feat: pattern bindings, empty closures, match-as-expr, string interp

Sessions 10–12 from QUALITY_PLAN:

- Pattern payload bindings (Some(value) => value) in bootstrap and selfhost
- Empty-param closures via || (tkPipePipe) with loop/return bodies
- Expression-form match: let x = match …; newline before arms
- f"…" string interpolation desugared to String_Concat + conversions
- Lexer preserves \{ \} for literal braces in f-strings
- Bootstrap fix: f"plain" strips the f prefix after escape processing
- Examples: pattern_matching, closure_control, match_let, string_interp

Selfhost-loop remains binary-identical; all examples and error goldens pass.

Makefile

@@ -3,7 +3,7 @@ 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 stdlib_ergonomics tuples func_ptr map_remove array_iter_extra string_extra multi_closure iter_hof
+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 iter_hof closure_control match_let string_interp
 
 .PHONY: all build dev debug test clean clean-all test-examples selfhost test-golden test-errors selfhost-loop lsp
 

bootstrap/c_backend.nim

@@ -595,11 +595,19 @@ proc emitEnum*(be: var CBackend, name: string, variants: seq[HirEnumVariant]) =
     be.emitLine(&"typedef union {{")
     inc be.indent
     for v in variants:
-      if v.fields.len > 0:
+      if v.fields.len == 1:
-        # Positional fields
+        # Single positional field — flat union member (compat: data.Variant_0)
+        let typ = typeToC(be, v.fields[0])
+        be.emitLine(&"{typ} {v.name}_0;")
+      elif v.fields.len > 1:
+        # Multi positional fields — nested struct so fields don't overlay
+        be.emitLine(&"struct {{")
+        inc be.indent
         for i, f in v.fields:
           let typ = typeToC(be, f)
           be.emitLine(&"{typ} {v.name}_{i};")
+        dec be.indent
+        be.emitLine(&"}} {v.name};")
       elif v.namedFields.len > 0:
         # Named fields - generate as struct
         be.emitLine(&"struct {{")

bootstrap/hir_lower.nim

@@ -30,6 +30,9 @@ type
     funcAdapterSigs*: Table[string, Type]
     ## All func types that need BuxFn_* typedefs (including locals)
     seenFatTypes*: seq[Type]
+    ## Pattern-binding names already alloca'd in the current function
+    ## (avoids `int v;` twice when two matches bind the same name)
+    patternBoundNames*: HashSet[string]
 
 proc freshName(ctx: var LowerCtx): string =
   inc ctx.varCounter
@@ -73,6 +76,8 @@ proc patternLiteralNode(pat: Pattern, loc: SourceLocation): HirNode =
 proc matchAlwaysTrue(loc: SourceLocation): HirNode =
   hirLit(Token(kind: tkBoolLiteral, text: "true", loc: loc), makeBool(), loc)
 
+proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type
+
 proc matchPatternCond(ctx: var LowerCtx, subject: HirNode, pattern: Pattern,
                       subjectEnumName: string, subjectHasData: bool,
                       loc: SourceLocation): HirNode =
@@ -126,9 +131,99 @@ proc matchPatternCond(ctx: var LowerCtx, subject: HirNode, pattern: Pattern,
     # Struct/tuple patterns: not yet fully lowered — always-true
     return nil
 
+proc matchPatternBindings(ctx: var LowerCtx, subject: HirNode, pattern: Pattern,
+                          subjectEnumName: string, subjectHasData: bool,
+                          loc: SourceLocation): seq[HirNode] =
+  ## Emit alloca+store for identifiers bound by a match pattern.
+  ## Enum payload: `Option::Some(value)` → `value = subject.data.Some_0`
+  ## Ident catch-all: `x` → `x = subject`
+  result = @[]
+  if pattern == nil: return
+  case pattern.kind
+  of pkIdent:
+    let ty = if subject.typ != nil: subject.typ else: makeUnknown()
+    if pattern.patIdent notin ctx.patternBoundNames:
+      result.add(hirAlloca(pattern.patIdent, ty, loc))
+      ctx.patternBoundNames.incl(pattern.patIdent)
+    result.add(hirStore(hirVar(pattern.patIdent, ty, loc), subject, loc))
+  of pkEnum:
+    if not subjectHasData:
+      return
+    var enumName = ""
+    var variantName = ""
+    if pattern.patEnumPath.len >= 2:
+      enumName = pattern.patEnumPath[0]
+      variantName = pattern.patEnumPath[^1]
+    elif pattern.patEnumPath.len == 1:
+      variantName = pattern.patEnumPath[0]
+      enumName = subjectEnumName
+    if enumName == "" or variantName == "":
+      return
+    # Look up field types from enum declaration
+    var fieldTypes: seq[Type] = @[]
+    var namedFields: seq[tuple[name: string, typ: Type]] = @[]
+    let enumSym = ctx.globalScope.lookup(enumName)
+    if enumSym != nil and enumSym.decl != nil and enumSym.decl.kind == dkEnum:
+      for v in enumSym.decl.declEnumVariants:
+        if v.name == variantName:
+          for f in v.fields:
+            fieldTypes.add(ctx.resolveTypeExpr(f))
+          for nf in v.namedFields:
+            namedFields.add((nf.name, ctx.resolveTypeExpr(nf.ftype)))
+          break
+    let dataType = makeNamed(enumName & "_Data")
+    let dataPtr = HirNode(kind: hFieldPtr, fieldPtrBase: subject, fieldName: "data",
+                          typ: makePointer(dataType), loc: loc)
+    let dataLoad = HirNode(kind: hLoad, loadPtr: dataPtr, typ: dataType, loc: loc)
+    # Multi-field positional variants live in a nested struct data.Variant.{Variant_i}
+    # Single-field stay flat as data.Variant_0 for ABI compat.
+    let multiField = fieldTypes.len > 1
+    var payloadBase = dataLoad
+    if multiField:
+      let variantStructTy = makeNamed(variantName)
+      let variantPtr = HirNode(kind: hFieldPtr, fieldPtrBase: dataLoad, fieldName: variantName,
+                               typ: makePointer(variantStructTy), loc: loc)
+      payloadBase = HirNode(kind: hLoad, loadPtr: variantPtr, typ: variantStructTy, loc: loc)
+    for i, arg in pattern.patEnumArgs:
+      if arg == nil or arg.kind != pkIdent:
+        continue
+      let fieldName = variantName & "_" & $i
+      let fieldTy = if i < fieldTypes.len: fieldTypes[i] else: makeInt()
+      let fieldPtr = HirNode(kind: hFieldPtr, fieldPtrBase: payloadBase, fieldName: fieldName,
+                             typ: makePointer(fieldTy), loc: loc)
+      let fieldLoad = HirNode(kind: hLoad, loadPtr: fieldPtr, typ: fieldTy, loc: loc)
+      if arg.patIdent notin ctx.patternBoundNames:
+        result.add(hirAlloca(arg.patIdent, fieldTy, loc))
+        ctx.patternBoundNames.incl(arg.patIdent)
+      result.add(hirStore(hirVar(arg.patIdent, fieldTy, loc), fieldLoad, loc))
+    for nf in pattern.patEnumNamed:
+      if nf.pattern == nil or nf.pattern.kind != pkIdent:
+        continue
+      var fieldTy = makeInt()
+      for entry in namedFields:
+        if entry.name == nf.name:
+          fieldTy = entry.typ
+          break
+      # Named payload fields live under data.VariantName.name
+      let variantPtr = HirNode(kind: hFieldPtr, fieldPtrBase: dataLoad, fieldName: variantName,
+                               typ: makePointer(makeNamed(variantName)), loc: loc)
+      let variantLoad = HirNode(kind: hLoad, loadPtr: variantPtr, typ: makeNamed(variantName), loc: loc)
+      let fieldPtr = HirNode(kind: hFieldPtr, fieldPtrBase: variantLoad, fieldName: nf.name,
+                             typ: makePointer(fieldTy), loc: loc)
+      let fieldLoad = HirNode(kind: hLoad, loadPtr: fieldPtr, typ: fieldTy, loc: loc)
+      if nf.pattern.patIdent notin ctx.patternBoundNames:
+        result.add(hirAlloca(nf.pattern.patIdent, fieldTy, loc))
+        ctx.patternBoundNames.incl(nf.pattern.patIdent)
+      result.add(hirStore(hirVar(nf.pattern.patIdent, fieldTy, loc), fieldLoad, loc))
+  of pkGuarded:
+    result.add(ctx.matchPatternBindings(subject, pattern.patGuardedInner, subjectEnumName, subjectHasData, loc))
+  else:
+    discard
+
 proc lowerMatch(ctx: var LowerCtx, subject: HirNode, arms: seq[HirMatchArm], typ: Type, loc: SourceLocation): HirNode =
   ## Lower match expression to a block with if-else chain.
-  ## Supports: enum tags, integer/bool/char/string literals, ranges, wildcard/ident.
+  ## Supports: enum tags + payload bindings, integer/bool/char/string literals,
+  ## ranges, wildcard/ident catch-all.
   let hasResult = typ != nil and typ.kind != tkVoid and typ.kind != tkUnknown
   let resultName = ctx.freshName()
   var stmts: seq[HirNode] = @[]
@@ -143,8 +238,8 @@ proc lowerMatch(ctx: var LowerCtx, subject: HirNode, arms: seq[HirMatchArm], typ
     subjectEnumName = subject.typ.name
     subjectHasData = ctx.enumHasDataVariants(subjectEnumName)
 
