feat: generic enums, fix is-operator, Type_Eq, hardcoded limit diagnostics

- feat: generic enum support (parser, lowering, codegen — both selfhost + bootstrap)
  - enum Result<T,E> { Ok(T), Err(E) } parsing + monomorphization
  - tag constant mangling in monomorphized function bodies
  - data field access (l-value + r-value) for generated enum instances
  - multiple concrete instances in same file
  - HIR walker for enum reference mangling (selfhost + bootstrap)

- feat: stdlib Result<T,E> and Option<T> made truly generic
  - breaking: explicit type args required (Result<int, String>)

- fix: 'is' operator — lowering to hBinary tag comparison + C backend fallback
- fix: Type_Eq structural comparison (inner types for pointer/slice/tuple)
- fix: hardcoded limit diagnostics (>8 params/variants/captures now emit errors)
- docs: Iter<T> safety warning for dangling pointer
- docs: IMPROVEMENTS.md — comprehensive plan and changelog
- test: generic_enum example added to EXAMPLES

All tests pass (0 FAIL). Selfhost loop deterministic.

Makefile

@@ -5,7 +5,7 @@ BUILD_DIR := build
 # Project-local nimcache so CI can cache compiles (default is ~/.cache/nim).
 NIMFLAGS ?= --nimcache:nimcache
 
-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 ownership_checked ownership_release drop_early_return lifetime_elision ctfe ctfe_crc 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 iter_generic generic_infer_hof struct_tuple_pat match_block nested_patterns match_guards pattern_shadow move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw macro_type collections_extra
+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 ownership_checked ownership_release drop_early_return lifetime_elision ctfe ctfe_crc 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 iter_generic generic_infer_hof struct_tuple_pat match_block nested_patterns match_guards pattern_shadow move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw macro_type collections_extra generic_enum
 
 # Platform smoke (macOS CI): full EXAMPLES still runs on Linux.
 EXAMPLES_SMOKE := hello ownership ownership_release strings map move_field move_field_partial move_field_remaining move_field_nested move_field_ptr move_cross_fn c_precedence macro_twice macro_repeat macro_nested macro_hygiene macro_unhygienic macro_stmt_pat macro_tt macro_tt_raw ctfe_crc

bootstrap/ast.nim

@@ -462,6 +462,7 @@ type
     of dkEnum:
       declEnumName*: string
       declEnumBaseType*: TypeExpr
+      declEnumTypeParams*: seq[TypeParam]
       declEnumVariants*: seq[EnumVariant]
     of dkUnion:
       declUnionName*: string

