | True if empty or only whitespace |
 | `String_Repeat` | `func String_Repeat(s: String, count: uint) -> String` | Repeat string N times |
 | `String_Find` | `func String_Find(haystack: String, needle: String) -> String` | Find substring (returns pointer; 0 = not found) |
 | `String_Replace` | `func String_Replace(s: String, old: String, new: String) -> String` | Replace first occurrence |
 | `String_ReplaceAll` | `func String_ReplaceAll(s: String, old: String, new: String) -> String` | Replace all non-overlapping occurrences |
 | `String_Format1` | `func String_Format1(pattern: String, a0: String) -> String` | Format with 1 arg (`{0}`) |
 | `String_Format2` | `func String_Format2(pattern: String, a0: String, a1: String) -> String` | Format with 2 args |
 | `String_Format3` | `func String_Format3(pattern: String, a0: String, a1: String, a2: String) -> String` | Format with 3 args |
@@ -322,6 +340,9 @@ struct Set<T> {
 | `Set_New<T>` | `func Set_New<T>(cap: uint) -> Set<T>` | Create set |
 | `Set_Add<T>` | `func Set_Add<T>(s: *Set<T>, value: T)` | Insert element (ignores duplicates) |
 | `Set_Has<T>` | `func Set_Has<T>(s: *Set<T>, value: T) -> bool` | Check membership |
 | `Set_Remove<T>` | `func Set_Remove<T>(s: *Set<T>, value: T) -> bool` | Remove value |
 | `Set_Clear<T>` | `func Set_Clear<T>(s: *Set<T>)` | Clear all elements |
 | `Set_IsEmpty<T>` | `func Set_IsEmpty<T>(s: *Set<T>) -> bool` | True if empty |
 | `Set_Len<T>` | `func Set_Len<T>(s: *Set<T>) -> uint` | Element count |
 | `Set_Free<T>` | `func Set_Free<T>(s: *Set<T>)` | Free memory |
@@ -371,6 +392,9 @@ struct Map<K, V> {
 | `Map_Set<K,V>` | `func Map_Set<K,V>(m: *Map<K,V>, key: K, value: V)` | Insert/update |
 | `Map_Get<K,V>` | `func Map_Get<K,V>(m: *Map<K,V>, key: K) -> V` | Get value (zero if missing) |
 | `Map_Has<K,V>` | `func Map_Has<K,V>(m: *Map<K,V>, key: K) -> bool` | Check key exists |
 | `Map_Remove<K,V>` | `func Map_Remove<K,V>(m: *Map<K,V>, key: K) -> bool` | Remove key (true if present) |
 | `Map_Clear<K,V>` | `func Map_Clear<K,V>(m: *Map<K,V>)` | Remove all entries (keeps capacity) |
 | `Map_IsEmpty<K,V>` | `func Map_IsEmpty<K,V>(m: *Map<K,V>) -> bool` | True if no entries |
 | `Map_Len<K,V>` | `func Map_Len<K,V>(m: *Map<K,V>) -> uint` | Entry count |
 | `Map_Free<K,V>` | `func Map_Free<K,V>(m: *Map<K,V>)` | Free memory |
@@ -419,6 +443,9 @@ struct StringMap<V> {
 | `StringMap_Set<V>` | `func StringMap_Set<V>(m: *StringMap<V>, key: String, value: V)` | Insert/update |
 | `StringMap_Get<V>` | `func StringMap_Get<V>(m: *StringMap<V>, key: String) -> V` | Get value |
 | `StringMap_Has<V>` | `func StringMap_Has<V>(m: *StringMap<V>, key: String) -> bool` | Check key exists |
 | `StringMap_Remove<V>` | `func StringMap_Remove<V>(m: *StringMap<V>, key: String) -> bool` | Remove key |
 | `StringMap_Clear<V>` | `func StringMap_Clear<V>(m: *StringMap<V>)` | Clear all entries |
 | `StringMap_IsEmpty<V>` | `func StringMap_IsEmpty<V>(m: *StringMap<V>) -> bool` | True if empty |
 | `StringMap_Len<V>` | `func StringMap_Len<V>(m: *StringMap<V>) -> uint` | Entry count |
 | `StringMap_Free<V>` | `func StringMap_Free<V>(m: *StringMap<V>)` | Free memory |
@@ -914,7 +941,7 @@ func Main() -> int {
 Operating system interface.
 ```bux
-import Std::Os::{Os_ArgsCount, Os_Args, Os_GetEnv, Os_SetEnv, Os_GetCwd, Os_Chdir};
+import Std::Os::{Os_ArgsCount, Os_Args, Os_GetEnv, Os_SetEnv, Os_GetCwd, Os_Chdir, Os_Exit};
 ```
 | Function | Signature | Description |
@@ -925,6 +952,28 @@ import Std::Os::{Os_ArgsCount, Os_Args, Os_GetEnv, Os_SetEnv, Os_GetCwd, Os_Chdi
 | `Os_SetEnv` | `func Os_SetEnv(name: String, value: String) -> bool` | Set environment variable |
 | `Os_GetCwd` | `func Os_GetCwd() -> String` | Get current working directory |
 | `Os_Chdir` | `func Os_Chdir(path: String) -> bool` | Change directory |
 | `Os_Exit` | `func Os_Exit(code: int)` | Terminate process with exit code |
 ---
 ## Std::Test
 Lightweight assertions for `bux test` and example programs.
 ```bux
 import Std::Test::*;
 ```
 | Function | Signature | Description |
 |----------|-----------|-------------|
 | `Test_Assert` | `func Test_Assert(cond: bool)` | Panic if false |
 | `Test_AssertTrue` / `Test_AssertFalse` | `func ...(cond: bool)` | Boolean asserts |
 | `Test_AssertEqInt` | `func Test_AssertEqInt(a: int, b: int)` | Integer equality |
 | `Test_AssertNeqInt` | `func Test_AssertNeqInt(a: int, b: int)` | Integer inequality |
 | `Test_AssertEqString` | `func Test_AssertEqString(a: String, b: String)` | String equality |
 | `Test_AssertEqBool` | `func Test_AssertEqBool(a: bool, b: bool)` | Boolean equality |
 | `Test_Fail` / `Test_Pass` | `func ...(msg: String)` | Explicit fail / log pass |
 | `Test_Exit` | `func Test_Exit(code: int)` | Exit with code |
 ---
@@ -0,0 +1,46 @@
 // Array_Contains / IndexOf / Extend + Iter_Collect / AnyEq
 import Std::Io::{PrintLine, PrintInt};
 import Std::Array::{
    Array, Array_New, Array_Push, Array_Contains, Array_IndexOf,
    Array_Extend, Array_Len, Array_Get, Array_Free
 };
 import Std::Iter::{Array_Iter, Iter, Iter_Collect, Iter_AnyEq, Iter_AllEq, Iter_HasNext, Iter_Next};
 import Std::Test::{Test_AssertTrue, Test_AssertFalse, Test_AssertEqInt, Test_Pass};
 func Main() -> int {
    var a: Array<int> = Array_New<int>(4);
    Array_Push<int>(&a, 10);
    Array_Push<int>(&a, 20);
    Array_Push<int>(&a, 30);
    Test_AssertTrue(Array_Contains<int>(&a, 20));
    Test_AssertFalse(Array_Contains<int>(&a, 99));
    Test_AssertEqInt(Array_IndexOf<int>(&a, 30), 2);
    Test_AssertEqInt(Array_IndexOf<int>(&a, 99), -1);
    var b: Array<int> = Array_New<int>(2);
    Array_Push<int>(&b, 40);
    Array_Push<int>(&b, 50);
    Array_Extend<int>(&a, &b);
    Test_AssertEqInt(Array_Len<int>(&a) as int, 5);
    Test_AssertEqInt(Array_Get<int>(&a, 4), 50);
    var it: Iter<int> = Array_Iter<int>(&a);
    Test_AssertTrue(Iter_AnyEq<int>(&it, 10));
    Test_AssertFalse(Iter_AllEq<int>(&it, 10));
    // Skip first two via advancing, collect rest
    discard Iter_Next<int>(&it);
    discard Iter_Next<int>(&it);
    var rest: Array<int> = Iter_Collect<int>(&it);
    Test_AssertEqInt(Array_Len<int>(&rest) as int, 3);
    Test_AssertEqInt(Array_Get<int>(&rest, 0), 30);
    Array_Free<int>(&a);
    Array_Free<int>(&b);
    Array_Free<int>(&rest);
    PrintLine("array_iter_extra: ok");
    Test_Pass("array + iter extras");
    return 0;
 }
@@ -0,0 +1,27 @@
 // Function pointer types: func(T) -> U
 import Std::Io::{PrintLine, PrintInt};
 import Std::Test::{Test_AssertEqInt, Test_Pass};
 func Apply(f: func(int) -> int, x: int) -> int {
    return f(x);
 }
 func Double(n: int) -> int {
    return n * 2;
 }
 func Inc(n: int) -> int {
    return n + 1;
 }
 func Main() -> int {
    let g: func(int) -> int = Double;
    Test_AssertEqInt(Apply(g, 21), 42);
    Test_AssertEqInt(Apply(Double, 7), 14);
    Test_AssertEqInt(Apply(Inc, 99), 100);
    PrintInt(Apply(Double, 5));
    PrintLine("");
    Test_Pass("func_ptr");
    return 0;
 }
@@ -0,0 +1,60 @@
 // Map_Remove / Map_Clear / Set_Remove
 import Std::Io::{PrintLine, PrintInt};
 import Std::Map::{Map, Map_New, Map_Set, Map_Get, Map_Has, Map_Remove, Map_Clear, Map_Len, Map_IsEmpty, Map_Free};
 import Std::Set::{Set, Set_New, Set_Add, Set_Has, Set_Remove, Set_Len, Set_IsEmpty, Set_Free};
 import Std::Test::{Test_AssertTrue, Test_AssertFalse, Test_AssertEqInt, Test_Pass};
 import Std::Result::{Result, Result_NewOk, Result_NewErr, Result_IsOk, Result_IsErr, Result_UnwrapOr, Result_Or, Result_UnwrapErr};
 import Std::Option::{Option, Option_NewSome, Option_NewNone, Option_IsSome, Option_Or, Option_UnwrapOr};
 import Std::String::{String_Eq};
 func Main() -> int {
    // --- Map ---
    var m: Map<int, int> = Map_New<int, int>(16);
    Map_Set<int, int>(&m, 1, 100);
    Map_Set<int, int>(&m, 2, 200);
    Map_Set<int, int>(&m, 3, 300);
    Test_AssertEqInt(Map_Len<int, int>(&m) as int, 3);
    Test_AssertTrue(Map_Has<int, int>(&m, 2));
    Test_AssertTrue(Map_Remove<int, int>(&m, 2));
    Test_AssertFalse(Map_Has<int, int>(&m, 2));
    Test_AssertEqInt(Map_Len<int, int>(&m) as int, 2);
    Test_AssertEqInt(Map_Get<int, int>(&m, 1), 100);
    Test_AssertEqInt(Map_Get<int, int>(&m, 3), 300);
    Test_AssertFalse(Map_Remove<int, int>(&m, 99));
    Map_Clear<int, int>(&m);
    Test_AssertTrue(Map_IsEmpty<int, int>(&m));
    Map_Free<int, int>(&m);
    // --- Set ---
    var s: Set<int> = Set_New<int>(16);
    Set_Add<int>(&s, 10);
    Set_Add<int>(&s, 20);
    Set_Add<int>(&s, 30);
    Test_AssertTrue(Set_Remove<int>(&s, 20));
    Test_AssertFalse(Set_Has<int>(&s, 20));
    Test_AssertTrue(Set_Has<int>(&s, 10));
    Test_AssertEqInt(Set_Len<int>(&s) as int, 2);
    Test_AssertFalse(Set_IsEmpty<int>(&s));
    Set_Free<int>(&s);
    // --- Result helpers ---
    let ok: Result = Result_NewOk(42);
    let err: Result = Result_NewErr("boom");
    Test_AssertTrue(Result_IsOk(ok));
    Test_AssertTrue(Result_IsErr(err));
    Test_AssertEqInt(Result_UnwrapOr(err, -1), -1);
    let recovered: Result = Result_Or(err, Result_NewOk(7));
    Test_AssertEqInt(Result_UnwrapOr(recovered, 0), 7);
    Test_AssertTrue(String_Eq(Result_UnwrapErr(err), "boom"));
    // --- Option helpers ---
    let some: Option = Option_NewSome(5);
    let none: Option = Option_NewNone();
    Test_AssertTrue(Option_IsSome(some));
    let o2: Option = Option_Or(none, some);
    Test_AssertEqInt(Option_UnwrapOr(o2, 0), 5);
    PrintLine("map_remove: ok");
    Test_Pass("map_remove + result helpers");
    return 0;
 }
@@ -0,0 +1,37 @@
 // Multi-instance closures: each capturing closure gets its own heap env
 import Std::Io::{PrintLine, PrintInt};
 import Std::Test::{Test_AssertEqInt, Test_Pass};
 func MakeAdder(base: int) -> func(int) -> int {
    return |a: int| -> int {
        return a + base;
    };
 }
 func Apply(f: func(int) -> int, x: int) -> int {
    return f(x);
 }
 func Main() -> int {
    let a10: func(int) -> int = MakeAdder(10);
    let a20: func(int) -> int = MakeAdder(20);
    // Independent instances — not a single global env
    Test_AssertEqInt(a10(1), 11);
    Test_AssertEqInt(a20(1), 21);
    Test_AssertEqInt(a10(5), 15);
    Test_AssertEqInt(Apply(a20, 3), 23);
    // Capture-less still works
    let add: func(int, int) -> int = |x: int, y: int| -> int {
        return x + y;
    };
    Test_AssertEqInt(add(2, 3), 5);
    PrintInt(a10(1));
    PrintLine("");
    PrintInt(a20(1));
    PrintLine("");
    Test_Pass("multi_closure");
    return 0;
 }
@@ -0,0 +1,55 @@
 // Stdlib ergonomics demo: Array helpers, String_ReplaceAll, Test asserts
 import Std::Io::{PrintLine, PrintInt};
 import Std::Array::{
    Array, Array_New, Array_Push, Array_Pop, Array_Clear, Array_IsEmpty,
    Array_First, Array_Last, Array_Cap, Array_Reserve, Array_Len, Array_Get, Array_Free
 };
 import Std::String::{String_IsEmpty, String_ReplaceAll, String_Eq, String_Len};
 import Std::Test::{
    Test_AssertTrue, Test_AssertFalse, Test_AssertEqInt, Test_AssertEqString,
    Test_AssertNeqInt, Test_AssertEqBool, Test_Pass
 };
 func Main() -> int {
    // --- Array: Reserve / Push / First / Last / Pop / Clear ---
    var arr: Array<int> = Array_New<int>(2);
    Array_Reserve<int>(&arr, 8);
    Test_AssertTrue(Array_Cap<int>(&arr) >= 8);
    Test_AssertTrue(Array_IsEmpty<int>(&arr));
    Array_Push<int>(&arr, 10);
    Array_Push<int>(&arr, 20);
    Array_Push<int>(&arr, 30);
    Test_AssertFalse(Array_IsEmpty<int>(&arr));
    Test_AssertEqInt(Array_Len<int>(&arr) as int, 3);
    Test_AssertEqInt(Array_First<int>(&arr), 10);
    Test_AssertEqInt(Array_Last<int>(&arr), 30);
    let popped: int = Array_Pop<int>(&arr);
    Test_AssertEqInt(popped, 30);
    Test_AssertEqInt(Array_Len<int>(&arr) as int, 2);
    Test_AssertEqInt(Array_Get<int>(&arr, 1), 20);
    Array_Clear<int>(&arr);
    Test_AssertTrue(Array_IsEmpty<int>(&arr));
    Test_AssertTrue(Array_Cap<int>(&arr) >= 8);  // capacity retained
    Array_Free<int>(&arr);
    // --- String: IsEmpty / ReplaceAll ---