-  proc makeArmBlock(body: HirNode): HirNode =
+  proc makeArmBlock(body: HirNode, bindStmts: seq[HirNode]): HirNode =
-    var armStmts: seq[HirNode] = @[]
+    var armStmts: seq[HirNode] = bindStmts
     if hasResult:
       armStmts.add(hirStore(hirVar(resultName, typ, loc), body, loc))
     elif body != nil:
@@ -157,7 +252,8 @@ proc lowerMatch(ctx: var LowerCtx, subject: HirNode, arms: seq[HirMatchArm], typ
 
   for i in countdown(arms.len - 1, 0):
     let arm = arms[i]
-    let armBlock = makeArmBlock(arm.body)
+    let binds = matchPatternBindings(ctx, subject, arm.pattern, subjectEnumName, subjectHasData, loc)
+    let armBlock = makeArmBlock(arm.body, binds)
     let cond = matchPatternCond(ctx, subject, arm.pattern, subjectEnumName, subjectHasData, loc)
 
     if cond == nil:
@@ -202,6 +298,7 @@ proc initLowerCtx*(module: Module, sema: Sema): LowerCtx =
   result.funcAdapters = initHashSet[string]()
   result.funcAdapterSigs = initTable[string, Type]()
   result.seenFatTypes = @[]
+  result.patternBoundNames = initHashSet[string]()
 
 proc sanitizeFatPart(s: string): string =
   result = s.replace("const char*", "cstr").replace("unsigned int", "uint")
@@ -244,8 +341,6 @@ proc hirFuncFatTypeName*(typ: Type): string =
     parts.add("void")
   return "BuxFn_" & parts.join("_")
 
-proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type
-
 proc substituteType(ctx: var LowerCtx, te: TypeExpr, subst: Table[string, Type]): Type =
   if te == nil: return makeUnknown()
   case te.kind
@@ -1314,10 +1409,51 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
 
   of ekMatch:
     let subject = ctx.lowerExpr(expr.exprMatchSubject)
+    var subjectEnumName = ""
+    var subjectHasData = false
+    if subject.typ != nil and subject.typ.kind == tkNamed:
+      subjectEnumName = subject.typ.name
+      subjectHasData = ctx.enumHasDataVariants(subjectEnumName)
+    # Prefer resolved match type; fall back to function return type when arms
+    # only reference pattern bindings (not yet in varTypeExprs during resolve).
+    var matchTyp = typ
+    if matchTyp == nil or matchTyp.kind == tkUnknown:
+      if ctx.currentFuncRetType != nil and ctx.currentFuncRetType.kind notin {tkVoid, tkUnknown}:
+        matchTyp = ctx.currentFuncRetType
     var arms: seq[HirMatchArm] = @[]
     for arm in expr.exprMatchArms:
+      # Register bind types only (do NOT call matchPatternBindings here — that
+      # would mark names as already alloca'd and lowerMatch would skip them).
+      if arm.pattern != nil and arm.pattern.kind == pkEnum and subjectHasData:
+        var enumName = ""
+        var variantName = ""
+        if arm.pattern.patEnumPath.len >= 2:
+          enumName = arm.pattern.patEnumPath[0]
+          variantName = arm.pattern.patEnumPath[^1]
+        elif arm.pattern.patEnumPath.len == 1:
+          variantName = arm.pattern.patEnumPath[0]
+          enumName = subjectEnumName
+        var fieldTypes: seq[Type] = @[]
+        let enumSym = ctx.globalScope.lookup(enumName)
+        if enumSym != nil and enumSym.decl != nil and enumSym.decl.kind == dkEnum:
+          for v in enumSym.decl.declEnumVariants:
+            if v.name == variantName:
+              for f in v.fields:
+                fieldTypes.add(ctx.resolveTypeExpr(f))
+              break
+        for i, arg in arm.pattern.patEnumArgs:
+          if arg != nil and arg.kind == pkIdent:
+            let ft = if i < fieldTypes.len: fieldTypes[i] else: makeInt()
+            ctx.varTypeExprs[arg.patIdent] = typeToTypeExpr(ft)
+      elif arm.pattern != nil and arm.pattern.kind == pkIdent:
+        let ty = if subject.typ != nil: subject.typ else: makeUnknown()
+        ctx.varTypeExprs[arm.pattern.patIdent] = typeToTypeExpr(ty)
       arms.add(HirMatchArm(pattern: arm.pattern, body: ctx.lowerExpr(arm.body)))
-    return lowerMatch(ctx, subject, arms, typ, loc)
+    # Re-resolve match type now that bindings are registered
+    if matchTyp == nil or matchTyp.kind == tkUnknown:
+      if arms.len > 0 and arms[0].body != nil and arms[0].body.typ != nil:
+        matchTyp = arms[0].body.typ
+    return lowerMatch(ctx, subject, arms, matchTyp, loc)
 
   of ekSizeOf:
     let ty = ctx.resolveTypeExpr(expr.exprSizeOfType)
@@ -1796,9 +1932,11 @@ proc lowerFunc*(ctx: var LowerCtx, decl: Decl): HirFunc =
   let oldFuncDecl = ctx.currentFuncDecl
   let oldFuncRetType = ctx.currentFuncRetType
   let oldVarTypeExprs = ctx.varTypeExprs
+  let oldPatternBound = ctx.patternBoundNames
   ctx.currentFuncRetType = retType
   ctx.currentFuncDecl = decl
   ctx.varTypeExprs = initTable[string, TypeExpr]()  # Clear local vars for new function
+  ctx.patternBoundNames = initHashSet[string]()
   # Add parameters to varTypeExprs after clearing so they are visible in the body.
   for p in funcParams:
     if p.ptype != nil:
@@ -1824,6 +1962,7 @@ proc lowerFunc*(ctx: var LowerCtx, decl: Decl): HirFunc =
   ctx.currentFuncDecl = oldFuncDecl
   ctx.currentFuncRetType = oldFuncRetType
   ctx.varTypeExprs = oldVarTypeExprs
+  ctx.patternBoundNames = oldPatternBound
 
   result = HirFunc(name: funcName, params: params, retType: retType,
                    body: body, isPublic: decl.isPublic)

bootstrap/lexer.nim

@@ -228,6 +228,9 @@ proc scanEscapeSequence(lex: var Lexer): string =
   of 'r': result = "\r"
   of 't': result = "\t"
   of '0': result = "\0"
+  of '{', '}':
+    # Preserve \{ and \} so f"..." interpolation can treat them as literal braces
+    result = "\\" & $c
   of 'x':
     var hexVal = ""
     for _ in 0..<2:

bootstrap/lir_c_backend.nim

@@ -496,9 +496,17 @@ proc emitEnumDef(be: var LirCBackend, name: string, variants: seq[HirEnumVariant
     be.emitLine(&"typedef union {{")
     be.indent += 1
     for v in variants:
-      if v.fields.len > 0:
+      if v.fields.len == 1:
+        # Single positional field — flat (compat: data.Variant_0)
+        be.emitLine(&"{typeToCStr(v.fields[0])} {v.name}_0;")
+      elif v.fields.len > 1:
+        # Multi positional — nested struct so fields don't share union storage
+        be.emitLine(&"struct {{")
+        be.indent += 1
         for i, f in v.fields:
           be.emitLine(&"{typeToCStr(f)} {v.name}_{i};")
+        be.indent -= 1
+        be.emitLine(&"}} {v.name};")
       elif v.namedFields.len > 0:
         be.emitLine(&"struct {{")
         be.indent += 1

bootstrap/parser.nim

@@ -463,7 +463,10 @@ proc parseStringInterpolation(p: var Parser, tok: Token): Expr =
     i += 1
   texts.add(currentText)
   if exprs.len == 0:
-    return newLiteralExpr(tok)
+    # f"plain" / f"use \{x\}" with no real {expr} — use processed text (escapes applied)
+    var litTok = tok
+    litTok.text = "\"" & texts[0] & "\""
+    return newLiteralExpr(litTok)
   return newStringInterpExpr(texts, exprs, tok.loc)
 
 proc parsePrimary(p: var Parser): Expr =
@@ -524,9 +527,16 @@ proc parsePrimary(p: var Parser): Expr =
     p.structInitAllowed = false
     let subject = p.parseExpr()
     p.structInitAllowed = true
+    # Same newline rules as statement-form match (needed for `let x = match ...`)
+    while p.check(tkNewLine):
+      discard p.advance()
     discard p.expect(tkLBrace, "expected '{' to start match")
     var arms: seq[MatchArm] = @[]
     while not p.check(tkRBrace) and not p.isAtEnd:
+      while p.check(tkNewLine):
+        discard p.advance()
+      if p.check(tkRBrace) or p.isAtEnd:
+        break
       let armLoc = p.currentLoc
       let pat = p.parsePattern()
       discard p.expect(tkFatArrow, "expected '=>' in match arm")
@@ -581,6 +591,17 @@ proc parsePrimary(p: var Parser): Expr =
   of tkNull:
     discard p.advance()
     return newLiteralExpr(Token(kind: tkNull, text: "null", loc: loc))
+  of tkPipePipe:
+    # Empty-param closure written as `||` — lexer merges two '|' into tkPipePipe.
+    # Disambiguate from logical-or (which only appears mid-expression): as a primary,
+    # `|| -> T { ... }` / `|| { ... }` is always a zero-param closure.
+    discard p.advance()  # ||
+    var retTypePP: TypeExpr = nil
+    if p.check(tkArrow):
+      discard p.advance()  # ->
+      retTypePP = p.parseType()
+    let bodyPP = p.parseBlock()
+    return Expr(kind: ekClosure, loc: loc, exprClosureParams: @[], exprClosureBody: bodyPP, exprClosureReturnType: retTypePP)
   of tkPipe:
     # Closure: |params| -> Ret { body }
     discard p.advance()  # |

bootstrap/sema.nim

@@ -757,26 +757,67 @@ proc checkTraitBounds(sema: var Sema, funcDecl: Decl, inferredTypes: seq[Type],
         if not sema.typeImplements(inferredTypes[i], bound):
           sema.emitError(loc, &"type '{inferredTypes[i].toString}' does not implement trait '{bound}'")
 