bootstrap/hir_lower.nim

@@ -18,6 +18,9 @@ type
     generatedStructInsts*: Table[string, bool]  # Track generated struct instantiations
     extraStructs*: seq[tuple[name: string, fields: seq[tuple[name: string, typ: Type]]]]
     structInstMap*: Table[string, tuple[baseName: string, typeArgs: seq[Type]]]  # Mangled name -> base + args
+    genericEnums*: Table[string, Decl]  # Generic enum declarations
+    generatedEnumInsts*: Table[string, bool]  # Track generated enum instantiations
+    extraEnums*: seq[tuple[name: string, variants: seq[HirEnumVariant]]]
     genericFuncs*: Table[string, Decl]  # Generic function declarations
     generatedFuncInsts*: Table[string, bool]  # Track generated function instantiations
     extraFuncs*: seq[HirFunc]  # Monomorphized generic methods
@@ -38,6 +41,8 @@ type
     ## Locals whose value was moved into another owner (struct field, let, return).
     ## Auto-Drop is skipped for these (session 37 — field-move ownership).
     movedOutLocals*: HashSet[string]
+    ## Current let/var init type (for inferring generic enum concrete names in struct inits)
+    currentInitTypeExpr*: TypeExpr
     ## Partial field moves: local → dotted paths moved out by value
     ## (e.g. "items", "inner.items" for nested `a.b.c` — session 70/73).
     ## When parent Type_Drop is skipped, remaining droppable fields still Drop.
@@ -876,6 +881,9 @@ proc initLowerCtx*(module: Module, sema: Sema): LowerCtx =
   result.generatedStructInsts = initTable[string, bool]()
   result.extraStructs = @[]
   result.structInstMap = initTable[string, tuple[baseName: string, typeArgs: seq[Type]]]()
+  result.genericEnums = initTable[string, Decl]()
+  result.generatedEnumInsts = initTable[string, bool]()
+  result.extraEnums = @[]
   result.genericFuncs = initTable[string, Decl]()
   result.generatedFuncInsts = initTable[string, bool]()
   result.extraFuncs = @[]
@@ -970,6 +978,56 @@ proc substituteType(ctx: var LowerCtx, te: TypeExpr, subst: Table[string, Type])
           ctx.generatedStructInsts[mangledName] = true
           ctx.structInstMap[mangledName] = (te.typeName, concreteArgs)
       return makeNamed(mangledName)
+    if te.typeArgs.len > 0 and ctx.genericEnums.hasKey(te.typeName):
+      var suffix = ""
+      for i, arg in te.typeArgs:
+        if i > 0: suffix.add("_")
+        let argType = substituteType(ctx, arg, subst)
+        suffix.add(argType.toString)
+      let mangledName = te.typeName & "_" & suffix
+      if not ctx.generatedEnumInsts.hasKey(mangledName):
+        let genericDecl = ctx.genericEnums[te.typeName]
+        var hasUnresolved = false
+        for arg in te.typeArgs:
+          let argType = substituteType(ctx, arg, subst)
+          for tp in genericDecl.declEnumTypeParams:
+            if argType.kind == tkNamed and argType.name == tp.name:
+              hasUnresolved = true
+              break
+          if hasUnresolved: break
+        if not hasUnresolved:
+          var localSubst = subst
+          for j, tp in genericDecl.declEnumTypeParams:
+            if j < te.typeArgs.len:
+              localSubst[tp.name] = substituteType(ctx, te.typeArgs[j], subst)
+          var variants: seq[HirEnumVariant] = @[]
+          for v in genericDecl.declEnumVariants:
+            var fields: seq[Type] = @[]
+            for f in v.fields:
+              fields.add(if f != nil: substituteType(ctx, f, localSubst) else: makeUnknown())
+            var namedFields: seq[tuple[name: string, typ: Type]] = @[]
+            for nf in v.namedFields:
+              let fType = if nf.ftype != nil: substituteType(ctx, nf.ftype, localSubst) else: makeUnknown()
+              namedFields.add((nf.name, fType))
+            variants.add(HirEnumVariant(name: v.name, fields: fields, namedFields: namedFields))
+            if fields.len > 1:
+              var nestedFields: seq[tuple[name: string, typ: Type]] = @[]
+              for i, ft in fields:
+                nestedFields.add((v.name & "_" & $i, ft))
+              let nestedName = mangledName & "_" & v.name & "_Payload"
+              ctx.extraStructs.add((nestedName, nestedFields))
+            elif namedFields.len > 0:
+              var nestedFields: seq[tuple[name: string, typ: Type]] = @[]
+              for nf in namedFields:
+                nestedFields.add((nf.name, nf.typ))
+              let nestedName = mangledName & "_" & v.name & "_Payload"
+              ctx.extraStructs.add((nestedName, nestedFields))
+          ctx.extraEnums.add((mangledName, variants))
+          ctx.generatedEnumInsts[mangledName] = true
+          var concreteArgs: seq[Type] = @[]
+          for arg in te.typeArgs: concreteArgs.add(ctx.resolveTypeExpr(arg))
+          ctx.structInstMap[mangledName] = (te.typeName, concreteArgs)
+      return makeNamed(mangledName)
     return ctx.resolveTypeExpr(te)
   of tekOwn:
     return substituteType(ctx, te.pointerPointee, subst)
@@ -1029,6 +1087,56 @@ proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type =
           ctx.generatedStructInsts[mangledName] = true
           ctx.structInstMap[mangledName] = (te.typeName, concreteArgs)
       return makeNamed(mangledName)
+    if te.typeArgs.len > 0 and ctx.genericEnums.hasKey(te.typeName):
+      var suffix = ""
+      for i, arg in te.typeArgs:
+        if i > 0: suffix.add("_")
+        let argType = ctx.resolveTypeExpr(arg)
+        suffix.add(argType.toString)
+      let mangledName = te.typeName & "_" & suffix
+      if not ctx.generatedEnumInsts.hasKey(mangledName):
+        let genericDecl = ctx.genericEnums[te.typeName]
+        var hasUnresolved = false
+        for arg in te.typeArgs:
+          let argType = ctx.resolveTypeExpr(arg)
+          for tp in genericDecl.declEnumTypeParams:
+            if argType.kind == tkNamed and argType.name == tp.name:
+              hasUnresolved = true
+              break
+          if hasUnresolved: break
+        if not hasUnresolved:
+          var subst = initTable[string, Type]()