    Test_AssertTrue(String_IsEmpty(""));
    Test_AssertFalse(String_IsEmpty("x"));
    let multi: String = String_ReplaceAll("a-b-a-b-a", "a", "X");
    Test_AssertEqString(multi, "X-b-X-b-X");
    Test_AssertNeqInt(String_Len(multi) as int, 0);
    // Safe when replacement contains the needle (no infinite loop)
    let safe: String = String_ReplaceAll("..", ".", "x.");
    Test_AssertEqString(safe, "x.x.");
    Test_AssertEqBool(true, true);
    Test_Pass("stdlib ergonomics");
    PrintLine("stdlib_ergonomics: all checks passed");
    return 0;
 }
@@ -0,0 +1,21 @@
 // String_IsBlank / String_Repeat
 import Std::Io::{PrintLine};
 import Std::String::{String_IsBlank, String_IsEmpty, String_Repeat, String_Eq, String_Len};
 import Std::Test::{Test_AssertTrue, Test_AssertFalse, Test_AssertEqInt, Test_AssertEqString, Test_Pass};
 func Main() -> int {
    Test_AssertTrue(String_IsEmpty(""));
    Test_AssertTrue(String_IsBlank(""));
    Test_AssertTrue(String_IsBlank("   \t\n"));
    Test_AssertFalse(String_IsBlank(" x "));
    let dots: String = String_Repeat(".", 5);
    Test_AssertEqString(dots, ".....");
    Test_AssertEqInt(String_Len(String_Repeat("ab", 3)) as int, 6);
    Test_AssertEqString(String_Repeat("x", 0), "");
    Test_AssertEqString(String_Repeat("ok", 1), "ok");
    PrintLine(String_Repeat("Bux ", 2));
    Test_Pass("string_extra");
    return 0;
 }
@@ -0,0 +1,32 @@
 // Tuple types: (T, U), return, field access via .0 / .1
 import Std::Io::{PrintLine, PrintInt};
 import Std::Test::{Test_AssertEqInt, Test_Pass};
 func MakePair(a: int, b: int) -> (int, int) {
    return (a, b);
 }
 func Swap(t: (int, int)) -> (int, int) {
    return (t.1, t.0);
 }
 func Main() -> int {
    let t: (int, int) = MakePair(10, 20);
    Test_AssertEqInt(t.0, 10);
    Test_AssertEqInt(t.1, 20);
    let s: (int, int) = Swap(t);
    Test_AssertEqInt(s.0, 20);
    Test_AssertEqInt(s.1, 10);
    let lit: (int, int) = (7, 8);
    Test_AssertEqInt(lit.0, 7);
    Test_AssertEqInt(lit.1, 8);
    PrintInt(t.0);
    PrintLine("");
    PrintInt(t.1);
    PrintLine("");
    Test_Pass("tuples");
    return 0;
 }
@@ -58,4 +58,78 @@ func Array_operator_index_set<T>(self: *Array<T>, idx: uint, value: T) {
    Array_Set<T>(self, idx, value);
 }
 /* True if the array has no elements */
 func Array_IsEmpty<T>(self: *Array<T>) -> bool {
    return self.len == 0;
 }
 /* Current capacity (not length) */
 func Array_Cap<T>(self: *Array<T>) -> uint {
    return self.cap;
 }
 /* Drop length to zero; keeps allocated capacity */
 func Array_Clear<T>(self: *Array<T>) {
    self.len = 0;
 }
 /* Ensure capacity is at least minCap (does not shrink) */
 func Array_Reserve<T>(self: *Array<T>, minCap: uint) {
    if minCap <= self.cap {
        return;
    }
    self.cap = minCap;
    self.data = bux_realloc(self.data as *void, self.cap * sizeof(T)) as *T;
 }
 /* First element (panics if empty via bounds check) */
 func Array_First<T>(self: *Array<T>) -> T {
    return Array_Get<T>(self, 0);
 }
 /* Last element (panics if empty via bounds check) */
 func Array_Last<T>(self: *Array<T>) -> T {
    return Array_Get<T>(self, self.len - 1);
 }
 /* Remove and return the last element (panics if empty) */
 func Array_Pop<T>(self: *Array<T>) -> T {
    bux_bounds_check(0, self.len);
    self.len = self.len - 1;
    return self.data[self.len];
 }
 /* Linear search: true if value is present (uses ==) */
 func Array_Contains<T>(self: *Array<T>, value: T) -> bool {
    var i: uint = 0;
    while i < self.len {
        if self.data[i] == value {
            return true;
        }
        i = i + 1;
    }
    return false;
 }
 /* Index of first equal element, or -1 if not found */
 func Array_IndexOf<T>(self: *Array<T>, value: T) -> int {
    var i: uint = 0;
    while i < self.len {
        if self.data[i] == value {
            return i as int;
        }
        i = i + 1;
    }
    return -1;
 }
 /* Append all elements of other onto self */
 func Array_Extend<T>(self: *Array<T>, other: *Array<T>) {
    var i: uint = 0;
    while i < other.len {
        Array_Push<T>(self, other.data[i]);
        i = i + 1;
    }
 }
 }
@@ -67,4 +67,44 @@ func Iter_Take<T>(it: *Iter<T>, n: uint) -> Iter<T> {
    return Iter<T> { data: it.data, len: endPos, pos: it.pos };
 }
 /* True if any remaining element equals value */
 func Iter_AnyEq<T>(it: *Iter<T>, value: T) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if it.data[i] == value {
            return true;
        }
        i = i + 1;
    }
    return false;
 }
 /* True if every remaining element equals value (true if empty) */
 func Iter_AllEq<T>(it: *Iter<T>, value: T) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if it.data[i] != value {
            return false;
        }
        i = i + 1;
    }
    return true;
 }
 /* Collect remaining elements into a new Array */
 func Iter_Collect<T>(it: *Iter<T>) -> Array<T> {
    let remaining: uint = it.len - it.pos;
    var cap: uint = remaining;
    if cap == 0 {
        cap = 1;
    }
    var arr: Array<T> = Array_New<T>(cap);
    var i: uint = it.pos;
    while i < it.len {
        Array_Push<T>(&arr, it.data[i]);
        i = i + 1;
    }
    return arr;
 }
 }
@@ -80,6 +80,41 @@ func Map_Len<K, V>(m: *Map<K, V>) -> uint {
    return m.len;
 }
 func Map_IsEmpty<K, V>(m: *Map<K, V>) -> bool {
    return m.len == 0;
 }
 /* Remove key if present. Rebuilds the table to keep open-addressing correct. */
 func Map_Remove<K, V>(m: *Map<K, V>, key: K) -> bool {
    if !Map_Has<K, V>(m, key) {
        return false;
    }
    var fresh: Map<K, V> = Map_New<K, V>(m.cap);
    var i: uint = 0;
    while i < m.cap {
        if m.entries[i].occupied {
            if m.entries[i].key != key {
                Map_Set<K, V>(&fresh, m.entries[i].key, m.entries[i].value);
            }
        }
        i = i + 1;
    }
    bux_free(m.entries as *void);
    m.entries = fresh.entries;
    m.cap = fresh.cap;
    m.len = fresh.len;
    return true;
 }
 func Map_Clear<K, V>(m: *Map<K, V>) {
    var i: uint = 0;
    while i < m.cap {
        m.entries[i].occupied = false;
        i = i + 1;
    }
    m.len = 0;
 }
 func Map_Free<K, V>(m: *Map<K, V>) {
    bux_free(m.entries as *void);
    m.entries = null as *MapEntry<K, V>;
@@ -163,6 +198,40 @@ func StringMap_Len<V>(m: *StringMap<V>) -> uint {
    return m.len;
 }
 func StringMap_IsEmpty<V>(m: *StringMap<V>) -> bool {
    return m.len == 0;
 }
 func StringMap_Remove<V>(m: *StringMap<V>, key: String) -> bool {
    if !StringMap_Has<V>(m, key) {
        return false;
    }
    var fresh: StringMap<V> = StringMap_New<V>(m.cap);
    var i: uint = 0;
    while i < m.cap {
        if m.entries[i].occupied {
            if !String_Eq(m.entries[i].key, key) {
                StringMap_Set<V>(&fresh, m.entries[i].key, m.entries[i].value);
            }
        }
        i = i + 1;
    }
    bux_free(m.entries as *void);
    m.entries = fresh.entries;
    m.cap = fresh.cap;
    m.len = fresh.len;
    return true;
 }
 func StringMap_Clear<V>(m: *StringMap<V>) {
    var i: uint = 0;
    while i < m.cap {
        m.entries[i].occupied = false;
        i = i + 1;
    }
    m.len = 0;
 }
 func StringMap_Free<V>(m: *StringMap<V>) {
    bux_free(m.entries as *void);
    m.entries = null as *StringMapEntry<V>;
@@ -1,6 +1,8 @@
 module Std::Option {
 import Std::Io::{PrintLine};
 extern func bux_exit(code: int);
 enum Option {
    Some(int),
    None,
@@ -39,4 +41,21 @@ func Option_UnwrapOr(o: Option, fallback: int) -> int {
    return fallback;
 }
 /* Unwrap Some or panic with a custom message */
 func Option_Expect(o: Option, msg: String) -> int {
    if o.tag != Option_Some {
        PrintLine(msg);
        bux_exit(1);
    }
    return o.data.Some_0;
 }
 /* If o is Some return it, otherwise return other */
 func Option_Or(o: Option, other: Option) -> Option {
    if o.tag == Option_Some {
        return o;
    }
    return other;
 }
 }
@@ -6,6 +6,7 @@ extern func bux_getenv(name: String) -> String;
 extern func bux_setenv(name: String, value: String) -> int;
 extern func bux_getcwd() -> String;
 extern func bux_chdir(path: String) -> int;
 extern func bux_exit(code: int);
 func Os_ArgsCount() -> int {
    return bux_argc();
@@ -31,4 +32,9 @@ func Os_Chdir(path: String) -> bool {
    return bux_chdir(path) == 0;
 }
 /* Terminate the process with the given exit code */
 func Os_Exit(code: int) {
    bux_exit(code);
 }
 }
@@ -1,6 +1,8 @@
 module Std::Result {
 import Std::Io::{PrintLine};
 extern func bux_exit(code: int);
 enum Result {
    Ok(int),
    Err(String),
@@ -41,4 +43,30 @@ func Result_UnwrapOr(r: Result, fallback: int) -> int {
    return fallback;
 }
 /* Unwrap Ok or panic with a custom message */
 func Result_Expect(r: Result, msg: String) -> int {
    if r.tag != Result_Ok {
        PrintLine(msg);
        bux_exit(1);
    }
    return r.data.Ok_0;
 }
 /* Extract Err payload (panics if Ok) */
 func Result_UnwrapErr(r: Result) -> String {
    if r.tag != Result_Err {
        PrintLine("panic: unwrap_err on Ok");
        return "";
    }
    return r.data.Err_0;
 }
 /* If r is Ok return it, otherwise return other */
 func Result_Or(r: Result, other: Result) -> Result {
    if r.tag == Result_Ok {
        return r;
    }
    return other;
 }
 }
@@ -61,6 +61,43 @@ func Set_Len<T>(s: *Set<T>) -> uint {
    return s.len;
 }
 func Set_IsEmpty<T>(s: *Set<T>) -> bool {
    return s.len == 0;
 }
 /* Remove value if present. Rebuilds the table to keep open-addressing correct. */
 func Set_Remove<T>(s: *Set<T>, value: T) -> bool {
    if !Set_Has<T>(s, value) {
        return false;
    }
    var fresh: Set<T> = Set_New<T>(s.cap);
    var i: uint = 0;
    while i < s.cap {
        if s.entries[i].occupied {
            var entryPtr: *T = &s.entries[i].value;
            var valuePtr: *T = &value;
            if bux_mem_eq(entryPtr as *void, valuePtr as *void, sizeof(T)) == 0 {
                Set_Add<T>(&fresh, s.entries[i].value);
            }
        }
        i = i + 1;
    }
    bux_free(s.entries as *void);
    s.entries = fresh.entries;
    s.cap = fresh.cap;
    s.len = fresh.len;
    return true;
 }
 func Set_Clear<T>(s: *Set<T>) {
    var i: uint = 0;
    while i < s.cap {
        s.entries[i].occupied = false;
        i = i + 1;
    }
    s.len = 0;
 }
 func Set_Free<T>(s: *Set<T>) {
    bux_free(s.entries as *void);
    s.entries = null as *SetEntry<T>;
@@ -34,6 +34,10 @@ func String_Len(s: String) -> uint {
    return bux_strlen(s);
 }
 func String_IsEmpty(s: String) -> bool {
    return bux_strlen(s) == 0;
 }
 func String_IsNull(s: String) -> bool {
    return bux_str_is_null(s) != 0;
 }
@@ -147,6 +151,39 @@ func StringBuilder_Free(sb: *StringBuilder) {
    bux_sb_free(sb.handle);
 }
 /* True if empty or only whitespace (space, tab, CR, LF) */
 func String_IsBlank(s: String) -> bool {
    let n: uint = bux_strlen(s);
    var i: uint = 0;
    while i < n {
        let ch: String = bux_str_slice(s, i, 1);
        if !(String_Eq(ch, " ") || String_Eq(ch, "\t") || String_Eq(ch, "\n") || String_Eq(ch, "\r")) {
            return false;
        }
        i = i + 1;
    }
    return true;
 }
 /* Repeat s, count times (count==0 → empty string) */
 func String_Repeat(s: String, count: uint) -> String {
    if count == 0 {
        return "";
    }
    if count == 1 {
        return s;
    }
    var sb: StringBuilder = StringBuilder_New();
    var i: uint = 0;
    while i < count {
        StringBuilder_Append(&sb, s);
        i = i + 1;
    }
    let result: String = StringBuilder_Build(&sb);
    StringBuilder_Free(&sb);
    return result;
 }
 // ---------------------------------------------------------------------------
 // String split/join
 // ---------------------------------------------------------------------------
@@ -194,6 +231,33 @@ func String_Replace(s: String, old: String, new: String) -> String {
    return result;
 }
 /* Replace every non-overlapping occurrence of old with new.