-proc extractPatternBindings(sema: var Sema, pat: Pattern, scope: Scope) =
+proc extractPatternBindings(sema: var Sema, pat: Pattern, scope: Scope, subjectType: Type = nil) =
-  ## Add pattern-bound identifiers to scope with unknown type (best-effort)
+  ## Add pattern-bound identifiers to scope. For enum payloads, resolve field types
+  ## from the matched enum variant so arm bodies type-check correctly.
   if pat == nil: return
   case pat.kind
   of pkIdent:
-    let sym = Symbol(kind: skVar, name: pat.patIdent, typ: makeUnknown(), isMutable: false)
+    let bindTy = if subjectType != nil and not subjectType.isUnknown: subjectType else: makeUnknown()
+    let sym = Symbol(kind: skVar, name: pat.patIdent, typ: bindTy, isMutable: false)
     discard scope.define(sym)
   of pkEnum:
-    for arg in pat.patEnumArgs:
+    # Resolve variant field types from enum declaration
-      sema.extractPatternBindings(arg, scope)
+    var enumName = ""
+    var variantName = ""
+    if pat.patEnumPath.len >= 2:
+      enumName = pat.patEnumPath[0]
+      variantName = pat.patEnumPath[^1]
+    elif pat.patEnumPath.len == 1:
+      variantName = pat.patEnumPath[0]
+      if subjectType != nil and subjectType.kind == tkNamed:
+        enumName = subjectType.name
+    var fieldTypes: seq[Type] = @[]
+    var namedFieldTypes: Table[string, Type]
+    if enumName != "":
+      let enumSym = sema.globalScope.lookup(enumName)
+      if enumSym != nil and enumSym.decl != nil and enumSym.decl.kind == dkEnum:
+        for v in enumSym.decl.declEnumVariants:
+          if v.name == variantName:
+            for f in v.fields:
+              fieldTypes.add(sema.resolveType(f))
+            for nf in v.namedFields:
+              namedFieldTypes[nf.name] = sema.resolveType(nf.ftype)
+            break
+    for i, arg in pat.patEnumArgs:
+      let argTy = if i < fieldTypes.len: fieldTypes[i] else: makeUnknown()
+      if arg.kind == pkIdent:
+        let sym = Symbol(kind: skVar, name: arg.patIdent, typ: argTy, isMutable: false)
+        discard scope.define(sym)
+      else:
+        sema.extractPatternBindings(arg, scope, argTy)
     for nf in pat.patEnumNamed:
-      sema.extractPatternBindings(nf.pattern, scope)
+      let argTy = if namedFieldTypes.hasKey(nf.name): namedFieldTypes[nf.name] else: makeUnknown()
+      if nf.pattern.kind == pkIdent:
+        let sym = Symbol(kind: skVar, name: nf.pattern.patIdent, typ: argTy, isMutable: false)
+        discard scope.define(sym)
+      else:
+        sema.extractPatternBindings(nf.pattern, scope, argTy)
   of pkTuple:
-    for elem in pat.patTupleElements:
+    for i, elem in pat.patTupleElements:
-      sema.extractPatternBindings(elem, scope)
+      let elemTy = if subjectType != nil and subjectType.kind == tkTuple and i < subjectType.inner.len:
+                     subjectType.inner[i]
+                   else: makeUnknown()
+      if elem.kind == pkIdent:
+        let sym = Symbol(kind: skVar, name: elem.patIdent, typ: elemTy, isMutable: false)
+        discard scope.define(sym)
+      else:
+        sema.extractPatternBindings(elem, scope, elemTy)
   of pkStruct:
     for f in pat.patStructFields:
       sema.extractPatternBindings(f.pattern, scope)
   of pkGuarded:
-    sema.extractPatternBindings(pat.patGuardedInner, scope)
+    sema.extractPatternBindings(pat.patGuardedInner, scope, subjectType)
   else:
     discard
 
@@ -1381,11 +1422,11 @@ proc checkExpr(sema: var Sema, expr: Expr, scope: Scope): Type =
       lastType = sema.checkStmt(stmt, blockScope)
     return lastType
   of ekMatch:
-    discard sema.checkExpr(expr.exprMatchSubject, scope)
+    let subjectType = sema.checkExpr(expr.exprMatchSubject, scope)
     var resultType = makeUnknown()
     for arm in expr.exprMatchArms:
       var armScope = newScope(scope)
-      sema.extractPatternBindings(arm.pattern, armScope)
+      sema.extractPatternBindings(arm.pattern, armScope, subjectType)
       let armType = sema.checkExpr(arm.body, armScope)
       if resultType.isUnknown:
         resultType = armType
@@ -1541,9 +1582,11 @@ proc checkStmt(sema: var Sema, stmt: Stmt, scope: Scope): Type =
     discard sema.checkStmt(Stmt(kind: skExpr, loc: stmt.stmtForBody.loc, stmtExpr: Expr(kind: ekBlock, loc: stmt.stmtForBody.loc, exprBlock: stmt.stmtForBody)), forScope)
     return makeVoid()
   of skMatch:
-    discard sema.checkExpr(stmt.stmtMatchSubject, scope)
+    let subjectType = sema.checkExpr(stmt.stmtMatchSubject, scope)
     for arm in stmt.stmtMatchArms:
-      discard sema.checkExpr(arm.body, scope)
+      var armScope = newScope(scope)
+      sema.extractPatternBindings(arm.pattern, armScope, subjectType)
+      discard sema.checkExpr(arm.body, armScope)
     return makeVoid()
   of skReturn:
     if stmt.stmtReturnValue != nil:

docs/LanguageRef.md

@@ -361,21 +361,29 @@ func Main() -> int {
 ## Pattern Matching
 
 ```bux
+// Payload bindings: names in Variant(args) are bound in the arm body
+func GetValue(opt: Option) -> int {
     match opt {
-    Option::Some(value) => PrintInt(value),
+        Option::Some(value) => value,
-    Option::None => PrintLine("none")
+        Option::None => 0
+    }
+}
+
+match n {
+    0 => 100,
+    1..5 => 200,
+    6..=10 => 300,
+    _ => -1
 }
 ```
 
 Supported patterns:
 - Wildcard: `_`
 - Literal: `42`, `"hello"`, `true`
-- Identifier: `name`
+- Identifier catch-all: `name` (binds whole subject)
 - Range: `1..9`, `1..=9`
-- Enum destructuring: `Shape::Circle(r)`
+- Enum tags + **payload bindings**: `Option::Some(value)`, `Pair::Two(a, b)`
-- Struct destructuring: `Point { x: 0, y: 0 }`
+- Struct / tuple / guard patterns: parsed; full lowering still evolving
-- Tuple: `(a, b, c)`
-- Guard: `t if t < 0`
 
 ---
 

docs/QUALITY_PLAN.md

@@ -1,7 +1,7 @@
 # Bux — План към „добър“ език (v0.5 → v1.0)
 
-> **Дата:** 2026-07-16 (вечерта)  
+> **Дата:** 2026-07-18  
-> **Текущо:** v0.5.x — selfhost loop, gradual ownership, green threads, **40+ examples**, match expr **bootstrap+selfhost** ✅  
+> **Текущо:** v0.5.x — selfhost loop, gradual ownership, green threads, **41+ examples**, match + pattern bindings + **`f"..."` interp** bootstrap+selfhost ✅  
 > **Цел:** Език, с който се пишат реални проекти комфортно, безопасно (по избор) и с надежден toolchain.
 
 ---
@@ -58,10 +58,11 @@
 | B.1 | Proper tuple types в C backend | `(T,U)` → `Tuple_T_U` struct + `.0`/`.1` | ✅ bootstrap + selfhost |
 | B.2 | Function pointer types | `func(T)->U` fat ABI | ✅ bootstrap + selfhost |
 | B.3 | Match expression lowering (literals, ranges, enums) | Expression-context match → if-else | ✅ bootstrap + selfhost |
+| B.3b | Pattern bindings (`Some(value) => value`) | Payload idents bound in arm body | ✅ bootstrap + selfhost |
 | B.4 | Closures multi-instance | Fat `BuxFn` + heap env | ✅ bootstrap + selfhost |
-| B.4b | Closures: loop/return edge cases in body | По-сложни body control-flow | ⏳ |
+| B.4b | Closures: `\|\|` empty params + loop/return body | Lexer `\|\|` vs empty closure; while/break/return | ✅ bootstrap + selfhost |
 | B.5 | По-добри diagnostics (snippet + hint) | DX #1 за нови потребители | ✅ |
-| B.6 | Bootstrap ↔ selfhost feature parity | Tuples/closures/**match** done; string interp / some ops still bootstrap-heavy | 🔄 |
+| B.6 | Bootstrap ↔ selfhost feature parity | empty `\|\|`, match-as-expr, **string interp `f"..."`** bootstrap+selfhost | ✅ |
 
 ### C — Gradual Ownership 2.0 (P1)
 
@@ -200,14 +201,44 @@ A (stdlib ergonomics)  →  B (compiler holes)  →  C (ownership depth)
 5. **Last-expr return:** `Lcx_LowerBlock` converts final `skExpr` into `return` (needed for `func F() -> T { match ... }`)
 6. Verified: `pattern_matching` via **buxc2**; simple enum + ranges; **selfhost-loop IDENTICAL ✓**
 
+## Сесия 10 (pattern bindings — B.3b)
+
+1. **Bootstrap sema:** `extractPatternBindings` resolves enum payload field types from variant decl
+2. **Bootstrap HIR:** `matchPatternBindings` → `alloca name; name = subject.data.Variant_i` before arm body
+3. **Match result type:** fall back to `currentFuncRetType` when arm bodies only use bindings
+4. **Multi-field enum layout:** positional `fields.len > 1` → nested struct in `_Data` union (no overlay)
+5. **Selfhost:** parse `patArgs` linked list; `Sema_BindPattern`; `Lcx_PatternBindings` in match arms
+6. **Example:** `pattern_matching.bux` uses `Option::Some(value) => value` (real binding, not `opt.data.Some_0`)
+7. Verified: bootstrap + **buxc2** + all examples + error goldens + **selfhost-loop IDENTICAL ✓**
+
+## Сесия 11 (empty `||` closures + match-as-expr — B.4b)
+
+1. **Bug:** `|| -> int { ... }` lexed as `tkPipePipe` (logical-or), not two `tkPipe` → empty-param closures failed to parse
+2. **Fix bootstrap:** primary `of tkPipePipe:` → zero-param `ekClosure`
+3. **Fix selfhost:** `parserParseEmptyClosure` for `tkPipePipe`
+4. **Match-as-expr:** expression-form match now skips newlines (same as statement form) → `let x = match n { ... }` works
+5. **Verified control-flow in closure body:** while/break, early return from loop, multi-return if-chain
+6. **Pattern bind reuse:** one alloca per binding name per function (`patternBoundNames`) so two matches can both use `v`
+7. **Selfhost match-as-expr:** let-init + binary operands expand yield blocks (`Lcx_IsMatchYield` / `__binop_N`)
+8. Examples: `closure_control.bux`, `match_let.bux`
+9. Verified: bootstrap + **buxc2** + all examples + error goldens + **selfhost-loop IDENTICAL ✓**
+
+## Сесия 12 (string interpolation selfhost — B.6)
+
+1. **Selfhost parser:** `parserParseStringInterp` — interleaved lit/expr parts in `callArgs`, nested fragment parse via `Lexer_Tokenize` + sub-parser
+2. **Selfhost sema/HIR:** `ekStringInterp` → `String_Concat` + `String_FromInt`/`FromBool`/`FromFloat`
+3. **Bootstrap fix:** `f"plain"` no longer keeps the `f` prefix in the literal; `\{`/`\}` preserved by lexer and unescaped by interp parser
+4. **Lexer:** `\{` / `\}` allowed (bootstrap + selfhost) so LanguageRef escape rules work
+5. **Compiler hygiene:** original dense `&&`/`||` in the large interp loop caused bootstrap OOM (~27 GB) when compiling `parser.bux` — rewrite with simpler control flow
+6. Example: `examples/string_interp.bux` (name/int/bool/plain/escaped braces)
+7. Verified: bootstrap + **buxc2** + all 41 examples + error goldens + **selfhost-loop IDENTICAL ✓**
+
 ---
 
 ## Следващи стъпки
 
 1. **LSP hover / go-to-def** (над текущите diagnostics)
 2. **Generic Iter map** (не само int), ако monomorphization с `func` params е стабилна
-3. **Closures B.4b** — loop/return edge cases in closure body
+3. Struct/tuple patterns (`Point { x, y }`, `(a, b)`) + nested bindings
-4. Struct/tuple patterns + pattern bindings (`Some(value)` binds `value`)
+4. Match arm multi-stmt bodies (beyond single expr)
-5. `let x = match ...` multi-stmt yield (beyond tail-position return)
-6. String interpolation / remaining bootstrap-only features (B.6)
 

examples/closure_control.bux

@@ -0,0 +1,63 @@
+// Closures with control flow: empty `||` params, while/break, early return
+import Std::Io::{PrintLine, PrintInt};
+import Std::Test::{Test_AssertEqInt, Test_Pass};
+
+// Zero-param capturing closure written as `||` (not `| |`)
+func MakeCounter(limit: int) -> func() -> int {
+    return || -> int {
+        var sum: int = 0;
+        var i: int = 0;
+        while i < limit {
+            sum = sum + i;
+            i = i + 1;
+            if i == 3 {
+                break;
+            }
+        }
+        return sum;
+    };
+}
+
+func MakeClamp(n: int) -> func(int) -> int {
+    return |x: int| -> int {
+        if x < 0 {
+            return 0;
+        }
+        if x > n {
+            return n;
+        }
+        return x;
+    };
+}
+
+// return from inside a loop inside a closure
+func MakeLoopReturn(n: int) -> func() -> int {
+    return || -> int {
+        var i: int = 0;
+        while i < n {
+            if i == 2 {
+                return 99;
+            }
+            i = i + 1;
+        }
+        return i;
+    };
+}
+
+func Main() -> int {
+    let c: func() -> int = MakeCounter(10);
+    Test_AssertEqInt(c(), 3); // 0+1+2
+
+    let f: func(int) -> int = MakeClamp(5);
+    Test_AssertEqInt(f(-1), 0);
+    Test_AssertEqInt(f(3), 3);
+    Test_AssertEqInt(f(100), 5);
+
+    let g: func() -> int = MakeLoopReturn(10);
+    Test_AssertEqInt(g(), 99);
+
+    PrintInt(c());
+    PrintLine("");
+    Test_Pass("closure_control");
+    return 0;
+}

examples/match_let.bux

@@ -0,0 +1,43 @@
+// Match as expression: let-init, inline arms, combined with operators
+import Std::Io::{PrintLine, PrintInt};
+import Std::Test::{Test_AssertEqInt, Test_Pass};
+
+enum Option {
+    Some(int),
+    None
+}
+
+func Main() -> int {
+    let opt: Option = Option { tag: Option_Some };
+    opt.data.Some_0 = 21;
+
+    let x: int = match opt {
+        Option::Some(v) => v + v,
+        Option::None => 0
+    };
+    Test_AssertEqInt(x, 42);
+
+    let n: int = 3;
+    let y: int = match n {
+        0 => 100,
+        1..5 => 200,
+        _ => -1
+    };
+    Test_AssertEqInt(y, 200);
+
+    let z: int = match n { 3 => 1, _ => 0 } + match n { 3 => 2, _ => 0 };
+    Test_AssertEqInt(z, 3);
+
+    let none: Option = Option { tag: Option_None };
+    // Same binding name as above — one alloca, reassigned per arm
+    let w: int = match none {
+        Option::Some(v) => v,
+        Option::None => -7
+    };
+    Test_AssertEqInt(w, -7);
+
+    PrintInt(x);
+    PrintLine("");
+    Test_Pass("match_let");
+    return 0;
+}

examples/pattern_matching.bux

@@ -1,19 +1,41 @@
-// Pattern Matching — enum tags, literals, ranges, wildcard
+// Pattern Matching — enum tags, payload bindings, literals, ranges, wildcard
 import Std::Io::{PrintLine, PrintInt};
-
+import Std::Test::{Test_AssertEqInt, Test_Pass};
 
 enum Option {
     Some(int),
     None
 }
 
+enum Msg {
+    Quit,
+    Move(int),
+    Write(String)
+}
+
 func GetValue(opt: Option) -> int {
+    // Pattern binding: value is bound from Option::Some payload
     match opt {
-        Option::Some(value) => opt.data.Some_0,
+        Option::Some(value) => value,
         Option::None => 0
     }
 }
 
+func DoubleSome(opt: Option) -> int {
+    match opt {
+        Option::Some(n) => n + n,
+        Option::None => -1
+    }
+}
+
+func MsgCode(m: Msg) -> int {
+    match m {
+        Msg::Quit => 0,
+        Msg::Move(x) => x,
+        Msg::Write(s) => 1
+    }
+}
+
 func Classify(n: int) -> int {
     // literal arms + exclusive range + inclusive range + wildcard
     match n {
@@ -40,6 +62,15 @@ func Main() -> int {
 
     let opt2: Option = Option { tag: Option_None };
 
+    Test_AssertEqInt(GetValue(opt1), 42);
+    Test_AssertEqInt(GetValue(opt2), 0);
+    Test_AssertEqInt(DoubleSome(opt1), 84);
+    Test_AssertEqInt(DoubleSome(opt2), -1);
+
+    let m: Msg = Msg { tag: Msg_Move };
+    m.data.Move_0 = 7;
+    Test_AssertEqInt(MsgCode(m), 7);
+
     PrintLine("opt1 value: ");
     PrintInt(GetValue(opt1));
     PrintLine("");
@@ -61,5 +92,6 @@ func Main() -> int {
     PrintLine("color:");
     PrintLine(ColorName(2));
 