   Empty old is a no-op (returns s unchanged). Safe if new contains old. */
 func String_ReplaceAll(s: String, old: String, new: String) -> String {
    let oldLen: uint = bux_strlen(old);
    if oldLen == 0 {
        return s;
    }
    var sb: StringBuilder = StringBuilder_New();
    var remaining: String = s;
    while true {
        let pos: String = bux_strstr(remaining, old);
        if String_IsNull(pos) {
            StringBuilder_Append(&sb, remaining);
            break;
        }
        let prefixLen: uint = String_Offset(pos, remaining);
        let prefix: String = bux_str_slice(remaining, 0, prefixLen);
        StringBuilder_Append(&sb, prefix);
        StringBuilder_Append(&sb, new);
        let remLen: uint = bux_strlen(remaining);
        remaining = bux_str_slice(remaining, prefixLen + oldLen, remLen - prefixLen - oldLen);
    }
    let result: String = StringBuilder_Build(&sb);
    StringBuilder_Free(&sb);
    return result;
 }
 extern func bux_str_to_float(s: String) -> float64;
 func String_ToFloat(s: String) -> float64 {
@@ -1,5 +1,6 @@
 module Std::Test {
 import Std::Io::{PrintLine, PrintInt};
 import Std::String::{String_Eq};
 extern func bux_exit(code: int);
 extern func bux_assert(cond: int, file: String, line: int, expr: String);
@@ -14,7 +15,7 @@ func Test_Assert(cond: bool) {
 func Test_AssertEqInt(a: int, b: int) {
    if a != b {
-        PrintLine("ASSERT_EQ FAILED:");
+        PrintLine("ASSERT_EQ_INT FAILED:");
        PrintInt(a);
        PrintLine(" != ");
        PrintInt(b);
@@ -22,6 +23,31 @@ func Test_AssertEqInt(a: int, b: int) {
    }
 }
 func Test_AssertNeqInt(a: int, b: int) {
    if a == b {
        PrintLine("ASSERT_NEQ_INT FAILED: both are");
        PrintInt(a);
        bux_exit(1);
    }
 }
 func Test_AssertEqString(a: String, b: String) {
    if !String_Eq(a, b) {
        PrintLine("ASSERT_EQ_STRING FAILED:");
        PrintLine(a);
        PrintLine(" != ");
        PrintLine(b);
        bux_exit(1);
    }
 }
 func Test_AssertEqBool(a: bool, b: bool) {
    if a != b {
        PrintLine("ASSERT_EQ_BOOL FAILED");
        bux_exit(1);
    }
 }
 func Test_AssertTrue(cond: bool) {
    if !cond {
        PrintLine("ASSERT_TRUE FAILED");
@@ -42,4 +68,9 @@ func Test_Fail(msg: String) {
    bux_exit(1);
 }
 func Test_Pass(msg: String) {
    PrintLine("PASS:");
    PrintLine(msg);
 }
 }
@@ -143,6 +143,64 @@ int64_t bux_mod_i64(int64_t a, int64_t b) {
    return a % b;
 }
 /* Integer overflow checks (debug mode) */
 int64_t bux_add_i64_checked(int64_t a, int64_t b) {
 #if defined(__GNUC__) || defined(__clang__)
    int64_t result;
    if (__builtin_add_overflow(a, b, &result)) {
        bux_panic("integer overflow in addition");
    }
    return result;
 #else
    if ((b > 0 && a > INT64_MAX - b) || (b < 0 && a < INT64_MIN - b)) {
        bux_panic("integer overflow in addition");
    }
    return a + b;
 #endif
 }
 int64_t bux_sub_i64_checked(int64_t a, int64_t b) {
 #if defined(__GNUC__) || defined(__clang__)
    int64_t result;
    if (__builtin_sub_overflow(a, b, &result)) {
        bux_panic("integer overflow in subtraction");
    }
    return result;
 #else
    if ((b > 0 && a < INT64_MIN + b) || (b < 0 && a > INT64_MAX + b)) {
        bux_panic("integer overflow in subtraction");
    }
    return a - b;
 #endif
 }
 int64_t bux_mul_i64_checked(int64_t a, int64_t b) {
 #if defined(__GNUC__) || defined(__clang__)
    int64_t result;
    if (__builtin_mul_overflow(a, b, &result)) {
        bux_panic("integer overflow in multiplication");
    }
    return result;
 #else
    if (a != 0 && b != 0) {
        if ((a > 0 && b > 0 && a > INT64_MAX / b) ||
            (a > 0 && b < 0 && b < INT64_MIN / a) ||
            (a < 0 && b > 0 && a < INT64_MIN / b) ||
            (a < 0 && b < 0 && a < INT64_MAX / b)) {
            bux_panic("integer overflow in multiplication");
        }
    }
    return a * b;
 #endif
 }
 int64_t bux_neg_i64_checked(int64_t a) {
    if (a == INT64_MIN) {
        bux_panic("integer overflow in negation");
    }
    return -a;
 }
 /* String operations */
 typedef struct {
    const char* data;
@@ -189,6 +247,15 @@ void bux_bounds_check(size_t index, size_t len) {
    }
 }
 /* Bounds check that returns the index (usable in expressions) */
 size_t bux_index_check(size_t index, size_t len) {
    if (index >= len) {
        fprintf(stderr, "bux panic: index out of bounds (index %zu, len %zu)\n", index, len);
        abort();
    }
    return index;
 }
 /* String wrappers with Bux-compatible signatures */
 unsigned int bux_strlen(const char* s) {
    return (unsigned int)strlen(s);
@@ -8,30 +8,9 @@ module CBackend {
 // ---------------------------------------------------------------------------
 func CBackend_TypeToC(kind: int) -> String {
-    if kind == tyVoid { return "void"; }
+    let cName: String = Type_ToCName(kind);
-    if kind == tyBool { return "bool"; }
+    if !String_Eq(cName, "") { return cName; }
    if kind == tyBool8 { return "bool"; }
    if kind == tyBool16 { return "bool"; }
    if kind == tyBool32 { return "bool"; }
    if kind == tyChar8 { return "char"; }
    if kind == tyChar16 { return "uint16"; }
    if kind == tyChar32 { return "uint32"; }
    if kind == tyStr { return "String"; }
    if kind == tyInt8 { return "int8"; }
    if kind == tyInt16 { return "int16"; }
    if kind == tyInt32 { return "int32"; }
    if kind == tyInt64 { return "int64"; }
    if kind == tyInt{ return "int"; }
    if kind == tyUInt8 { return "uint8"; }
    if kind == tyUInt16 { return "uint16"; }
    if kind == tyUInt32 { return "uint32"; }
    if kind == tyUInt64 { return "uint64"; }
    if kind == tyUInt { return "uint"; }
    if kind == tyFloat32 { return "float32"; }
    if kind == tyFloat64 { return "float64"; }
    if kind == tyPointer { return "void*"; }
    if kind == tyNamed { return "int"; }
    if kind == tyFunc { return "void (*)(void)"; }
    return "int";
 }
@@ -338,31 +317,27 @@ func CBE_EmitExpr(cbe: *CEmitter, node: *HirNode) {
        return;
    }
-    // Indirect call through function pointer
+    // Indirect call through fat function pointer: f.code(f.env, args...)
    if kind == hCallIndirect {
        CBE_EmitExpr(cbe, node.child1);
        StringBuilder_Append(&cbe.sb, "(");
-        var needsComma: bool = false;
+        CBE_EmitExpr(cbe, node.child1);
        StringBuilder_Append(&cbe.sb, ".code)(");
        CBE_EmitExpr(cbe, node.child1);
        StringBuilder_Append(&cbe.sb, ".env");
        if node.child2 != null as *HirNode {
            StringBuilder_Append(&cbe.sb, ", ");
            CBE_EmitExpr(cbe, node.child2);
            needsComma = true;
        }
        if node.child3 != null as *HirNode {
-            if needsComma {
+            StringBuilder_Append(&cbe.sb, ", ");
                StringBuilder_Append(&cbe.sb, ", ");
            }
            CBE_EmitExpr(cbe, node.child3);
            needsComma = true;
        }
        // Emit extra args from linked list
        var ai: int = 0;
        var curExtra: *HirArgList = node.extraData as *HirArgList;
        while ai < node.extraCount {
-            if needsComma {
+            StringBuilder_Append(&cbe.sb, ", ");
                StringBuilder_Append(&cbe.sb, ", ");
            }
            CBE_EmitExpr(cbe, curExtra.node);
            needsComma = true;
            curExtra = curExtra.next;
            ai = ai + 1;
        }
@@ -590,11 +565,27 @@ func CBE_EmitExpr(cbe: *CEmitter, node: *HirNode) {
    }
    // Index: arr[idx] — emit as arr[idx]
    // For Array<T> desugar pattern (fieldPtr "data"), emit bounds-checked access
    if kind == hIndexPtr {
-        CBE_EmitExpr(cbe, node.child1);
+        var isArrayAccess: bool = false;
-        StringBuilder_Append(&cbe.sb, "[");
+        if node.child1 != null as *HirNode {
-        CBE_EmitExpr(cbe, node.child2);
+            if node.child1.kind == hFieldPtr && String_Eq(node.child1.strValue, "data") {
-        StringBuilder_Append(&cbe.sb, "]");
+                isArrayAccess = true;
            }
        }
        if isArrayAccess {
            CBE_EmitExpr(cbe, node.child1.child1);
            StringBuilder_Append(&cbe.sb, ".data[bux_index_check(");
            CBE_EmitExpr(cbe, node.child2);
            StringBuilder_Append(&cbe.sb, ", ");
            CBE_EmitExpr(cbe, node.child1.child1);
            StringBuilder_Append(&cbe.sb, ".len)]");
        } else {
            CBE_EmitExpr(cbe, node.child1);
            StringBuilder_Append(&cbe.sb, "[");
            CBE_EmitExpr(cbe, node.child2);
            StringBuilder_Append(&cbe.sb, "]");
        }
        return;
    }
@@ -629,19 +620,28 @@ func CBE_EmitExpr(cbe: *CEmitter, node: *HirNode) {
                StringBuilder_Append(&cbe.sb, ptrNode.strValue);
                return;
            }
            // arrow field: load(arrow_field(base, field)) → base->field
            if ptrKind == hArrowField {
                CBE_EmitExpr(cbe, ptrNode.child1);
                StringBuilder_Append(&cbe.sb, "->");
                StringBuilder_Append(&cbe.sb, ptrNode.strValue);
                return;
            }
            // index: load(index_ptr(base, idx)) → base[idx]
            // For Array<T> desugar pattern, emit bounds-checked access
            if ptrKind == hIndexPtr {
-                CBE_EmitExpr(cbe, ptrNode.child1);
+                var isArrayAccess: bool = false;
-                StringBuilder_Append(&cbe.sb, "[");
+                if ptrNode.child1 != null as *HirNode {
-                CBE_EmitExpr(cbe, ptrNode.child2);
+                    if ptrNode.child1.kind == hFieldPtr && String_Eq(ptrNode.child1.strValue, "data") {
-                StringBuilder_Append(&cbe.sb, "]");
+                        isArrayAccess = true;
                    }
                }
                if isArrayAccess {
                    CBE_EmitExpr(cbe, ptrNode.child1.child1);
                    StringBuilder_Append(&cbe.sb, ".data[bux_index_check(");
                    CBE_EmitExpr(cbe, ptrNode.child2);
                    StringBuilder_Append(&cbe.sb, ", ");
                    CBE_EmitExpr(cbe, ptrNode.child1.child1);
                    StringBuilder_Append(&cbe.sb, ".len)]");
                } else {
                    CBE_EmitExpr(cbe, ptrNode.child1);
                    StringBuilder_Append(&cbe.sb, "[");
                    CBE_EmitExpr(cbe, ptrNode.child2);
                    StringBuilder_Append(&cbe.sb, "]");
                }
                return;
            }
        }
@@ -727,6 +727,312 @@ func CBE_EmitExpr(cbe: *CEmitter, node: *HirNode) {
 // Emit function declaration
 // ---------------------------------------------------------------------------
 // Infer C type for a BuxFn mangled part (int, cstr, uint, void, ...)
 func CBE_FatPartToC(part: String) -> String {
    if String_Eq(part, "cstr") { return "const char*"; }
    if String_Eq(part, "void") { return "void"; }
    if String_Eq(part, "bool") { return "bool"; }
    if String_Eq(part, "uint") { return "unsigned int"; }
    if String_Eq(part, "float") { return "float"; }
    if String_Eq(part, "double") || String_Eq(part, "float64") { return "double"; }
    if String_EndsWith(part, "Ptr") {
        let base: String = String_Slice(part, 0, String_Len(part) - 3);
        return String_Concat(CBE_FatPartToC(base), "*");
    }
    return part; // int, etc.