+    Test_Pass("pattern_matching");
     return 0;
 }

examples/string_interp.bux

@@ -0,0 +1,23 @@
+import Std::Io::{PrintLine};
+import Std::Test::{Test_AssertEqString, Test_Pass};
+
+func Main() -> int {
+    let name: String = "Bux";
+    let n: int = 42;
+    let msg: String = f"Hello, {name}! count={n}";
+    PrintLine(msg);
+    Test_AssertEqString(msg, "Hello, Bux! count=42");
+
+    let flag: bool = true;
+    let bmsg: String = f"flag={flag}";
+    Test_AssertEqString(bmsg, "flag=true");
+
+    let empty: String = f"plain";
+    Test_AssertEqString(empty, "plain");
+
+    let raw: String = f"use \{braces\} literally";
+    Test_AssertEqString(raw, "use {braces} literally");
+
+    Test_Pass("string_interp");
+    return 0;
+}

src/ast.bux

@@ -79,6 +79,8 @@ struct Pattern {
     patStructName: String,   // for pkStruct
     patChild1: *Pattern,     // range lo / nested
     patChild2: *Pattern,     // range hi / nested
+    patArgs: *Pattern,       // pkEnum payload args (head)
+    patNext: *Pattern,       // next sibling in patArgs list
 }
 
 // Match arm: pattern => body

src/hir_lower.bux

@@ -533,6 +533,202 @@ func Lcx_PatternCond(ctx: *LowerCtx, subject: *HirNode, pat: *Pattern,
     return null as *HirNode;
 }
 
+// Emit binding stmts for pattern payload: Option::Some(value) → alloca value; value = subject.data.Some_0
+// Returns head of child3-linked list of HirNodes (may be null).
+func Lcx_PatternBindings(ctx: *LowerCtx, subject: *HirNode, pat: *Pattern,
+                         subjectEnumName: String, subjectHasData: bool,
+                         line: uint32, col: uint32) -> *HirNode {
+    if pat == null as *Pattern { return null as *HirNode; }
+    if pat.kind == pkIdent {
+        let ty: String = "int";
+        if subject != null as *HirNode && !String_Eq(subject.typeName, "") {
+            // keep int default for catch-all unless subject has a type name
+        }
+        let alloca: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+        alloca.kind = hAlloca;
+        alloca.line = line;
+        alloca.column = col;
+        alloca.strValue = pat.patIdent;
+        alloca.typeName = ty;
+        let store: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+        store.kind = hStore;
+        store.line = line;
+        store.column = col;
+        let v: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+        v.kind = hVar;
+        v.strValue = pat.patIdent;
+        store.child1 = v;
+        store.child2 = subject;
+        alloca.child3 = store;
+        return alloca;
+    }
+    if pat.kind != pkEnum || !subjectHasData { return null as *HirNode; }
+
+    var enumName: String = "";
+    var variantName: String = pat.patEnumPath;
+    if String_Contains(pat.patEnumPath, "::") {
+        enumName = String_SplitPart(pat.patEnumPath, "::", 0);
+        variantName = String_SplitPart(pat.patEnumPath, "::", 1);
+    } else {
+        enumName = subjectEnumName;
+    }
+    if String_Eq(enumName, "") || String_Eq(variantName, "") { return null as *HirNode; }
+
+    // Look up field type names from enum decl
+    var fieldType0: String = "int";
+    var fieldType1: String = "int";
+    var fieldCount: int = 0;
+    let enumSym: Symbol = Scope_Lookup(ctx.scope, enumName);
+    if enumSym.decl != null as *Decl && enumSym.decl.kind == dkEnum {
+        var vi: int = 0;
+        while vi < enumSym.decl.variantCount {
+            var vv: *EnumVariant = null as *EnumVariant;
+            if vi == 0 { vv = &enumSym.decl.variant0; }
+            else if vi == 1 { vv = &enumSym.decl.variant1; }
+            else if vi == 2 { vv = &enumSym.decl.variant2; }
+            else if vi == 3 { vv = &enumSym.decl.variant3; }
+            else if vi == 4 { vv = &enumSym.decl.variant4; }
+            else if vi == 5 { vv = &enumSym.decl.variant5; }
+            else if vi == 6 { vv = &enumSym.decl.variant6; }
+            else if vi == 7 { vv = &enumSym.decl.variant7; }
+            else if vi == 8 { vv = &enumSym.decl.variant8; }
+            if vv != null as *EnumVariant && String_Eq(vv.name, variantName) {
+                fieldCount = vv.fieldCount;
+                if !String_Eq(vv.fieldTypeName0, "") { fieldType0 = vv.fieldTypeName0; }
+                if !String_Eq(vv.fieldTypeName1, "") { fieldType1 = vv.fieldTypeName1; }
+            }
+            vi = vi + 1;
+        }
+    }
+
+    // dataLoad = subject.data
+    let dataPtr: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+    dataPtr.kind = hFieldPtr;
+    dataPtr.line = line;
+    dataPtr.column = col;
+    dataPtr.strValue = "data";
+    dataPtr.child1 = subject;
+    let dataLoad: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+    dataLoad.kind = hLoad;
+    dataLoad.line = line;
+    dataLoad.column = col;
+    dataLoad.child1 = dataPtr;
+    dataLoad.typeName = String_Concat(enumName, "_Data");
+
+    // Multi-field: nested struct data.Variant; single-field: flat data.Variant_0
+    var payloadBase: *HirNode = dataLoad;
+    if fieldCount > 1 {
+        let vPtr: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+        vPtr.kind = hFieldPtr;
+        vPtr.line = line;
+        vPtr.column = col;
+        vPtr.strValue = variantName;
+        vPtr.child1 = dataLoad;
+        let vLoad: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+        vLoad.kind = hLoad;
+        vLoad.line = line;
+        vLoad.column = col;
+        vLoad.child1 = vPtr;
+        vLoad.typeName = variantName;
+        payloadBase = vLoad;
+    }
+
+    var head: *HirNode = null as *HirNode;
+    var tail: *HirNode = null as *HirNode;
+    var arg: *Pattern = pat.patArgs;
+    var ai: int = 0;
+    while arg != null as *Pattern {
+        if arg.kind == pkIdent {
+            var ftype: String = "int";
+            if ai == 0 { ftype = fieldType0; }
+            else if ai == 1 { ftype = fieldType1; }
+            let fieldName: String = String_Concat(String_Concat(variantName, "_"), String_FromInt(ai as int64));
+
+            let fPtr: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            fPtr.kind = hFieldPtr;
+            fPtr.line = line;
+            fPtr.column = col;
+            fPtr.strValue = fieldName;
+            fPtr.child1 = payloadBase;
+            let fLoad: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            fLoad.kind = hLoad;
+            fLoad.line = line;
+            fLoad.column = col;
+            fLoad.child1 = fPtr;
+            fLoad.typeName = ftype;
+
+            let alloca: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            alloca.kind = hAlloca;
+            alloca.line = line;
+            alloca.column = col;
+            alloca.strValue = arg.patIdent;
+            alloca.typeName = ftype;
+
+            let store: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            store.kind = hStore;
+            store.line = line;
+            store.column = col;
+            let bv: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            bv.kind = hVar;
+            bv.strValue = arg.patIdent;
+            store.child1 = bv;
+            store.child2 = fLoad;
+            alloca.child3 = store;
+
+            // Define in scope so body idents resolve
+            var bsym: Symbol;
+            bsym.kind = skVar;
+            bsym.name = arg.patIdent;
+            bsym.typeKind = tyInt;
+            bsym.typeName = ftype;
+            bsym.refType = null as *TypeExpr;
+            bsym.isMutable = false;
+            bsym.isPublic = false;
+            bsym.decl = null as *Decl;
+            discard Scope_Define(ctx.scope, bsym);
+
+            if head == null as *HirNode {
+                head = alloca;
+                tail = store;
+            } else {
+                tail.child3 = alloca;
+                tail = store;
+            }
+        }
+        arg = arg.patNext;
+        ai = ai + 1;
+    }
+    return head;
+}
+
+// True when n is a multi-stmt yield block (match result, etc.)
+func Lcx_IsMatchYield(n: *HirNode) -> bool {
+    if n == null as *HirNode { return false; }
+    if n.kind != hBlock { return false; }
+    return !String_Eq(n.strValue, "");
+}
+
+func Lcx_YieldVarOf(n: *HirNode) -> *HirNode {
+    let v: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+    v.kind = hVar;
+    v.strValue = n.strValue;
+    v.typeName = n.typeName;
+    return v;
+}
+
+// Append `node` at the end of a child3-linked chain starting at `head` (or its child1 if head is hBlock).
+func Lcx_AppendToChain(head: *HirNode, node: *HirNode) {
+    if head == null as *HirNode || node == null as *HirNode { return; }
+    var cur: *HirNode = head;
+    if head.kind == hBlock && head.child1 != null as *HirNode {
+        cur = head.child1;
+    }
+    while cur.child3 != null as *HirNode {
+        cur = cur.child3;
+    }
+    cur.child3 = node;
+}
+
 // Lower match expr → hBlock: alloca result; if-else stores; strValue = result name
 func Lcx_LowerMatch(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
     let line: uint32 = expr.line;
@@ -591,6 +787,8 @@ func Lcx_LowerMatch(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
             continue;
         }
 
+        // Pattern bindings before body (so body idents resolve)
+        let bindHead: *HirNode = Lcx_PatternBindings(ctx, subject, cur.pattern, subjectEnumName, subjectHasData, line, col);
         let bodyHir: *HirNode = Lcx_LowerExpr(ctx, cur.body);
         // result = body
         let storeNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
@@ -603,11 +801,22 @@ func Lcx_LowerMatch(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
         storeNode.child1 = resVar;
         storeNode.child2 = bodyHir;
 
+        // armBlock = bindings... → storeNode
         let armBlock: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
         armBlock.kind = hBlock;
         armBlock.line = line;
         armBlock.column = col;
+        if bindHead != null as *HirNode {
+            armBlock.child1 = bindHead;
+            // find tail of bind chain
+            var bt: *HirNode = bindHead;
+            while bt.child3 != null as *HirNode {
+                bt = bt.child3;
+            }
+            bt.child3 = storeNode;
+        } else {
             armBlock.child1 = storeNode;
+        }
 
         let cond: *HirNode = Lcx_PatternCond(ctx, subject, cur.pattern, subjectEnumName, subjectHasData, line, col);
         if cond == null as *HirNode {
@@ -672,6 +881,72 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
         return Lcx_LowerMatch(ctx, expr);
     }
 
+    // String interpolation: desugar to String_Concat + String_FromInt/Bool/Float
+    // Parts in callArgs are interleaved text lits and expressions.
+    if kind == ekStringInterp {
+        var result: *HirNode = null as *HirNode;
+        var part: *ExprList = expr.callArgs;
+        while part != null as *ExprList {
+            let pe: *Expr = part.expr;
+            var piece: *HirNode = null as *HirNode;
+            if pe != null as *Expr && pe.kind == ekLiteral && pe.tokKind == tkStringLiteral {
+                piece = Lcx_LowerExpr(ctx, pe);
+            } else {
+                let lowered: *HirNode = Lcx_LowerExpr(ctx, pe);
+                // Convert non-string to String
+                var needConv: bool = true;
+                var convName: String = "String_FromInt";
+                if pe != null as *Expr && pe.refType != null as *TypeExpr {
+                    let tn: String = pe.refType.typeName;
+                    if String_Eq(tn, "String") || String_Eq(tn, "str") {
+                        needConv = false;
+                    } else if String_Eq(tn, "bool") {
+                        convName = "String_FromBool";
+                    } else if String_Eq(tn, "float64") || String_Eq(tn, "float") || String_Eq(tn, "float32") {
+                        convName = "String_FromFloat";
+                    } else {
+                        convName = "String_FromInt";
+                    }
+                }
+                if needConv {
+                    let callN: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+                    callN.kind = hCall;
+                    callN.line = line;
+                    callN.column = col;
+                    callN.strValue = convName;
+                    callN.child1 = lowered;
+                    piece = callN;
+                } else {
+                    piece = lowered;
+                }
+            }
+            if result == null as *HirNode {
+                result = piece;
+            } else {
+                let cat: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+                cat.kind = hCall;
+                cat.line = line;
+                cat.column = col;
+                cat.strValue = "String_Concat";
+                cat.child1 = result;
+                cat.child2 = piece;
+                result = cat;
+            }
+            part = part.next;
+        }
+        if result == null as *HirNode {
+            // empty f""
+            let empty: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            empty.kind = hLit;
+            empty.line = line;
+            empty.column = col;
+            empty.intValue = tkStringLiteral;
+            empty.strValue = "\"\"";
+            return empty;
+        }
+        return result;
+    }
+
     // Literal
     if kind == ekLiteral {
         n.kind = hLit;
@@ -874,8 +1149,69 @@ func Lcx_LowerExpr(ctx: *LowerCtx, expr: *Expr) -> *HirNode {
 
         n.kind = hBinary;
         n.intValue = expr.intValue; // operator
-        n.child1 = Lcx_LowerExpr(ctx, expr.child1);
+        let leftHir: *HirNode = Lcx_LowerExpr(ctx, expr.child1);
-        n.child2 = Lcx_LowerExpr(ctx, expr.child2);
+        let rightHir: *HirNode = Lcx_LowerExpr(ctx, expr.child2);
+        // If either side is a match yield block, expand to:
+        //   match stmts...; int __binop_N = leftVal op rightVal; yield __binop_N
+        if Lcx_IsMatchYield(leftHir) || Lcx_IsMatchYield(rightHir) {
+            ctx.varCounter = ctx.varCounter + 1;
+            let tmpName: String = String_Concat("__binop_", String_FromInt(ctx.varCounter as int64));
+            var leftVal: *HirNode = leftHir;
+            var rightVal: *HirNode = rightHir;
+            let outer: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            outer.kind = hBlock;
+            outer.line = line;
+            outer.column = col;
+            outer.strValue = tmpName;
+            outer.typeName = "int";
+            var first: *HirNode = null as *HirNode;
+            if Lcx_IsMatchYield(leftHir) {
+                leftVal = Lcx_YieldVarOf(leftHir);
+                leftHir.strValue = "";
+                first = leftHir;
+            }
+            if Lcx_IsMatchYield(rightHir) {
+                rightVal = Lcx_YieldVarOf(rightHir);
+                rightHir.strValue = "";
+                if first == null as *HirNode {
+                    first = rightHir;
+                } else {
+                    Lcx_AppendToChain(first, rightHir);
+                }
+            }
+            let tmpAlloca: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            tmpAlloca.kind = hAlloca;
+            tmpAlloca.line = line;
+            tmpAlloca.column = col;
+            tmpAlloca.strValue = tmpName;
+            tmpAlloca.typeName = "int";
+            let binNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            binNode.kind = hBinary;
+            binNode.line = line;
+            binNode.column = col;
+            binNode.intValue = expr.intValue;
+            binNode.child1 = leftVal;
+            binNode.child2 = rightVal;
+            let tmpStore: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            tmpStore.kind = hStore;
+            tmpStore.line = line;
+            tmpStore.column = col;
+            let tmpVar: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            tmpVar.kind = hVar;
+            tmpVar.strValue = tmpName;
+            tmpStore.child1 = tmpVar;
+            tmpStore.child2 = binNode;
+            tmpAlloca.child3 = tmpStore;
+            if first == null as *HirNode {
+                outer.child1 = tmpAlloca;
+            } else {
+                outer.child1 = first;
+                Lcx_AppendToChain(first, tmpAlloca);
+            }
+            return outer;
+        }
+        n.child1 = leftHir;
+        n.child2 = rightHir;
         return n;
     }
 
@@ -1875,6 +2211,26 @@ func Lcx_LowerStmt(ctx: *LowerCtx, stmt: *Stmt) -> *HirNode {
         sym.isPublic = false;
         sym.decl = null as *Decl;
         discard Scope_Define(ctx.scope, sym);
+
+        // Match (or other multi-stmt yield) as let initializer:
+        //   match stmts...; Type x = __match_N;
+        // instead of illegal `Type x = <block>;`
+        if Lcx_IsMatchYield(init) {
+            let yieldName: String = init.strValue;
+            init.strValue = "";
+            let yieldVar: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            yieldVar.kind = hVar;
+            yieldVar.strValue = yieldName;
+            let storeNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            storeNode.kind = hStore;
+            storeNode.line = line;
+            storeNode.column = col;
+            storeNode.child1 = alloca;
+            storeNode.child2 = yieldVar;
+            Lcx_AppendToChain(init, storeNode);
+            return init;
+        }
+
         // store the init value
         let storeNode: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
         storeNode.kind = hStore;
@@ -3365,11 +3721,12 @@ func HirLower_LowerModule(mod: *Module, sema: *Sema) -> *HirModule {
                     hm.enums[ei].variants[vi].name = v.name;
                     hm.enums[ei].variants[vi].fieldCount = v.fieldCount;
                     if v.fieldCount > 0 {
-                        hm.enums[ei].variants[vi].fieldName0 = "value";
+                        // Positional field names: Variant_0, Variant_1 (matches data.Variant_i / nested struct)
+                        hm.enums[ei].variants[vi].fieldName0 = String_Concat(v.name, "_0");
                         hm.enums[ei].variants[vi].fieldType0 = Lcx_ResolveTypeKindFromName(v.fieldTypeName0);
                     }
                     if v.fieldCount > 1 {
-                        hm.enums[ei].variants[vi].fieldName1 = "value2";
+                        hm.enums[ei].variants[vi].fieldName1 = String_Concat(v.name, "_1");
                         hm.enums[ei].variants[vi].fieldType1 = Lcx_ResolveTypeKindFromName(v.fieldTypeName1);
                     }
                 }

src/lexer.bux

@@ -381,8 +381,8 @@ func lexScanBacktickString(lex: *Lexer) {
     lexEmitToken(lex, tkStringLiteral);
 }
 
-func lexScanString(lex: *Lexer) {
+// Assumes lex.startPos already marked (may include f/c8/… prefix before the quote).
-    lexMarkStart(lex);
+func lexScanStringFrom(lex: *Lexer) {
     // Collect the prefix (before opening quote) for the token text
     var prefix: String = "";
     var prefixLen: int = 0;
@@ -412,6 +412,13 @@ func lexScanString(lex: *Lexer) {
             discard lexAdvance(lex);
             if !lexIsAtEnd(lex) {
                 let ec: uint32 = lexAdvance(lex);
+                // Preserve \{ and \} as two chars for f"..." brace escaping
+                if ec == 123 || ec == 125 {
+                    resolved[rpos] = 92 as char8;
+                    rpos = rpos + 1;
+                    resolved[rpos] = ec as char8;
+                    rpos = rpos + 1;
+                } else {
                     var rc: char8 = ec as char8;
                     if ec == 110 { rc = 10 as char8; }       // \n
                     else if ec == 114 { rc = 13 as char8; }  // \r
@@ -423,6 +430,7 @@ func lexScanString(lex: *Lexer) {
                     resolved[rpos] = rc;
                     rpos = rpos + 1;
                 }
+            }
         } else {
             let c: uint32 = lexAdvance(lex);
             resolved[rpos] = c as char8;
@@ -450,6 +458,11 @@ func lexScanString(lex: *Lexer) {
     lexSetLastTokenText(lex, finalBuf);
 }
 