 }
 // Emit typedefs for common BuxFn_* shapes (fat function pointers)
 func CBE_EmitFatFuncTypedefs(cbe: *CEmitter, mod: *HirModule) {
    StringBuilder_Append(&cbe.sb, "/* Fat function pointer types (code + env) */\n");
    // (int)->int
    StringBuilder_Append(&cbe.sb, "typedef struct BuxFn_int_int {\n");
    StringBuilder_Append(&cbe.sb, "    int (*code)(void* env, int a0);\n");
    StringBuilder_Append(&cbe.sb, "    void* env;\n");
    StringBuilder_Append(&cbe.sb, "} BuxFn_int_int;\n");
    // (int,int)->int
    StringBuilder_Append(&cbe.sb, "typedef struct BuxFn_int_int_int {\n");
    StringBuilder_Append(&cbe.sb, "    int (*code)(void* env, int a0, int a1);\n");
    StringBuilder_Append(&cbe.sb, "    void* env;\n");
    StringBuilder_Append(&cbe.sb, "} BuxFn_int_int_int;\n");
    // ()->void
    StringBuilder_Append(&cbe.sb, "typedef struct BuxFn_void_void {\n");
    StringBuilder_Append(&cbe.sb, "    void (*code)(void* env);\n");
    StringBuilder_Append(&cbe.sb, "    void* env;\n");
    StringBuilder_Append(&cbe.sb, "} BuxFn_void_void;\n");
    // ()->int
    StringBuilder_Append(&cbe.sb, "typedef struct BuxFn_int_void {\n");
    StringBuilder_Append(&cbe.sb, "    int (*code)(void* env);\n");
    StringBuilder_Append(&cbe.sb, "    void* env;\n");
    StringBuilder_Append(&cbe.sb, "} BuxFn_int_void;\n");
    // Scan module for any other BuxFn_* names
    var i: int = 0;
    while i < mod.funcCount {
        CBE_MaybeEmitExtraFat(cbe, mod.funcs[i].retTypeName);
        var p: int = 0;
        while p < mod.funcs[i].paramCount {
            var ptype: String = "";
            if p == 0 { ptype = mod.funcs[i].param0.typeName; }
            else if p == 1 { ptype = mod.funcs[i].param1.typeName; }
            else if p == 2 { ptype = mod.funcs[i].param2.typeName; }
            else if p == 3 { ptype = mod.funcs[i].param3.typeName; }
            else if p == 4 { ptype = mod.funcs[i].param4.typeName; }
            else if p == 5 { ptype = mod.funcs[i].param5.typeName; }
            else if p == 6 { ptype = mod.funcs[i].param6.typeName; }
            else if p == 7 { ptype = mod.funcs[i].param7.typeName; }
            else if p == 8 { ptype = mod.funcs[i].param8.typeName; }
            CBE_MaybeEmitExtraFat(cbe, ptype);
            p = p + 1;
        }
        i = i + 1;
    }
    StringBuilder_Append(&cbe.sb, "\n");
 }
 func CBE_MaybeEmitExtraFat(cbe: *CEmitter, name: String) {
    if String_Eq(name, "") { return; }
    if !String_StartsWith(name, "BuxFn_") { return; }
    // Skip ones we already emit as built-ins
    if String_Eq(name, "BuxFn_int_int") { return; }
    if String_Eq(name, "BuxFn_int_int_int") { return; }
    if String_Eq(name, "BuxFn_void_void") { return; }
    if String_Eq(name, "BuxFn_int_void") { return; }
    CBE_EmitOneFatTypedef(cbe, name);
 }
 func CBE_CollectBuxFn(names: *String, count: *int, name: String) {
    if String_Eq(name, "") { return; }
    if !String_StartsWith(name, "BuxFn_") { return; }
    if *count >= 64 { return; }
    var i: int = 0;
    while i < *count {
        if String_Eq(names[i], name) { return; }
        i = i + 1;
    }
    names[*count] = name;
    *count = *count + 1;
 }
 // BuxFn_ret_p0_p1 → typedef with code pointer
 func CBE_EmitOneFatTypedef(cbe: *CEmitter, fatName: String) {
    // Split fatName after "BuxFn_" into parts by '_'
    let prefixLen: uint = 6; // "BuxFn_"
    let rest: String = String_Slice(fatName, prefixLen, String_Len(fatName) - prefixLen);
    // Parse parts: first = ret, rest = params (use simple split)
    let partCount: uint = String_SplitCount(rest, "_");
    if partCount == 0 { return; }
    let retPart: String = String_SplitPart(rest, "_", 0);
    let retC: String = CBE_FatPartToC(retPart);
    StringBuilder_Append(&cbe.sb, "typedef struct ");
    StringBuilder_Append(&cbe.sb, fatName);
    StringBuilder_Append(&cbe.sb, " {\n    ");
    // code field: ret (*code)(void* env, params...)
    StringBuilder_Append(&cbe.sb, retC);
    StringBuilder_Append(&cbe.sb, " (*code)(void* env");
    var pi: uint = 1;
    while pi < partCount {
        let pPart: String = String_SplitPart(rest, "_", pi);
        if !(pi == 1 && String_Eq(pPart, "void") && partCount == 2) {
            StringBuilder_Append(&cbe.sb, ", ");
            StringBuilder_Append(&cbe.sb, CBE_FatPartToC(pPart));
        }
        pi = pi + 1;
    }
    StringBuilder_Append(&cbe.sb, ");\n    void* env;\n} ");
    StringBuilder_Append(&cbe.sb, fatName);
    StringBuilder_Append(&cbe.sb, ";\n");
 }
 func CBE_EmitMakerDecl(cbe: *CEmitter, f: *HirFunc) {
    // Infer fat type from thunk: skip __env, use user params + ret
    var fatName: String = "BuxFn_";
    var retC: String = f.retTypeName;
    if String_Eq(retC, "") { retC = "int"; }
    fatName = String_Concat(fatName, Lcx_SanitizeFatPart(retC));
    var pi: int = 1; // skip __env
    while pi < f.paramCount {
        var ptype: String = "int";
        if pi == 1 { ptype = f.param1.typeName; }
        else if pi == 2 { ptype = f.param2.typeName; }
        else if pi == 3 { ptype = f.param3.typeName; }
        else if pi == 4 { ptype = f.param4.typeName; }
        else if pi == 5 { ptype = f.param5.typeName; }
        else if pi == 6 { ptype = f.param6.typeName; }
        else if pi == 7 { ptype = f.param7.typeName; }
        else if pi == 8 { ptype = f.param8.typeName; }
        if String_Eq(ptype, "") { ptype = "int"; }
        fatName = String_Concat(fatName, "_");
        fatName = String_Concat(fatName, Lcx_SanitizeFatPart(ptype));
        pi = pi + 1;
    }
    if f.paramCount <= 1 {
        fatName = String_Concat(fatName, "_void");
    }
    StringBuilder_Append(&cbe.sb, fatName);
    StringBuilder_Append(&cbe.sb, " __make_");
    StringBuilder_Append(&cbe.sb, f.name);
    StringBuilder_Append(&cbe.sb, "(");
    var ci: int = 0;
    while ci < f.captureCount {
        if ci > 0 { StringBuilder_Append(&cbe.sb, ", "); }
        var capType: String = "int";
        var capName: String = "c";
        if ci == 0 { capName = f.captureName0; capType = CBackend_TypeToC(f.captureType0); }
        else if ci == 1 { capName = f.captureName1; capType = CBackend_TypeToC(f.captureType1); }
        else if ci == 2 { capName = f.captureName2; capType = CBackend_TypeToC(f.captureType2); }
        else if ci == 3 { capName = f.captureName3; capType = CBackend_TypeToC(f.captureType3); }
        else if ci == 4 { capName = f.captureName4; capType = CBackend_TypeToC(f.captureType4); }
        else if ci == 5 { capName = f.captureName5; capType = CBackend_TypeToC(f.captureType5); }
        else if ci == 6 { capName = f.captureName6; capType = CBackend_TypeToC(f.captureType6); }
        else if ci == 7 { capName = f.captureName7; capType = CBackend_TypeToC(f.captureType7); }
        StringBuilder_Append(&cbe.sb, capType);
        StringBuilder_Append(&cbe.sb, " ");
        StringBuilder_Append(&cbe.sb, capName);
        ci = ci + 1;
    }
    StringBuilder_Append(&cbe.sb, ")");
 }
 func CBE_EmitMakerFunc(cbe: *CEmitter, f: *HirFunc) {
    CBE_EmitMakerDecl(cbe, f);
    StringBuilder_Append(&cbe.sb, " {\n");
    StringBuilder_Append(&cbe.sb, "    ");
    StringBuilder_Append(&cbe.sb, f.envStructName);
    StringBuilder_Append(&cbe.sb, "* __e = (");
    StringBuilder_Append(&cbe.sb, f.envStructName);
    StringBuilder_Append(&cbe.sb, "*)bux_alloc(sizeof(");
    StringBuilder_Append(&cbe.sb, f.envStructName);
    StringBuilder_Append(&cbe.sb, "));\n");
    var ci: int = 0;
    while ci < f.captureCount {
        var capName: String = "";
        if ci == 0 { capName = f.captureName0; }
        else if ci == 1 { capName = f.captureName1; }
        else if ci == 2 { capName = f.captureName2; }
        else if ci == 3 { capName = f.captureName3; }
        else if ci == 4 { capName = f.captureName4; }
        else if ci == 5 { capName = f.captureName5; }
        else if ci == 6 { capName = f.captureName6; }
        else if ci == 7 { capName = f.captureName7; }
        StringBuilder_Append(&cbe.sb, "    __e->");
        StringBuilder_Append(&cbe.sb, capName);
        StringBuilder_Append(&cbe.sb, " = ");
        StringBuilder_Append(&cbe.sb, capName);
        StringBuilder_Append(&cbe.sb, ";\n");
        ci = ci + 1;
    }
    // Build fat return type name same as decl
    var fatName: String = "BuxFn_";
    var retC: String = f.retTypeName;
    if String_Eq(retC, "") { retC = "int"; }
    fatName = String_Concat(fatName, Lcx_SanitizeFatPart(retC));
    var pi: int = 1;
    while pi < f.paramCount {
        var ptype: String = "int";
        if pi == 1 { ptype = f.param1.typeName; }
        else if pi == 2 { ptype = f.param2.typeName; }
        else if pi == 3 { ptype = f.param3.typeName; }
        else if pi == 4 { ptype = f.param4.typeName; }
        else if pi == 5 { ptype = f.param5.typeName; }
        else if pi == 6 { ptype = f.param6.typeName; }
        else if pi == 7 { ptype = f.param7.typeName; }
        else if pi == 8 { ptype = f.param8.typeName; }
        if String_Eq(ptype, "") { ptype = "int"; }
        fatName = String_Concat(fatName, "_");
        fatName = String_Concat(fatName, Lcx_SanitizeFatPart(ptype));
        pi = pi + 1;
    }
    if f.paramCount <= 1 {
        fatName = String_Concat(fatName, "_void");
    }
    StringBuilder_Append(&cbe.sb, "    return (");
    StringBuilder_Append(&cbe.sb, fatName);
    StringBuilder_Append(&cbe.sb, "){ .code = ");
    StringBuilder_Append(&cbe.sb, f.name);
    StringBuilder_Append(&cbe.sb, ", .env = __e };\n}\n\n");
 }
 // Emit adapters for any non-closure function (used when taken as value)
 func CBE_EmitAllAdapters(cbe: *CEmitter, mod: *HirModule) {
    StringBuilder_Append(&cbe.sb, "/* Fat-func adapters for named functions */\n");
    var i: int = 0;
    while i < mod.funcCount {
        let fname: String = mod.funcs[i].name;
        // Skip closures, makers, adapters themselves
        if String_StartsWith(fname, "__closure_") || String_StartsWith(fname, "__make_") || String_StartsWith(fname, "__adapt_") {
            i = i + 1;
            continue;
        }
        if CBE_FuncHasGeneric(&mod.funcs[i]) {
            i = i + 1;
            continue;
        }
        // Only emit adapter if function has body
        if mod.funcs[i].body == null as *HirNode {
            i = i + 1;
            continue;
        }
        // Adapter signature: ret __adapt_F(void* env, params...) { return F(params); }
        var retC: String = mod.funcs[i].retTypeName;
        if String_Eq(retC, "") { retC = "void"; }
        StringBuilder_Append(&cbe.sb, "static ");
        StringBuilder_Append(&cbe.sb, retC);
        StringBuilder_Append(&cbe.sb, " __adapt_");
        StringBuilder_Append(&cbe.sb, fname);
        StringBuilder_Append(&cbe.sb, "(void* env");
        var p: int = 0;
        while p < mod.funcs[i].paramCount {
            // Skip if first param is already __env (shouldn't for named funcs)
            var pname: String = "";
            var ptype: String = "int";
            if p == 0 { pname = mod.funcs[i].param0.name; ptype = mod.funcs[i].param0.typeName; }
            else if p == 1 { pname = mod.funcs[i].param1.name; ptype = mod.funcs[i].param1.typeName; }
            else if p == 2 { pname = mod.funcs[i].param2.name; ptype = mod.funcs[i].param2.typeName; }
            else if p == 3 { pname = mod.funcs[i].param3.name; ptype = mod.funcs[i].param3.typeName; }
            else if p == 4 { pname = mod.funcs[i].param4.name; ptype = mod.funcs[i].param4.typeName; }
            else if p == 5 { pname = mod.funcs[i].param5.name; ptype = mod.funcs[i].param5.typeName; }
            else if p == 6 { pname = mod.funcs[i].param6.name; ptype = mod.funcs[i].param6.typeName; }
            else if p == 7 { pname = mod.funcs[i].param7.name; ptype = mod.funcs[i].param7.typeName; }
            else if p == 8 { pname = mod.funcs[i].param8.name; ptype = mod.funcs[i].param8.typeName; }
            if String_Eq(ptype, "") { ptype = "int"; }
            StringBuilder_Append(&cbe.sb, ", ");
            StringBuilder_Append(&cbe.sb, ptype);
            StringBuilder_Append(&cbe.sb, " ");
            StringBuilder_Append(&cbe.sb, pname);
            p = p + 1;
        }
        StringBuilder_Append(&cbe.sb, ") {\n    (void)env;\n");
        if String_Eq(retC, "void") {
            StringBuilder_Append(&cbe.sb, "    ");
            StringBuilder_Append(&cbe.sb, fname);
            StringBuilder_Append(&cbe.sb, "(");
        } else {
            StringBuilder_Append(&cbe.sb, "    return ");
            StringBuilder_Append(&cbe.sb, fname);
            StringBuilder_Append(&cbe.sb, "(");
        }
        p = 0;
        while p < mod.funcs[i].paramCount {
            if p > 0 { StringBuilder_Append(&cbe.sb, ", "); }
            var pname: String = "";
            if p == 0 { pname = mod.funcs[i].param0.name; }
            else if p == 1 { pname = mod.funcs[i].param1.name; }
            else if p == 2 { pname = mod.funcs[i].param2.name; }
            else if p == 3 { pname = mod.funcs[i].param3.name; }
            else if p == 4 { pname = mod.funcs[i].param4.name; }
            else if p == 5 { pname = mod.funcs[i].param5.name; }
            else if p == 6 { pname = mod.funcs[i].param6.name; }
            else if p == 7 { pname = mod.funcs[i].param7.name; }