+func lexScanString(lex: *Lexer) {
+    lexMarkStart(lex);
+    lexScanStringFrom(lex);
+}
+
 func lexScanChar(lex: *Lexer) {
     lexMarkStart(lex);
     // Collect the prefix for the token text
@@ -678,10 +691,12 @@ func lexNextToken(lex: *Lexer) {
     }
 
     // String prefixes: f" c8" c16" c32"
+    // Keep `f` in token text so the parser can detect interpolating strings.
     if c == 102 && lexPeek(lex, 1) == 34 { // f"
-        discard lexAdvance(lex); // f
+        lexMarkStart(lex);          // start at 'f'
-        lexMarkStart(lex); // treat as plain string literal in selfhost
+        discard lexAdvance(lex);    // consume f; startPos still at f
-        lexScanString(lex); return;
+        lexScanStringFrom(lex);     // does not re-mark — prefix = "f"
+        return;
     }
     if c == 99 { // 'c'
         let d: uint32 = lexPeek(lex, 1);

src/parser.bux

@@ -4,6 +4,7 @@ module Parser {
 
 extern func bux_strlen(s: String) -> uint;
 extern func bux_str_to_int(s: String) -> int64;
+extern func bux_str_slice(s: String, start: uint, len: uint) -> String;
 
 // Forward declarations for mutual recursion
 func parserParseExpr(p: *Parser) -> *Expr;
@@ -353,6 +354,171 @@ func parserMakeExpr(kind: int, line: uint32, col: uint32) -> *Expr {
     return e;
 }
 
+
+func parserMakeStringLitExpr(text: String, line: uint32, col: uint32) -> *Expr {
+    let quoted: String = String_Concat(String_Concat("\"", text), "\"");
+    let e: *Expr = parserMakeExpr(ekLiteral, line, col);
+    e.tokKind = tkStringLiteral;
+    e.tokText = quoted;
+    return e;
+}
+
+func parserParseInterpFragment(exprStr: String) -> *Expr {
+    let lex: *Lexer = Lexer_Tokenize(exprStr);
+    var sub: Parser;
+    sub.tokens = lex.tokens;
+    sub.tokenCount = lex.tokenCount;
+    sub.pos = 0;
+    sub.diagCount = 0;
+    sub.diags = null as *ParserDiag;
+    sub.structInitAllowed = true;
+    return parserParseExpr(&sub);
+}
+
+func parserAppendPart(head: *ExprList, tail: *ExprList, e: *Expr) -> *ExprList {
+    // returns new tail; head updated via pointer trick not possible — return pair as side effect on first arg using double pointer? 
+    // simpler: just inline in main
+    return tail;
+}
+
+func parserParseStringInterp(p: *Parser, tok: LexToken) -> *Expr {
+    let text: String = tok.text;
+    let tlen: uint = bux_strlen(text);
+    if tlen < 3 as uint {
+        let e: *Expr = parserMakeExpr(ekLiteral, tok.line, tok.column);
+        e.tokKind = tkStringLiteral;
+        e.tokText = text;
+        return e;
+    }
+    if text[0] as int != 102 {
+        let e: *Expr = parserMakeExpr(ekLiteral, tok.line, tok.column);
+        e.tokKind = tkStringLiteral;
+        e.tokText = text;
+        return e;
+    }
+    if text[1] as int != 34 {
+        let e: *Expr = parserMakeExpr(ekLiteral, tok.line, tok.column);
+        e.tokKind = tkStringLiteral;
+        e.tokText = text;
+        return e;
+    }
+    let inner: String = bux_str_slice(text, 2, tlen - 3);
+    let innerLen: uint = bux_strlen(inner);
+    var head: *ExprList = null as *ExprList;
+    var tail: *ExprList = null as *ExprList;
+    var currentText: String = "";
+    var i: uint = 0;
+    var partCount: int = 0;
+    while i < innerLen {
+        let ch: int = inner[i] as int;
+        var handled: bool = false;
+        if ch == 92 {
+            if i + 1 < innerLen {
+                let nch: int = inner[i + 1] as int;
+                if nch == 123 {
+                    currentText = String_Concat(currentText, "{");
+                    i = i + 2;
+                    handled = true;
+                } else {
+                    if nch == 125 {
+                        currentText = String_Concat(currentText, "}");
+                        i = i + 2;
+                        handled = true;
+                    }
+                }
+            }
+        }
+        if handled {
+            continue;
+        }
+        if ch == 123 {
+            let textPart: *Expr = parserMakeStringLitExpr(currentText, tok.line, tok.column);
+            let textNode: *ExprList = bux_alloc(sizeof(ExprList)) as *ExprList;
+            textNode.expr = textPart;
+            textNode.next = null as *ExprList;
+            textNode.argName = "";
+            if head == null as *ExprList {
+                head = textNode;
+                tail = textNode;
+            } else {
+                tail.next = textNode;
+                tail = textNode;
+            }
+            partCount = partCount + 1;
+            currentText = "";
+            var j: uint = i + 1;
+            var depth: int = 1;
+            while j < innerLen {
+                if depth <= 0 {
+                    break;
+                }
+                let cj: int = inner[j] as int;
+                if cj == 123 {
+                    depth = depth + 1;
+                }
+                if cj == 125 {
+                    depth = depth - 1;
+                }
+                j = j + 1;
+            }
+            if depth != 0 {
+                parserEmitDiag(p, tok.line, tok.column, "unmatched brace in string interpolation");
+                let bad: *Expr = parserMakeExpr(ekLiteral, tok.line, tok.column);
+                bad.tokKind = tkStringLiteral;
+                bad.tokText = "\"\"";
+                return bad;
+            }
+            let exprLen: uint = j - i - 2;
+            let exprStr: String = bux_str_slice(inner, i + 1, exprLen);
+            if bux_strlen(exprStr) == 0 {
+                parserEmitDiag(p, tok.line, tok.column, "empty interpolation");
+                let bad: *Expr = parserMakeExpr(ekLiteral, tok.line, tok.column);
+                bad.tokKind = tkStringLiteral;
+                bad.tokText = "\"\"";
+                return bad;
+            }
+            let frag: *Expr = parserParseInterpFragment(exprStr);
+            let fragNode: *ExprList = bux_alloc(sizeof(ExprList)) as *ExprList;
+            fragNode.expr = frag;
+            fragNode.next = null as *ExprList;
+            fragNode.argName = "";
+            if head == null as *ExprList {
+                head = fragNode;
+                tail = fragNode;
+            } else {
+                tail.next = fragNode;
+                tail = fragNode;
+            }
+            partCount = partCount + 1;
+            i = j;
+            continue;
+        }
+        let one: String = bux_str_slice(inner, i, 1);
+        currentText = String_Concat(currentText, one);
+        i = i + 1;
+    }
+    let lastPart: *Expr = parserMakeStringLitExpr(currentText, tok.line, tok.column);
+    let lastNode: *ExprList = bux_alloc(sizeof(ExprList)) as *ExprList;
+    lastNode.expr = lastPart;
+    lastNode.next = null as *ExprList;
+    lastNode.argName = "";
+    if head == null as *ExprList {
+        head = lastNode;
+        tail = lastNode;
+    } else {
+        tail.next = lastNode;
+        tail = lastNode;
+    }
+    partCount = partCount + 1;
+    if partCount == 1 {
+        return head.expr;
+    }
+    let e: *Expr = parserMakeExpr(ekStringInterp, tok.line, tok.column);
+    e.callArgs = head;
+    e.callArgCount = partCount;
+    return e;
+}
+
 // ---------------------------------------------------------------------------
 // Primary expressions
 // ---------------------------------------------------------------------------
@@ -370,6 +536,10 @@ func parserParsePrimary(p: *Parser) -> *Expr {
     if kind == tkIntLiteral || kind == tkFloatLiteral || kind == tkStringLiteral
         || kind == tkCharLiteral || kind == tkBoolLiteral {
         discard parserAdvance(p);
+        if kind == tkStringLiteral && bux_strlen(tok.text) >= 2 as uint
+            && tok.text[0] as int == 102 && tok.text[1] as int == 34 {
+            return parserParseStringInterp(p, tok);
+        }
         let e: *Expr = parserMakeExpr(ekLiteral, line, col);
         e.tokKind = kind;
         e.tokText = tok.text;
@@ -480,6 +650,12 @@ func parserParsePrimary(p: *Parser) -> *Expr {
         return first;
     }
 
+    // Empty-param closure: `||` is lexed as tkPipePipe (logical-or token).
+    // As a primary it can only mean a zero-param closure: || -> T { ... }
+    if kind == tkPipePipe {
+        return parserParseEmptyClosure(p);
+    }
+
     // Closure: |params| -> Ret { body }
     if kind == tkPipe {
         return parserParseClosure(p);
@@ -520,6 +696,8 @@ func parserMakePattern(kind: int, line: uint32, col: uint32) -> *Pattern {
     pat.patStructName = "";
     pat.patChild1 = null as *Pattern;
     pat.patChild2 = null as *Pattern;
+    pat.patArgs = null as *Pattern;
+    pat.patNext = null as *Pattern;
     return pat;
 }
 
@@ -565,11 +743,20 @@ func parserParsePrimaryPattern(p: *Parser) -> *Pattern {
                 path = String_Concat(path, "::");
                 path = String_Concat(path, seg.text);
             }
-            // Optional (args) for algebraic variants — parse and ignore bindings for now
+            // Optional (args) for algebraic variants — store as patArgs linked list
+            var enumArgs: *Pattern = null as *Pattern;
+            var lastArg: *Pattern = null as *Pattern;
             if parserCheck(p, tkLParen) {
                 discard parserAdvance(p);
                 while !parserCheck(p, tkRParen) && parserPeek(p, 0) != tkEndOfFile {
-                    discard parserParsePattern(p);
+                    let argPat: *Pattern = parserParsePattern(p);
+                    if enumArgs == null as *Pattern {
+                        enumArgs = argPat;
+                        lastArg = argPat;
+                    } else {
+                        lastArg.patNext = argPat;
+                        lastArg = argPat;
+                    }
                     if parserCheck(p, tkComma) { discard parserAdvance(p); }
                     else { break; }
                 }
@@ -577,19 +764,30 @@ func parserParsePrimaryPattern(p: *Parser) -> *Pattern {
             }
             let pat: *Pattern = parserMakePattern(pkEnum, line, col);
             pat.patEnumPath = path;
+            pat.patArgs = enumArgs;
             return pat;
         }
         // Bare name with (args): Variant(...) treated as single-segment enum
         if parserCheck(p, tkLParen) {
             discard parserAdvance(p);
+            var bareArgs: *Pattern = null as *Pattern;
+            var bareLast: *Pattern = null as *Pattern;
             while !parserCheck(p, tkRParen) && parserPeek(p, 0) != tkEndOfFile {
-                discard parserParsePattern(p);
+                let argPat: *Pattern = parserParsePattern(p);
+                if bareArgs == null as *Pattern {
+                    bareArgs = argPat;
+                    bareLast = argPat;
+                } else {
+                    bareLast.patNext = argPat;
+                    bareLast = argPat;
+                }
                 if parserCheck(p, tkComma) { discard parserAdvance(p); }
                 else { break; }
             }
             discard parserExpect(p, tkRParen, "expected ')' to close pattern");
             let pat: *Pattern = parserMakePattern(pkEnum, line, col);
             pat.patEnumPath = name;
+            pat.patArgs = bareArgs;
             return pat;
         }
         // Ident binding / catch-all name
@@ -629,6 +827,8 @@ func parserParseMatchExpr(p: *Parser) -> *Expr {
     p.structInitAllowed = false;
     let subject: *Expr = parserParseExpr(p);
     p.structInitAllowed = true;
+    // Allow newline before '{' (needed for `let x = match n \n { ... }`)
+    while parserCheck(p, tkNewLine) { discard parserAdvance(p); }
     discard parserExpect(p, tkLBrace, "expected '{' to start match body");
 
     var firstArm: *MatchArm = null as *MatchArm;
@@ -674,6 +874,24 @@ func parserParseMatchExpr(p: *Parser) -> *Expr {
 // Closure: |params| -> Ret { body }
 // ---------------------------------------------------------------------------
 
+// Zero-param closure when written as `||` (single tkPipePipe token from lexer)
+func parserParseEmptyClosure(p: *Parser) -> *Expr {
+    let line: uint32 = parserCurToken(p).line;
+    let col: uint32 = parserCurToken(p).column;
+    discard parserAdvance(p); // ||
+    let e: *Expr = parserMakeExpr(ekClosure, line, col);
+    let params: *Decl = bux_alloc(sizeof(Decl)) as *Decl;
+    params.kind = dkFunc;
+    params.paramCount = 0;
+    e.closureParams = params;
+    if parserCheck(p, tkArrow) {
+        discard parserAdvance(p);
+        e.refType = parserParseType(p);
+    }
+    e.refBlock = parserParseBlock(p);
+    return e;
+}
+
 func parserParseClosure(p: *Parser) -> *Expr {
     let line: uint32 = parserCurToken(p).line;
     let col: uint32 = parserCurToken(p).column;

src/sema.bux

@@ -384,6 +384,97 @@ func Sema_AddCapture(closureExpr: *Expr, name: String, typeKind: int) {
 // Expression type checking
 // ---------------------------------------------------------------------------
 
+// Bind identifiers from a match pattern into the current scope.
+// Enum payloads: Option::Some(value) → value:int (from variant field type).
+func Sema_BindPattern(sema: *Sema, pat: *Pattern, subject: *Expr) {
+    if pat == null as *Pattern { return; }
+    if pat.kind == pkIdent {
+        var sym: Symbol;
+        Sema_ZeroInitSymbol(&sym);
+        sym.kind = skVar;
+        sym.name = pat.patIdent;
+        sym.typeKind = tyInt;
+        sym.typeName = "int";
+        if subject != null as *Expr && subject.refType != null as *TypeExpr {
+            sym.refType = subject.refType;
+            sym.typeName = subject.refType.typeName;
+            sym.typeKind = Sema_ResolveType(sema, subject.refType);
+        }
+        sym.isMutable = false;
+        sym.isPublic = false;
+        sym.decl = null as *Decl;
+        discard Scope_Define(sema.scope, sym);
+        return;
+    }
+    if pat.kind == pkEnum {
+        // Resolve enum + variant field types for payload bindings
+        var enumName: String = "";
+        var variantName: String = pat.patEnumPath;
+        if String_Contains(pat.patEnumPath, "::") {
+            enumName = String_SplitPart(pat.patEnumPath, "::", 0);
+            variantName = String_SplitPart(pat.patEnumPath, "::", 1);
+        } else if subject != null as *Expr && subject.refType != null as *TypeExpr {
+            enumName = subject.refType.typeName;
+        }
+        var fieldType0: String = "int";
+        var fieldType1: String = "int";
+        var fieldCount: int = 0;
+        if !String_Eq(enumName, "") {
+            let enumSym: Symbol = Scope_Lookup(sema.scope, enumName);
+            if enumSym.decl != null as *Decl && enumSym.decl.kind == dkEnum {
+                var vi: int = 0;
+                while vi < enumSym.decl.variantCount {
+                    var v: *EnumVariant = null as *EnumVariant;
+                    if vi == 0 { v = &enumSym.decl.variant0; }
+                    else if vi == 1 { v = &enumSym.decl.variant1; }
+                    else if vi == 2 { v = &enumSym.decl.variant2; }
+                    else if vi == 3 { v = &enumSym.decl.variant3; }
+                    else if vi == 4 { v = &enumSym.decl.variant4; }
+                    else if vi == 5 { v = &enumSym.decl.variant5; }
+                    else if vi == 6 { v = &enumSym.decl.variant6; }
+                    else if vi == 7 { v = &enumSym.decl.variant7; }
+                    else if vi == 8 { v = &enumSym.decl.variant8; }
+                    if v != null as *EnumVariant && String_Eq(v.name, variantName) {
+                        fieldCount = v.fieldCount;
+                        if !String_Eq(v.fieldTypeName0, "") { fieldType0 = v.fieldTypeName0; }
+                        if !String_Eq(v.fieldTypeName1, "") { fieldType1 = v.fieldTypeName1; }
+                    }
+                    vi = vi + 1;
+                }
+            }
+        }
+        var arg: *Pattern = pat.patArgs;
+        var ai: int = 0;
+        while arg != null as *Pattern {
+            if arg.kind == pkIdent {
+                var ftype: String = "int";
+                if ai == 0 { ftype = fieldType0; }
+                else if ai == 1 { ftype = fieldType1; }
+                var bsym: Symbol;
+                Sema_ZeroInitSymbol(&bsym);
+                bsym.kind = skVar;
+                bsym.name = arg.patIdent;
+                bsym.typeName = ftype;
+                bsym.typeKind = tyInt;
+                if String_Eq(ftype, "String") || String_Eq(ftype, "str") { bsym.typeKind = tyStr; }
+                else if String_Eq(ftype, "bool") { bsym.typeKind = tyBool; }
+                else if String_Eq(ftype, "float64") || String_Eq(ftype, "float") { bsym.typeKind = tyFloat64; }
+                let te: *TypeExpr = bux_alloc(sizeof(TypeExpr)) as *TypeExpr;
+                te.kind = tekNamed;
+                te.typeName = ftype;
+                bsym.refType = te;
+                bsym.isMutable = false;
+                bsym.isPublic = false;
+                bsym.decl = null as *Decl;
+                discard Scope_Define(sema.scope, bsym);
+            }
+            arg = arg.patNext;
+            ai = ai + 1;
+        }
+        return;
+    }
+}
+
 func Sema_IsMutRefDeref(target: *Expr) -> bool {
     if target == null as *Expr { return false; }
     if target.kind != ekUnary { return false; }
@@ -790,7 +881,13 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
         var first: bool = true;
         var arm: *MatchArm = expr.matchArms;
         while arm != null as *MatchArm {
+            // Pattern bindings: Option::Some(value) → define value in arm scope
+            let armScope: Scope = Scope_NewChild(sema.scope);
+            let savedScope: *Scope = sema.scope;
+            sema.scope = &armScope;
+            Sema_BindPattern(sema, arm.pattern, expr.child1);
             let bt: int = Sema_CheckExpr(sema, arm.body);
+            sema.scope = savedScope;
             if first {
                 armType = bt;
                 first = false;
@@ -823,6 +920,20 @@ func Sema_CheckExpr(sema: *Sema, expr: *Expr) -> int {
         return armType;
     }
 
+    // String interpolation f"...{expr}..." → String
+    if kind == ekStringInterp {
+        var part: *ExprList = expr.callArgs;
+        while part != null as *ExprList {
+            discard Sema_CheckExpr(sema, part.expr);
+            part = part.next;
+        }
+        let te: *TypeExpr = bux_alloc(sizeof(TypeExpr)) as *TypeExpr;
+        te.kind = tekNamed;
+        te.typeName = "String";
+        expr.refType = te;
+        return tyStr;
+    }
+
     // Closure: |params| -> Ret { body }
     if kind == ekClosure {
         let savedRetType: int = sema.currentRetType;