            else if p == 8 { pname = mod.funcs[i].param8.name; }
            StringBuilder_Append(&cbe.sb, pname);
            p = p + 1;
        }
        StringBuilder_Append(&cbe.sb, ");\n}\n\n");
        i = i + 1;
    }
 }
 func CBE_EmitFuncDecl(cbe: *CEmitter, f: *HirFunc) {
    // Return type
    if String_Eq(f.retTypeName, "") || String_Eq(f.retTypeName, "void") {
@@ -961,7 +1267,12 @@ func CBackend_Generate(mod: *HirModule) -> String {
    StringBuilder_Append(&cbe.sb, "typedef char char8;\n\n");
    // Runtime declarations
    StringBuilder_Append(&cbe.sb, "void* bux_alloc(unsigned int size);\n");
-    StringBuilder_Append(&cbe.sb, "void bux_free(void* ptr);\n\n");
+    StringBuilder_Append(&cbe.sb, "void bux_free(void* ptr);\n");
    StringBuilder_Append(&cbe.sb, "unsigned long long bux_index_check(unsigned long long index, unsigned long long len);\n");
    StringBuilder_Append(&cbe.sb, "int64 bux_add_i64_checked(int64 a, int64 b);\n");
    StringBuilder_Append(&cbe.sb, "int64 bux_sub_i64_checked(int64 a, int64 b);\n");
    StringBuilder_Append(&cbe.sb, "int64 bux_mul_i64_checked(int64 a, int64 b);\n");
    StringBuilder_Append(&cbe.sb, "int64 bux_neg_i64_checked(int64 a);\n\n");
    // Forward declare all struct types (skip empty names)
    var si: int = 0;
@@ -1121,12 +1432,53 @@ func CBackend_Generate(mod: *HirModule) -> String {
        si = si + 1;
    }
    // Fat function-pointer typedefs (BuxFn_*) — before forward decls
    CBE_EmitFatFuncTypedefs(cbe, mod);
    // Env structs for capturing closures (no static instance — heap per value)
    var ei2: int = 0;
    while ei2 < mod.funcCount {
        if mod.funcs[ei2].captureCount > 0 && !String_Eq(mod.funcs[ei2].envStructName, "") {
            StringBuilder_Append(&cbe.sb, "typedef struct ");
            StringBuilder_Append(&cbe.sb, mod.funcs[ei2].envStructName);
            StringBuilder_Append(&cbe.sb, " {\n");
            var ci2: int = 0;
            while ci2 < mod.funcs[ei2].captureCount {
                var capName: String = "";
                var capType: String = "int";
                if ci2 == 0 { capName = mod.funcs[ei2].captureName0; capType = CBackend_TypeToC(mod.funcs[ei2].captureType0); }
                else if ci2 == 1 { capName = mod.funcs[ei2].captureName1; capType = CBackend_TypeToC(mod.funcs[ei2].captureType1); }
                else if ci2 == 2 { capName = mod.funcs[ei2].captureName2; capType = CBackend_TypeToC(mod.funcs[ei2].captureType2); }
                else if ci2 == 3 { capName = mod.funcs[ei2].captureName3; capType = CBackend_TypeToC(mod.funcs[ei2].captureType3); }
                else if ci2 == 4 { capName = mod.funcs[ei2].captureName4; capType = CBackend_TypeToC(mod.funcs[ei2].captureType4); }
                else if ci2 == 5 { capName = mod.funcs[ei2].captureName5; capType = CBackend_TypeToC(mod.funcs[ei2].captureType5); }
                else if ci2 == 6 { capName = mod.funcs[ei2].captureName6; capType = CBackend_TypeToC(mod.funcs[ei2].captureType6); }
                else if ci2 == 7 { capName = mod.funcs[ei2].captureName7; capType = CBackend_TypeToC(mod.funcs[ei2].captureType7); }
                StringBuilder_Append(&cbe.sb, "    ");
                StringBuilder_Append(&cbe.sb, capType);
                StringBuilder_Append(&cbe.sb, " ");
                StringBuilder_Append(&cbe.sb, capName);
                StringBuilder_Append(&cbe.sb, ";\n");
                ci2 = ci2 + 1;
            }
            StringBuilder_Append(&cbe.sb, "} ");
            StringBuilder_Append(&cbe.sb, mod.funcs[ei2].envStructName);
            StringBuilder_Append(&cbe.sb, ";\n\n");
        }
        ei2 = ei2 + 1;
    }
    // Forward declarations for all functions (skip generics)
    var i: int = 0;
    while i < mod.funcCount {
        if !CBE_FuncHasGeneric(&mod.funcs[i]) {
            CBE_EmitFuncDecl(cbe, &mod.funcs[i]);
            StringBuilder_Append(&cbe.sb, ";\n");
            // Maker for capturing closures
            if mod.funcs[i].captureCount > 0 {
                CBE_EmitMakerDecl(cbe, &mod.funcs[i]);
                StringBuilder_Append(&cbe.sb, ";\n");
            }
        }
        i = i + 1;
    }
@@ -1141,6 +1493,9 @@ func CBackend_Generate(mod: *HirModule) -> String {
    }
    StringBuilder_Append(&cbe.sb, "\n");
    // Adapters before function bodies (bodies may take funcs as values)
    CBE_EmitAllAdapters(cbe, mod);
    // Function definitions (skip generics)
    var hasMain: bool = false;
    i = 0;
@@ -1157,45 +1512,23 @@ func CBackend_Generate(mod: *HirModule) -> String {
            i = i + 1;
            continue;
        }
        // Emit env struct and global instance for closures with captures
        if mod.funcs[i].captureCount > 0 {
            let envName: String = mod.funcs[i].envStructName;
            let instName: String = mod.funcs[i].envInstanceName;
            if !String_Eq(envName, "") {
                // Emit struct definition
                StringBuilder_Append(&cbe.sb, "struct ");
                StringBuilder_Append(&cbe.sb, envName);
                StringBuilder_Append(&cbe.sb, " {\n");
                var ci: int = 0;
                while ci < mod.funcs[i].captureCount {
                    var capName: String = "";
                    var capType: String = "int";
                    if ci == 0 { capName = mod.funcs[i].captureName0; capType = CBackend_TypeToC(mod.funcs[i].captureType0); }
                    else if ci == 1 { capName = mod.funcs[i].captureName1; capType = CBackend_TypeToC(mod.funcs[i].captureType1); }
                    else if ci == 2 { capName = mod.funcs[i].captureName2; capType = CBackend_TypeToC(mod.funcs[i].captureType2); }
                    else if ci == 3 { capName = mod.funcs[i].captureName3; capType = CBackend_TypeToC(mod.funcs[i].captureType3); }
                    else if ci == 4 { capName = mod.funcs[i].captureName4; capType = CBackend_TypeToC(mod.funcs[i].captureType4); }
                    else if ci == 5 { capName = mod.funcs[i].captureName5; capType = CBackend_TypeToC(mod.funcs[i].captureType5); }
                    else if ci == 6 { capName = mod.funcs[i].captureName6; capType = CBackend_TypeToC(mod.funcs[i].captureType6); }
                    else if ci == 7 { capName = mod.funcs[i].captureName7; capType = CBackend_TypeToC(mod.funcs[i].captureType7); }
                    StringBuilder_Append(&cbe.sb, "    ");
                    StringBuilder_Append(&cbe.sb, capType);
                    StringBuilder_Append(&cbe.sb, " ");
                    StringBuilder_Append(&cbe.sb, capName);
                    StringBuilder_Append(&cbe.sb, ";\n");
                    ci = ci + 1;
                }
                StringBuilder_Append(&cbe.sb, "};\n");
                // Emit global instance
                StringBuilder_Append(&cbe.sb, "static struct ");
                StringBuilder_Append(&cbe.sb, envName);
                StringBuilder_Append(&cbe.sb, " ");
                StringBuilder_Append(&cbe.sb, instName);
                StringBuilder_Append(&cbe.sb, ";\n\n");
            }
        }
        CBE_EmitFuncDecl(cbe, &mod.funcs[i]);
        StringBuilder_Append(&cbe.sb, " {\n");
        // Capturing closure thunk: materialize env from fat-func env pointer
        if mod.funcs[i].captureCount > 0 && !String_Eq(mod.funcs[i].envStructName, "") && !String_Eq(mod.funcs[i].envInstanceName, "") {
            StringBuilder_Append(&cbe.sb, "    ");
            StringBuilder_Append(&cbe.sb, mod.funcs[i].envStructName);
            StringBuilder_Append(&cbe.sb, " ");
            StringBuilder_Append(&cbe.sb, mod.funcs[i].envInstanceName);
            StringBuilder_Append(&cbe.sb, " = *((");
            StringBuilder_Append(&cbe.sb, mod.funcs[i].envStructName);
            StringBuilder_Append(&cbe.sb, "*)__env);\n");
        } else if mod.funcs[i].paramCount > 0 {
            // Capture-less closure still has __env
            if String_Eq(mod.funcs[i].param0.name, "__env") {
                StringBuilder_Append(&cbe.sb, "    (void)__env;\n");
            }
        }
        // Body
        cbe.checkedFunc = mod.funcs[i].checkedFunc;
        cbe.deferCount = 0;
@@ -1216,6 +1549,10 @@ func CBackend_Generate(mod: *HirModule) -> String {
            StringBuilder_Append(&cbe.sb, "    return 0;\n");
        }
        StringBuilder_Append(&cbe.sb, "\n}\n\n");
        // After capturing closure thunk, emit heap-env maker
        if mod.funcs[i].captureCount > 0 {
            CBE_EmitMakerFunc(cbe, &mod.funcs[i]);
        }
        i = i + 1;
    }
@@ -55,12 +55,44 @@ func Diagnostic_GetLine(path: String, lineNum: uint32) -> String {
    return bux_str_split_part(content, "\n", lineNum - 1);
 }
 /* Simple substring check for help hints */
 func Diagnostic_MsgContains(msg: String, needle: String) -> bool {
    return bux_str_contains(msg, needle) != 0;
 }
 /* Actionable help for common error messages */
 func Diagnostic_Hint(msg: String) -> String {
    if Diagnostic_MsgContains(msg, "cannot assign") {
        return "ensure the right-hand side type matches the left-hand side";
    }
    if Diagnostic_MsgContains(msg, "undeclared identifier") {
        return "check the spelling, or import the symbol from the right module";
    }
    if Diagnostic_MsgContains(msg, "too few arguments") {
        return "compare the call with the function's parameter list";
    }
    if Diagnostic_MsgContains(msg, "too many arguments") {
        return "compare the call with the function's parameter list";
    }
    if Diagnostic_MsgContains(msg, "use of moved value") {
        return "the value was moved; clone it or restructure ownership";
    }
    if Diagnostic_MsgContains(msg, "expected expression") {
        return "the previous statement may be incomplete (missing value or ';')";
    }
    if Diagnostic_MsgContains(msg, "duplicate symbol") {
        return "rename one of the definitions or remove the duplicate";
    }
    return "";
 }
 /* Print a diagnostic in Rust-style format:
 *   error: <message>
 *     --> <path>:<line>:<col>
 *      |
 *   42 | <source_line>
 *      | <spaces>^
 *      = help: <hint>
 */
 func Diagnostic_Print(diag: *Diagnostic, sourcePath: String) {
    /* Severity prefix */
@@ -94,14 +126,57 @@ func Diagnostic_Print(diag: *Diagnostic, sourcePath: String) {
        Print(" | ");
        PrintLine(lineText);
-        /* Underline */
+        /* Underline (multi-char for identifiers/string tokens) */
        Print("   | ");
        var i: uint32 = 0;
        while i < diag.column - 1 && i < 120 {
            Print(" ");
            i = i + 1;
        }
-        PrintLine("^");
+        /* Estimate token length from the source line */
        var ulen: uint = 1;
        let col0: uint = diag.column - 1;
        let lineLen: uint = String_Len(lineText);
        if col0 < lineLen {
            let first: String = String_Chars(lineText, col0);
            if String_Eq(first, "\"") || String_Eq(first, "`") || String_Eq(first, "'") {
                var j: uint = col0 + 1;
                while j < lineLen {
                    let cj: String = String_Chars(lineText, j);
                    if String_Eq(cj, first) {
                        ulen = j - col0 + 1;
                        break;
                    }
                    j = j + 1;
                }
            } else {
                var j: uint = col0;
                while j < lineLen {
                    let cj: String = String_Chars(lineText, j);
                    if String_Contains("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_", cj) {
                        j = j + 1;
                    } else {
                        break;
                    }
                }
                if j > col0 {
                    ulen = j - col0;
                }
            }
        }
        var k: uint = 0;
        while k < ulen {
            Print("^");
            k = k + 1;
        }
        PrintLine("");
    }
    /* Helpful hint when we recognize the error */
    let hint: String = Diagnostic_Hint(diag.message);
    if !String_Eq(hint, "") {
        Print("   = help: ");
        PrintLine(hint);
    }
 }
@@ -43,30 +43,7 @@ struct LowerCtx {
 // ---------------------------------------------------------------------------
 func Lcx_ResolveTypeKindFromName(name: String) -> int {
-    if String_Eq(name, "void") { return tyVoid; }
+    return Type_FromName(name);
    if String_Eq(name, "bool") { return tyBool; }
    if String_Eq(name, "bool8") { return tyBool8; }
    if String_Eq(name, "bool16") { return tyBool16; }
    if String_Eq(name, "bool32") { return tyBool32; }
    if String_Eq(name, "char8") { return tyChar8; }
    if String_Eq(name, "char16") { return tyChar16; }
    if String_Eq(name, "char32") { return tyChar32; }
    if String_Eq(name, "String") { return tyStr; }
    if String_Eq(name, "str") { return tyStr; }
    if String_Eq(name, "int8") { return tyInt8; }
    if String_Eq(name, "int16") { return tyInt16; }
    if String_Eq(name, "int32") { return tyInt32; }
    if String_Eq(name, "int64") { return tyInt64; }
    if String_Eq(name, "int") { return tyInt; }
    if String_Eq(name, "uint8") { return tyUInt8; }
    if String_Eq(name, "uint16") { return tyUInt16; }
    if String_Eq(name, "uint32") { return tyUInt32; }
    if String_Eq(name, "uint64") { return tyUInt64; }
    if String_Eq(name, "uint") { return tyUInt; }
    if String_Eq(name, "float32") { return tyFloat32; }
    if String_Eq(name, "float64") { return tyFloat64; }
    if String_Eq(name, "float") { return tyFloat64; }
    return tyNamed;
 }
 func Lcx_TypeKindToName(kind: int) -> String {
@@ -178,38 +155,58 @@ func Lcx_SubstituteType(ctx: *LowerCtx, te: *TypeExpr) -> *TypeExpr {
    return te;
 }
-// Build C function-pointer type string from a tekFunc TypeExpr, e.g. "int (*)(int)"
+// Sanitize a C type fragment for use inside BuxFn_* mangled names
-func Lcx_BuildFuncTypeName(te: *TypeExpr) -> String {
+func Lcx_SanitizeFatPart(s: String) -> String {
-    if te == null as *TypeExpr || te.kind != tekFunc { return "void (*)(void)"; }
+    var r: String = s;
-    var retName: String = "void";
+    if String_Eq(r, "String") || String_Eq(r, "str") || String_Eq(r, "const char*") {
-    if te.funcRet != null as *TypeExpr {
+        return "cstr";
        if te.funcRet.kind == tekPointer && te.funcRet.pointerPointee != null as *TypeExpr {
            retName = String_Concat(te.funcRet.pointerPointee.typeName, "*");
        } else {
            retName = te.funcRet.typeName;
        }
        if String_Eq(retName, "") { retName = "int"; }
    }
-    var result: String = retName;
+    if String_Eq(r, "unsigned int") { return "uint"; }
-    result = String_Concat(result, " (*)(");
+    // crude replacements for * and spaces
    r = String_ReplaceAll(r, "*", "Ptr");
    r = String_ReplaceAll(r, " ", "_");
    r = String_ReplaceAll(r, "(", "");
    r = String_ReplaceAll(r, ")", "");
    r = String_ReplaceAll(r, ",", "_");
    if String_Eq(r, "") { return "int"; }
    return r;
 }
 func Lcx_TypeExprFatPart(te: *TypeExpr) -> String {
    if te == null as *TypeExpr { return "void"; }
    if te.kind == tekPointer && te.pointerPointee != null as *TypeExpr {
        return Lcx_SanitizeFatPart(String_Concat(te.pointerPointee.typeName, "Ptr"));
    }
    if te.kind == tekFunc {
        return Lcx_SanitizeFatPart(Lcx_BuildFuncTypeName(te));
    }
    var n: String = te.typeName;
    if String_Eq(n, "") { n = "int"; }
    return Lcx_SanitizeFatPart(n);
 }
 // Fat function-pointer type name: BuxFn_<ret>_<p0>_<p1>...
 // Enables multi-instance closures (code + env).
 func Lcx_BuildFuncTypeName(te: *TypeExpr) -> String {
    if te == null as *TypeExpr || te.kind != tekFunc {
        return "BuxFn_void_void";
    }
    var retPart: String = "void";
    if te.funcRet != null as *TypeExpr {
        retPart = Lcx_TypeExprFatPart(te.funcRet);
    }
    var result: String = String_Concat("BuxFn_", retPart);
    var cur: *TypeExprList = te.funcParams;
-    var first: bool = true;
+    var anyParam: bool = false;
    while cur != null as *TypeExprList {
-        if !first {
+        result = String_Concat(result, "_");
-            result = String_Concat(result, ", ");
+        result = String_Concat(result, Lcx_TypeExprFatPart(cur.te));
-        }
+        anyParam = true;
        var pName: String = "int";
        if cur.te.kind == tekPointer && cur.te.pointerPointee != null as *TypeExpr {
            pName = String_Concat(cur.te.pointerPointee.typeName, "*");
        } else {
            pName = cur.te.typeName;
        }
        if String_Eq(pName, "") { pName = "int"; }
        result = String_Concat(result, pName);
        first = false;
        cur = cur.next;
    }
-    result = String_Concat(result, ")");
+    if !anyParam {
        result = String_Concat(result, "_void");
    }
    return result;
 }
@@ -469,9 +466,44 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
                return n;
            }
        }
        let sym: Symbol = Scope_Lookup(ctx.scope, expr.strValue);
        // Named function used as a value → fat pointer via __adapt_ wrapper
        if sym.kind == skFunc {
            var fatName: String = "BuxFn_int_int";
            if sym.refType != null as *TypeExpr && sym.refType.kind == tekFunc {
                fatName = Lcx_BuildFuncTypeName(sym.refType);
            } else if !String_Eq(sym.typeName, "") && String_StartsWith(sym.typeName, "BuxFn_") {
                fatName = sym.typeName;
            }
            n.kind = hStructInit;
            n.strValue = fatName;
            n.typeKind = tyFunc;
            n.typeName = fatName;
            let codeField: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            codeField.kind = hBlock;
            codeField.strValue = "code";
            let codeVal: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            codeVal.kind = hVar;
            codeVal.strValue = String_Concat("__adapt_", expr.strValue);
            codeField.child1 = codeVal;
            let envField: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            envField.kind = hBlock;
            envField.strValue = "env";
            let nullEnv: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            nullEnv.kind = hCast;
            nullEnv.typeName = "void*";
            let zero: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            zero.kind = hLit;
            zero.intValue = tkIntLiteral;
            zero.strValue = "0";
            nullEnv.child1 = zero;
            envField.child1 = nullEnv;
            codeField.child3 = envField;
            n.child1 = codeField;
            return n;
        }
        n.kind = hVar;
        n.strValue = expr.strValue;
        let sym: Symbol = Scope_Lookup(ctx.scope, expr.strValue);
        n.typeKind = sym.typeKind;
        if expr.refType != null as *TypeExpr {
@@ -566,6 +598,30 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
            }
        }
        // Overflow checking: in @[Checked] mode, lower +, -, * on signed integers to checked calls
        if ctx.checkedFunc && !ctx.releaseFunc {
            var opKind: int = expr.intValue;
            var isArithOp: bool = opKind == tkPlus || opKind == tkMinus || opKind == tkStar;
            var isSignedInt: bool = false;
            if expr.child1 != null as *Expr && expr.child1.refType != null as *TypeExpr {
                let lhsKind: int = Lcx_ResolveTypeKind(expr.child1.refType);
                isSignedInt = Type_IsSigned(lhsKind);
            }
            if isArithOp && isSignedInt {
                var checkedFunc: String = "";
                if opKind == tkPlus { checkedFunc = "bux_add_i64_checked"; }
                else if opKind == tkMinus { checkedFunc = "bux_sub_i64_checked"; }
                else if opKind == tkStar { checkedFunc = "bux_mul_i64_checked"; }
                if !String_Eq(checkedFunc, "") {
                    n.kind = hCall;
                    n.strValue = checkedFunc;
                    n.child1 = Lcx_LowerExpr(ctx, expr.child1);
                    n.child2 = Lcx_LowerExpr(ctx, expr.child2);
                    return n;
                }
            }
        }
        n.kind = hBinary;
        n.intValue = expr.intValue; // operator
        n.child1 = Lcx_LowerExpr(ctx, expr.child1);
@@ -575,6 +631,20 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
    // Unary
    if kind == ekUnary {
        // Overflow checking: in @[Checked] mode, lower negation on signed integers to checked call
        if ctx.checkedFunc && !ctx.releaseFunc && expr.intValue == tkMinus {
            var isSignedInt: bool = false;
            if expr.child1 != null as *Expr && expr.child1.refType != null as *TypeExpr {
                let operandKind: int = Lcx_ResolveTypeKind(expr.child1.refType);
                isSignedInt = Type_IsSigned(operandKind);
            }
            if isSignedInt {
                n.kind = hCall;
                n.strValue = "bux_neg_i64_checked";
                n.child1 = Lcx_LowerExpr(ctx, expr.child1);
                return n;
            }
        }
        n.kind = hUnary;
        n.intValue = expr.intValue;
        n.child1 = Lcx_LowerExpr(ctx, expr.child1);
@@ -1132,20 +1202,85 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
        return n;
    }
-    // Closure: generate function and return address-of
+    // Closure: fat function pointer (multi-instance via heap env + maker)
    if kind == ekClosure {
        let f: *HirFunc = Lcx_LowerClosureFunc(ctx, expr);
-        n.kind = hUnary;
+        var fatName: String = "BuxFn_int_int";
-        n.intValue = tkAmp;
+        if expr.refType != null as *TypeExpr && expr.refType.kind == tekFunc {
-        let varNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            fatName = Lcx_BuildFuncTypeName(expr.refType);
-        varNode.kind = hVar;
+        } else if f.paramCount >= 2 {
-        varNode.strValue = f.name;
+            // thunk has __env + user params; approximate from ret + user arity
-        varNode.typeKind = tyFunc;
+            fatName = "BuxFn_int_int";
-        n.child1 = varNode;
+            if f.paramCount == 3 { fatName = "BuxFn_int_int_int"; }
-        n.typeKind = tyFunc;
+            if f.paramCount == 1 { fatName = "BuxFn_int_void"; }
        if expr.refType != null as *TypeExpr {
            n.typeName = Lcx_BuildFuncTypeName(expr.refType);
        }
        if f.captureCount > 0 {
            // Call __make_<closure>(captures...) which heap-allocs env
            n.kind = hCall;
            n.strValue = String_Concat("__make_", f.name);
            n.typeKind = tyFunc;
            n.typeName = fatName;
            var ci: int = 0;
            while ci < f.captureCount {
                var capName: String = "";
                if ci == 0 { capName = f.captureName0; }
                else if ci == 1 { capName = f.captureName1; }
                else if ci == 2 { capName = f.captureName2; }
                else if ci == 3 { capName = f.captureName3; }
                else if ci == 4 { capName = f.captureName4; }
                else if ci == 5 { capName = f.captureName5; }
                else if ci == 6 { capName = f.captureName6; }
                else if ci == 7 { capName = f.captureName7; }
                let capVar: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
                capVar.kind = hVar;
                capVar.strValue = capName;
                if ci == 0 { n.child1 = capVar; }
                else if ci == 1 { n.child2 = capVar; }
                else if ci == 2 {
                    let firstExtra: *HirArgList = bux_alloc(sizeof(HirArgList)) as *HirArgList;
                    firstExtra.node = capVar;
                    firstExtra.next = null as *HirArgList;
                    n.extraData = firstExtra as *void;
                    n.extraCount = 1;
                } else {
                    var cur: *HirArgList = n.extraData as *HirArgList;
                    while cur.next != null as *HirArgList { cur = cur.next; }
                    let newNode: *HirArgList = bux_alloc(sizeof(HirArgList)) as *HirArgList;
                    newNode.node = capVar;
                    newNode.next = null as *HirArgList;
                    cur.next = newNode;
                    n.extraCount = n.extraCount + 1;
                }
                ci = ci + 1;
            }
            return n;
        }
        // Capture-less: compound literal fat pointer with NULL env
        n.kind = hStructInit;
        n.strValue = fatName;
        n.typeKind = tyFunc;
        n.typeName = fatName;
        let codeField: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
        codeField.kind = hBlock;
        codeField.strValue = "code";
        let codeVal: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
        codeVal.kind = hVar;
        codeVal.strValue = f.name;
        codeField.child1 = codeVal;
        let envField: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
        envField.kind = hBlock;
        envField.strValue = "env";
        let nullEnv: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
        nullEnv.kind = hCast;
        nullEnv.typeName = "void*";
        let zero: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
        zero.kind = hLit;
        zero.intValue = tkIntLiteral;
        zero.strValue = "0";
        nullEnv.child1 = zero;
        envField.child1 = nullEnv;
        codeField.child3 = envField;
        n.child1 = codeField;
        return n;
    }
@@ -1227,6 +1362,25 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
        return n;
    }
    // Block expression (boolValue = true means unsafe block)
    if kind == ekBlock {
        if expr.refBlock != null as *Block {
            if expr.boolValue {
                let oldChecked: bool = ctx.checkedFunc;
                let oldRelease: bool = ctx.releaseFunc;
                ctx.checkedFunc = false;
                ctx.releaseFunc = false;
                let blockNode: *HirNode = Lcx_LowerBlock(ctx, expr.refBlock, -1);
                ctx.checkedFunc = oldChecked;
                ctx.releaseFunc = oldRelease;
                return blockNode;
            } else {
                return Lcx_LowerBlock(ctx, expr.refBlock, -1);
            }
        }
        return n;
    }
    return n;
 }
@@ -1461,71 +1615,8 @@ func Lcx_LowerStmt(ctx: *LowerCtx, stmt: *Stmt) -> *HirNode {
            }
        }
-        // If init is a closure with captures, emit capture assignments before the let
+        // Capturing closures allocate env via __make_* at ekClosure site.
-        if stmt.child1 != null as *Expr && stmt.child1.kind == ekClosure && stmt.child1.captureCount > 0 {
+        // Wrap with defer if present
            let closureIdx: int = ctx.funcCount - 1;
            let envInst: String = String_Concat("__closure_env_instance_", String_FromInt(closureIdx));
            // Build a block: capture assignments + let store
            let blockNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
            blockNode.kind = hBlock;
            blockNode.line = line;
            blockNode.column = col;
            var firstStmt: *HirNode = null as *HirNode;
            var lastStmt: *HirNode = null as *HirNode;
            var ci: int = 0;
            while ci < stmt.child1.captureCount {
                var capName: String = "";
                if ci == 0 { capName = stmt.child1.captureName0; }
                else if ci == 1 { capName = stmt.child1.captureName1; }
                else if ci == 2 { capName = stmt.child1.captureName2; }
                else if ci == 3 { capName = stmt.child1.captureName3; }
                else if ci == 4 { capName = stmt.child1.captureName4; }
                else if ci == 5 { capName = stmt.child1.captureName5; }
                else if ci == 6 { capName = stmt.child1.captureName6; }
                else if ci == 7 { capName = stmt.child1.captureName7; }
                // Build: envInst.capName = capName;
                let assignNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
                assignNode.kind = hAssign;
                assignNode.line = line;
                assignNode.column = col;
                let fieldNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
                fieldNode.kind = hFieldAccess;
                fieldNode.strValue = capName;
                let baseNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
                baseNode.kind = hVar;
                baseNode.strValue = envInst;
                fieldNode.child1 = baseNode;
                let valNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
                valNode.kind = hVar;
                valNode.strValue = capName;
                assignNode.child1 = fieldNode;
                assignNode.child2 = valNode;
                if firstStmt == null as *HirNode {
                    firstStmt = assignNode;
                    lastStmt = assignNode;
                } else {
                    lastStmt.child3 = assignNode;
                    lastStmt = assignNode;
                }
                ci = ci + 1;
            }
            // Append the let store
            if firstStmt == null as *HirNode {
                firstStmt = storeNode;
                lastStmt = storeNode;
            } else {
                lastStmt.child3 = storeNode;
                lastStmt = storeNode;
            }
            // Append auto-Drop defer if present
            if deferNode != null as *HirNode {
                lastStmt.child3 = deferNode;
                lastStmt = deferNode;
            }
            blockNode.child1 = firstStmt;
            return blockNode;
        }
        // Non-closure: wrap with defer if present
        if deferNode != null as *HirNode {
            storeNode.child3 = deferNode;
            let blockNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
@@ -2244,8 +2335,16 @@ func Lcx_LowerFunc(ctx: *LowerCtx, decl: *Decl) -> *HirFunc {
    let retTe: *TypeExpr = Lcx_SubstituteType(ctx, decl.retType);
    if retTe != null as *TypeExpr {
        f.retTypeName = retTe.typeName;
        f.retTypeKind = Lcx_ResolveTypeKind(retTe);
        if retTe.kind == tekFunc {
            f.retTypeName = Lcx_BuildFuncTypeName(retTe);
        } else if !String_Eq(retTe.typeName, "") {
            f.retTypeName = retTe.typeName;
        } else if retTe.kind == tekPointer && retTe.pointerPointee != null as *TypeExpr {
            f.retTypeName = String_Concat(retTe.pointerPointee.typeName, "*");
        } else {
            f.retTypeName = "";
        }
    } else {
        f.retTypeName = "";
        f.retTypeKind = 0;
@@ -2320,25 +2419,36 @@ func Lcx_LowerClosureFunc(ctx: *LowerCtx, expr: *Expr) -> *HirFunc {
    f.isPublic = false;
    let params: *Decl = expr.closureParams;
-    if params != null as *Decl {
+    // Fat-func ABI: leading void* __env, then user params
-        f.paramCount = params.paramCount;
+    var userCount: int = 0;
-        if params.paramCount > 0 { f.param0 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param0, &params.param0, ctx); }
+    if params != null as *Decl { userCount = params.paramCount; }
-        if params.paramCount > 1 { f.param1 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param1, &params.param1, ctx); }
+    f.paramCount = userCount + 1;
-        if params.paramCount > 2 { f.param2 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param2, &params.param2, ctx); }
+    f.param0 = bux_alloc(sizeof(HirParam)) as *HirParam;
-        if params.paramCount > 3 { f.param3 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param3, &params.param3, ctx); }
+    f.param0.name = "__env";
-        if params.paramCount > 4 { f.param4 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param4, &params.param4, ctx); }
+    f.param0.typeKind = tyPointer;
-        if params.paramCount > 5 { f.param5 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param5, &params.param5, ctx); }
+    f.param0.typeName = "void*";
-        if params.paramCount > 6 { f.param6 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param6, &params.param6, ctx); }
+    if userCount > 0 { f.param1 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param1, &params.param0, ctx); }
-        if params.paramCount > 7 { f.param7 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param7, &params.param7, ctx); }
+    if userCount > 1 { f.param2 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param2, &params.param1, ctx); }
-        if params.paramCount > 8 { f.param8 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param8, &params.param8, ctx); }
+    if userCount > 2 { f.param3 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param3, &params.param2, ctx); }
-    }
+    if userCount > 3 { f.param4 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param4, &params.param3, ctx); }
    if userCount > 4 { f.param5 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param5, &params.param4, ctx); }
    if userCount > 5 { f.param6 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param6, &params.param5, ctx); }
    if userCount > 6 { f.param7 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param7, &params.param6, ctx); }
    if userCount > 7 { f.param8 = bux_alloc(sizeof(HirParam)) as *HirParam; Lcx_LowerParam(f.param8, &params.param7, ctx); }
-    if expr.refType != null as *TypeExpr && expr.refType.kind == tekFunc && expr.refType.funcRet != null as *TypeExpr {
+    if expr.refType != null as *TypeExpr && expr.refType.kind == tekFunc {
-        f.retTypeName = expr.refType.funcRet.typeName;
+        // Return type of the *thunk* is the closure's return type (not the fat type)
-        f.retTypeKind = Lcx_ResolveTypeKind(expr.refType.funcRet);
+        if expr.refType.funcRet != null as *TypeExpr {
            f.retTypeName = expr.refType.funcRet.typeName;
            if String_Eq(f.retTypeName, "") { f.retTypeName = "int"; }
            f.retTypeKind = Lcx_ResolveTypeKind(expr.refType.funcRet);
        } else {
            f.retTypeName = "void";
            f.retTypeKind = tyVoid;
        }
    } else {
-        f.retTypeName = "";
+        f.retTypeName = "int";
-        f.retTypeKind = 0;
+        f.retTypeKind = tyInt;
    }
    // Copy capture metadata from AST
@@ -277,6 +277,7 @@ func lexKeywordKind(text: String) -> int {
    if String_Eq(text, "switch") { return tkSwitch; }
    if String_Eq(text, "case") { return tkCase; }
    if String_Eq(text, "default") { return tkDefault; }
    if String_Eq(text, "unsafe") { return tkUnsafe; }
    if String_Eq(text, "async") { return tkAsync; }
    if String_Eq(text, "await") { return tkAwait; }
    if String_Eq(text, "spawn") { return tkSpawn; }
@@ -399,6 +399,15 @@ func parserParsePrimary(p: *Parser) -> *Expr {
        return parserParseClosure(p);
    }
    // unsafe { ... } — unsafe block expression
    if kind == tkUnsafe {
        discard parserAdvance(p);
        let e: *Expr = parserMakeExpr(ekBlock, line, col);
        e.boolValue = true; // marks this block as unsafe
        e.refBlock = parserParseBlock(p);
        return e;
    }
    parserEmitDiag(p, line, col, "expected expression");
    return parserMakeExpr(ekLiteral, line, col);
 }
@@ -136,7 +136,6 @@ func Sema_BuildFuncTypeExprFromDecl(decl: *Decl) -> *TypeExpr {
 func Sema_ResolveType(sema: *Sema, te: *TypeExpr) -> int {
    if te == null as *TypeExpr { return tyUnknown; }
    let name: String = te.typeName;
    if te.kind == tekPointer {
        return tyPointer;
@@ -146,33 +145,7 @@ func Sema_ResolveType(sema: *Sema, te: *TypeExpr) -> int {
        return tyFunc;
    }
-    if String_Eq(name, "void") { return tyVoid; }
+    return Type_FromName(te.typeName);
    if String_Eq(name, "bool") { return tyBool; }
    if String_Eq(name, "bool8") { return tyBool8; }
    if String_Eq(name, "bool16") { return tyBool16; }
    if String_Eq(name, "bool32") { return tyBool32; }
    if String_Eq(name, "char8") { return tyChar8; }
    if String_Eq(name, "char16") { return tyChar16; }
    if String_Eq(name, "char32") { return tyChar32; }
    if String_Eq(name, "String") { return tyStr; }
    if String_Eq(name, "str") { return tyStr; }
    if String_Eq(name, "int8") { return tyInt8; }
    if String_Eq(name, "int16") { return tyInt16; }
    if String_Eq(name, "int32") { return tyInt32; }
    if String_Eq(name, "int64") { return tyInt64; }
    if String_Eq(name, "int") { return tyInt; }
    if String_Eq(name, "uint8") { return tyUInt8; }
    if String_Eq(name, "uint16") { return tyUInt16; }
    if String_Eq(name, "uint32") { return tyUInt32; }
    if String_Eq(name, "uint64") { return tyUInt64; }
    if String_Eq(name, "uint") { return tyUInt; }
    if String_Eq(name, "float32") { return tyFloat32; }
    if String_Eq(name, "float64") { return tyFloat64; }
    if String_Eq(name, "float") { return tyFloat64; }
    // Type resolution uses scope-based lookup via Sema_CollectGlobals
    // TODO: add StringMap-based type table for faster named-type validation
    return tyNamed;
 }
 // ---------------------------------------------------------------------------
@@ -758,10 +731,17 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
        return tyUnknown;
    }
-    // Block expression
+    // Block expression (boolValue = true means unsafe block)
    if kind == ekBlock {
        if expr.refBlock != null as *Block {
-            Sema_CheckBlock(sema, expr.refBlock);
+            if expr.boolValue {
                let prevChecked: bool = sema.checkedFunc;
                sema.checkedFunc = false;
                Sema_CheckBlock(sema, expr.refBlock);
                sema.checkedFunc = prevChecked;
            } else {
                Sema_CheckBlock(sema, expr.refBlock);
            }
        }
        return tyVoid;
    }
@@ -142,6 +142,7 @@ const tkDefer: int = 106;
 const tkSwitch: int = 107;
 const tkCase: int = 108;
 const tkDefault: int = 109;
 const tkUnsafe: int = 110;
 // ---------------------------------------------------------------------------
 // Token struct
@@ -165,6 +166,7 @@ func Token_IsKeyword(kind: int) -> bool {
    if kind >= tkFunc && kind <= tkExtern { return true; }
    if kind >= tkAs && kind <= tkSuper { return true; }
    if kind == tkSizeOf { return true; }
    if kind >= tkDefer && kind <= tkUnsafe { return true; }
    if kind >= tkAsync && kind <= tkSpawn { return true; }
    return false;
 }
@@ -215,6 +217,15 @@ func Token_KeywordKind(text: String) -> int {
    if String_Eq(text, "self") { return tkSelf; }
    if String_Eq(text, "super") { return tkSuper; }
    if String_Eq(text, "sizeof") { return tkSizeOf; }
    if String_Eq(text, "defer") { return tkDefer; }
    if String_Eq(text, "switch") { return tkSwitch; }
    if String_Eq(text, "case") { return tkCase; }
    if String_Eq(text, "default") { return tkDefault; }
    if String_Eq(text, "unsafe") { return tkUnsafe; }
    if String_Eq(text, "discard") { return tkDiscard; }
    if String_Eq(text, "async") { return tkAsync; }
    if String_Eq(text, "await") { return tkAwait; }
    if String_Eq(text, "spawn") { return tkSpawn; }
    if String_Eq(text, "true") { return tkBoolLiteral; }
    if String_Eq(text, "false") { return tkBoolLiteral; }
    return tkIdent;
@@ -259,6 +270,15 @@ func Token_KindName(kind: int) -> String {
    if kind == tkNull { return "null"; }
    if kind == tkSelf { return "self"; }
    if kind == tkSuper { return "super"; }
    if kind == tkUnsafe { return "unsafe"; }
    if kind == tkDefer { return "defer"; }
    if kind == tkSwitch { return "switch"; }
    if kind == tkCase { return "case"; }
    if kind == tkDefault { return "default"; }
    if kind == tkAsync { return "async"; }
    if kind == tkAwait { return "await"; }
    if kind == tkSpawn { return "spawn"; }
    if kind == tkDiscard { return "discard"; }
    if kind == tkLParen { return "("; }
    if kind == tkRParen { return ")"; }
    if kind == tkLBrace { return "{"; }
@@ -186,4 +186,94 @@ func Type_ToString(t: Type) -> String {
    if t.kind == tyFunc { return t.name; }
    return "?";
 }
 // ---------------------------------------------------------------------------
 // Type_FromName — central type-name → kind mapping (used by sema, hir_lower)
 // ---------------------------------------------------------------------------
 func Type_FromName(name: String) -> int {
    if String_Eq(name, "void") { return tyVoid; }
    if String_Eq(name, "bool") { return tyBool; }
    if String_Eq(name, "bool8") { return tyBool8; }
    if String_Eq(name, "bool16") { return tyBool16; }
    if String_Eq(name, "bool32") { return tyBool32; }
    if String_Eq(name, "char8") { return tyChar8; }
    if String_Eq(name, "char16") { return tyChar16; }
    if String_Eq(name, "char32") { return tyChar32; }
    if String_Eq(name, "String") { return tyStr; }
    if String_Eq(name, "str") { return tyStr; }
    if String_Eq(name, "int8") { return tyInt8; }
    if String_Eq(name, "int16") { return tyInt16; }
    if String_Eq(name, "int32") { return tyInt32; }
    if String_Eq(name, "int64") { return tyInt64; }
    if String_Eq(name, "int") { return tyInt; }
    if String_Eq(name, "uint8") { return tyUInt8; }
    if String_Eq(name, "uint16") { return tyUInt16; }
    if String_Eq(name, "uint32") { return tyUInt32; }
    if String_Eq(name, "uint64") { return tyUInt64; }
    if String_Eq(name, "uint") { return tyUInt; }
    if String_Eq(name, "float32") { return tyFloat32; }
    if String_Eq(name, "float64") { return tyFloat64; }
    if String_Eq(name, "float") { return tyFloat64; }
    return tyNamed;
 }
 // ---------------------------------------------------------------------------
 // Type_ToCName — type kind → C type name (used by C backend)
 // ---------------------------------------------------------------------------
 func Type_ToCName(kind: int) -> String {
    if kind == tyVoid { return "void"; }
    if kind == tyBool || kind == tyBool8 || kind == tyBool16 || kind == tyBool32 { return "bool"; }
    if kind == tyChar8 { return "char"; }
    if kind == tyChar16 { return "uint16"; }
    if kind == tyChar32 { return "uint32"; }
    if kind == tyStr { return "String"; }
    if kind == tyInt8 { return "int8"; }
    if kind == tyInt16 { return "int16"; }
    if kind == tyInt32 { return "int32"; }
    if kind == tyInt64 { return "int64"; }
    if kind == tyInt { return "int"; }
    if kind == tyUInt8 { return "uint8"; }
    if kind == tyUInt16 { return "uint16"; }
    if kind == tyUInt32 { return "uint32"; }
    if kind == tyUInt64 { return "uint64"; }
    if kind == tyUInt { return "uint"; }
    if kind == tyFloat32 { return "float32"; }
    if kind == tyFloat64 { return "float64"; }
    if kind == tyPointer { return "void*"; }
    // Fat function pointer — concrete BuxFn_* name comes from typeName field
    if kind == tyFunc { return "BuxFn"; }
    return "";
 }
 // ---------------------------------------------------------------------------
 // Signed / Unsigned / Float predicates
 // ---------------------------------------------------------------------------
 func Type_IsSigned(kind: int) -> bool {
    return kind == tyInt8 || kind == tyInt16 || kind == tyInt32 || kind == tyInt64 || kind == tyInt;
 }
 func Type_IsUnsigned(kind: int) -> bool {
    return kind == tyUInt8 || kind == tyUInt16 || kind == tyUInt32 || kind == tyUInt64 || kind == tyUInt;
 }
 func Type_IsFloat(kind: int) -> bool {
    return kind == tyFloat32 || kind == tyFloat64;
 }
 // ---------------------------------------------------------------------------
 // Type_SizeOf — byte size of a primitive type (0 for non-primitive)
 // ---------------------------------------------------------------------------
 func Type_SizeOf(kind: int) -> int {
    if kind == tyBool || kind == tyBool8 || kind == tyChar8 || kind == tyInt8 || kind == tyUInt8 { return 1; }
    if kind == tyBool16 || kind == tyChar16 || kind == tyInt16 || kind == tyUInt16 { return 2; }
    if kind == tyBool32 || kind == tyChar32 || kind == tyInt32 || kind == tyUInt32 || kind == tyFloat32 { return 4; }
    if kind == tyInt64 || kind == tyUInt64 || kind == tyFloat64 { return 8; }
    if kind == tyInt || kind == tyUInt { return 8; }
    if kind == tyPointer { return 8; }
    return 0;
 }
 }
@@ -0,0 +1,54 @@
 #!/usr/bin/env bash
 # Golden tests for Rust-style compiler diagnostics.
 # Usage: from repo root: tests/error_golden/run.sh [path/to/buxc]
 set -euo pipefail
 ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
 BUXC="${1:-$ROOT/buxc}"
 DIR="$(cd "$(dirname "$0")" && pwd)"
 if [[ ! -x "$BUXC" ]]; then
  echo "error: buxc not found at $BUXC (run make build first)"
  exit 1
 fi
 passed=0
 failed=0
 normalize() {
  # Replace absolute path prefix with FILE, drop trailing blank lines
  sed -E \
    -e "s|$DIR/[^:]+:|FILE:|g" \
    -e "s|$ROOT/[^:]+:|FILE:|g" \
    -e "s|//+|/|g" \
    | sed -e :a -e '/^\n*$/{$d;N;ba' -e '}'
 }
 for case_dir in "$DIR"/*/; do
  name="$(basename "$case_dir")"
  [[ -f "$case_dir/expected.err" ]] || continue
  [[ -f "$case_dir/bux.toml" ]] || continue
  out="$("$BUXC" build "$case_dir" --color off 2>&1 || true)"
  got="$(printf '%s\n' "$out" | normalize)"
  exp="$(cat "$case_dir/expected.err")"
  # Compare ignoring full absolute path differences already normalized
  if [[ "$got" == "$exp" ]]; then
    echo "  PASS $name"
    passed=$((passed + 1))
  else
    echo "  FAIL $name"
    echo "---- expected ----"
    printf '%s\n' "$exp"
    echo "---- got ----"
    printf '%s\n' "$got"
    echo "--------------"
    failed=$((failed + 1))
  fi
 done
 echo "Error golden tests: $passed passed, $failed failed"
 if [[ $failed -gt 0 ]]; then
  exit 1
 fi
@@ -0,0 +1,7 @@
 [Package]
 Name    = "type_mismatch"
 Version = "0.1.0"
 Type    = "bin"
 [Build]
 Output = "Bin"
@@ -0,0 +1,7 @@
 error: type errors in project
 error: cannot assign String to int
  --> FILE:4:18
    |
 4 |     let x: int = "hello";
    |                  ^^^^^^^
   = help: ensure the right-hand side type matches the left-hand side
@@ -0,0 +1,6 @@
 import Std::Io::PrintLine;
 func Main() -> int {
    let x: int = "hello";
    return 0;
 }
@@ -0,0 +1,7 @@
 [Package]
 Name    = "undeclared"
 Version = "0.1.0"
 Type    = "bin"
 [Build]
 Output = "Bin"
@@ -0,0 +1,7 @@
 error: type errors in project
 error: undeclared identifier 'noSuchVar'
  --> FILE:4:15
    |
 4 |     PrintLine(noSuchVar);
    |               ^^^^^^^^^
   = help: check the spelling, or import the symbol from the right module
@@ -0,0 +1,6 @@
 import Std::Io::PrintLine;
 func Main() -> int {
    PrintLine(noSuchVar);
    return 0;
 }
@@ -4,7 +4,7 @@
 # Usage: bux-lsp
 # The editor spawns this binary and communicates via stdin/stdout.
-import std/[json, os, strutils, streams, tables]
+import std/[json, os, strutils, streams, tables, osproc]
 # ---------------------------------------------------------------------------
 # JSON-RPC Transport
@@ -175,19 +175,150 @@ proc analyzeFile(path: string, content: string): DocumentState =
    i += 1
 # ---------------------------------------------------------------------------
-# Diagnostics (placeholder — emits empty diagnostics)
+# Diagnostics — run `buxc check` when available and parse Rust-style errors
 # ---------------------------------------------------------------------------
-proc publishDiagnostics(stream: FileStream, uri: string) =
+type
  LspDiag = object
    line: int        ## 0-based for LSP
    col: int         ## 0-based
    endCol: int      ## 0-based exclusive
    severity: int    ## 1=error, 2=warning
    message: string
 proc findBuxc(): string =
  ## Prefer buxc next to the LSP binary, then PATH.
  let beside = getAppDir() / "buxc"
  if fileExists(beside): return beside
  let beside2 = getCurrentDir() / "buxc"
  if fileExists(beside2): return beside2
  result = findExe("buxc")
 proc parseBuxcDiagnostics(output, sourcePath: string): seq[LspDiag] =
  ## Parse lines like:
  ##   error: cannot assign String to int
  ##     --> /path/Main.bux:4:18
  result = @[]
  let lines = output.splitLines()
  var i = 0
  while i < lines.len:
    let line = lines[i]
    var sev = 0
    var msg = ""
    if line.startsWith("error: "):
      sev = 1
      msg = line[7..^1]
    elif line.startsWith("warning: "):
      sev = 2
      msg = line[9..^1]
    else:
      inc i
      continue
    # Skip aggregate headers like "type errors in project"
    if msg.startsWith("type errors") or msg.startsWith("parse errors") or
       msg.startsWith("lex errors"):
      inc i
      continue
    var fileLine = 1
    var fileCol = 1
    if i + 1 < lines.len and lines[i + 1].strip().startsWith("-->"):
      let locPart = lines[i + 1].strip()[3..^1].strip()
      # path:line:col
      let parts = locPart.rsplit(':', maxsplit = 2)
      if parts.len >= 3:
        try:
          fileLine = parseInt(parts[^2])
          fileCol = parseInt(parts[^1])
        except: discard
      # Optionally filter to the open document
      let pathPart = if parts.len >= 3: parts[0] else: ""
      if sourcePath.len > 0 and pathPart.len > 0:
        if not pathPart.endsWith(sourcePath.extractFilename) and
           pathPart != sourcePath:
          i += 1
          continue
    # Estimate end column from message quote or single caret width
    var endCol = fileCol
    let q = msg.find('\'')
    if q >= 0:
      let q2 = msg.find('\'', q + 1)
      if q2 > q + 1:
        endCol = fileCol + (q2 - q - 1)
    if endCol <= fileCol:
      endCol = fileCol + 1
    result.add(LspDiag(
      line: max(0, fileLine - 1),
      col: max(0, fileCol - 1),
      endCol: max(0, endCol - 1),
      severity: sev,
      message: msg
    ))
    inc i
 proc runBuxcDiagnostics(sourcePath, content: string): seq[LspDiag] =
  result = @[]
  let buxc = findBuxc()
  if buxc.len == 0:
    return
  # Prefer package root if this file lives under src/
  var projectDir = sourcePath.parentDir
  if projectDir.endsWith("src"):
    projectDir = projectDir.parentDir
  let toml = projectDir / "bux.toml"
  var cmd: string
  var workDir: string
  if fileExists(toml):
    workDir = projectDir
    cmd = buxc & " check --color off"
  else:
    # Temp package for free-standing buffers
    let tmp = getTempDir() / "bux-lsp-" & $getCurrentProcessId()
    createDir(tmp / "src")
    writeFile(tmp / "bux.toml", """[Package]
 Name = "lsp_tmp"
 Version = "0.0.0"
 Type = "bin"
 [Build]
 Output = "Bin"
 """)
    writeFile(tmp / "src" / "Main.bux", content)
    workDir = tmp
    cmd = buxc & " check --color off"
  try:
    let (output, _) = execCmdEx(cmd, workingDir = workDir)
    result = parseBuxcDiagnostics(output, sourcePath)
  except CatchableError:
    discard
 proc publishDiagnostics(stream: FileStream, uri: string, diags: seq[LspDiag] = @[]) =
  var arr = newJArray()
  for d in diags:
    arr.add(%*{
      "range": {
        "start": {"line": d.line, "character": d.col},
        "end": {"line": d.line, "character": d.endCol}
      },
      "severity": d.severity,
      "source": "buxc",
      "message": d.message
    })
  sendNotification(stream, "textDocument/publishDiagnostics", %*{
    "uri": uri,
-    "diagnostics": []
+    "diagnostics": arr
  })
 proc analyzeAndPublishDiagnostics(stream: FileStream, doc: DocumentState) =
-  let updated = analyzeFile(uriToPath(doc.uri), doc.content)
+  let path = uriToPath(doc.uri)
  let updated = analyzeFile(path, doc.content)
  doc.symbols = updated.symbols
-  publishDiagnostics(stream, doc.uri)
+  let diags = runBuxcDiagnostics(path, doc.content)
  publishDiagnostics(stream, doc.uri, diags)
 # ---------------------------------------------------------------------------
 # Completion