+          for j, tp in genericDecl.declEnumTypeParams:
+            if j < te.typeArgs.len:
+              subst[tp.name] = ctx.resolveTypeExpr(te.typeArgs[j])
+          var variants: seq[HirEnumVariant] = @[]
+          for v in genericDecl.declEnumVariants:
+            var fields: seq[Type] = @[]
+            for f in v.fields:
+              fields.add(if f != nil: substituteType(ctx, f, subst) else: makeUnknown())
+            var namedFields: seq[tuple[name: string, typ: Type]] = @[]
+            for nf in v.namedFields:
+              let fType = if nf.ftype != nil: substituteType(ctx, nf.ftype, subst) else: makeUnknown()
+              namedFields.add((nf.name, fType))
+            variants.add(HirEnumVariant(name: v.name, fields: fields, namedFields: namedFields))
+            if fields.len > 1:
+              var nestedFields: seq[tuple[name: string, typ: Type]] = @[]
+              for i, ft in fields:
+                nestedFields.add((v.name & "_" & $i, ft))
+              let nestedName = mangledName & "_" & v.name & "_Payload"
+              ctx.extraStructs.add((nestedName, nestedFields))
+            elif namedFields.len > 0:
+              var nestedFields: seq[tuple[name: string, typ: Type]] = @[]
+              for nf in namedFields:
+                nestedFields.add((nf.name, nf.typ))
+              let nestedName = mangledName & "_" & v.name & "_Payload"
+              ctx.extraStructs.add((nestedName, nestedFields))
+          ctx.extraEnums.add((mangledName, variants))
+          ctx.generatedEnumInsts[mangledName] = true
+          var concreteArgs2: seq[Type] = @[]
+          for arg in te.typeArgs: concreteArgs2.add(ctx.resolveTypeExpr(arg))
+          ctx.structInstMap[mangledName] = (te.typeName, concreteArgs2)
+      return makeNamed(mangledName)
     case te.typeName
     of "void": return makeVoid()
     of "bool": return makeBool()
@@ -1171,23 +1279,39 @@ proc resolveExprType(ctx: var LowerCtx, expr: Expr): Type =
       # Check if this is a _Data union field access
       if objType.name.endsWith("_Data"):
         let enumName = objType.name[0..^6]
-        let enumSym = ctx.globalScope.lookup(enumName)
+        var enumSym = ctx.globalScope.lookup(enumName)
+        var enumDecl: Decl = nil
         if enumSym != nil and enumSym.decl != nil and enumSym.decl.kind == dkEnum:
-          for variant in enumSym.decl.declEnumVariants:
+          enumDecl = enumSym.decl
+        elif ctx.structInstMap.hasKey(enumName):
+          let (baseName, typeArgs) = ctx.structInstMap[enumName]
+          let baseSym = ctx.globalScope.lookup(baseName)
+          if baseSym != nil and baseSym.decl != nil and baseSym.decl.kind == dkEnum:
+            enumDecl = baseSym.decl
+        if enumDecl != nil:
+          var subst = initTable[string, Type]()
+          if ctx.structInstMap.hasKey(enumName):
+            var ti: int = 0
+            for tp in enumDecl.declEnumTypeParams:
+              if ti < ctx.structInstMap[enumName][1].len:
+                subst[tp.name] = ctx.structInstMap[enumName][1][ti]
+              ti = ti + 1
+          for variant in enumDecl.declEnumVariants:
             for i, f in variant.fields:
               let fieldName = variant.name & "_" & $i
               if fieldName == expr.exprFieldName:
-                return ctx.resolveTypeExpr(f)
+                return substituteType(ctx, f, subst)
             for nf in variant.namedFields:
               if nf.name == expr.exprFieldName:
-                return ctx.resolveTypeExpr(nf.ftype)
+                return substituteType(ctx, nf.ftype, subst)
       var sym = ctx.globalScope.lookup(objType.name)
       var decl = if sym != nil: sym.decl else: nil
       # If the type is a monomorphized generic struct instance, look up the base
       if decl == nil and ctx.structInstMap.hasKey(objType.name):
         let (baseName, typeArgs) = ctx.structInstMap[objType.name]
         let baseSym = ctx.globalScope.lookup(baseName)
-        if baseSym != nil and baseSym.decl != nil and baseSym.decl.kind == dkStruct:
+        if baseSym != nil and baseSym.decl != nil:
+          if baseSym.decl.kind == dkStruct:
             decl = baseSym.decl
             var subst = initTable[string, Type]()
             for i, tp in decl.declStructTypeParams:
@@ -1212,6 +1336,12 @@ proc resolveExprType(ctx: var LowerCtx, expr: Expr): Type =
                   of tekOwn, tekPointer:
                     return substituteType(ctx, f.ftype, subst)
                   else: return makeUnknown()
+          elif baseSym.decl.kind == dkEnum:
+            # Generated enum struct: fields are tag and data
+            if expr.exprFieldName == "tag":
+              return makeNamed(objType.name & "_Tag")
+            if expr.exprFieldName == "data":
+              return makeNamed(objType.name & "_Data")
       if decl != nil:
         case decl.kind
         of dkStruct:
@@ -1849,6 +1979,16 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
         let argType = ctx.resolveTypeExpr(targ)
         suffix.add(argType.toString)
       structName = structName & "_" & suffix
+    elif ctx.currentInitTypeExpr != nil and ctx.currentInitTypeExpr.kind == tekNamed and
+         ctx.currentInitTypeExpr.typeName == structName and
+         ctx.currentInitTypeExpr.typeArgs.len > 0:
+      # Infer type args from enclosing let/var declaration
+      var suffix = ""
+      for i, targ in ctx.currentInitTypeExpr.typeArgs:
+        if i > 0: suffix.add("_")
+        let argType = ctx.resolveTypeExpr(targ)
+        suffix.add(argType.toString)
+      structName = structName & "_" & suffix
     # Simple enum init: EnumName { tag: EnumName_Variant } -> EnumName_Variant
     var enumDecl: Decl = nil
     let enumSym = ctx.globalScope.lookup(structName)
@@ -2181,7 +2321,9 @@ proc lowerStmt(ctx: var LowerCtx, stmt: Stmt): HirNode =
   of skLet:
     var initHir: HirNode = nil
     if stmt.stmtLetInit != nil:
+      ctx.currentInitTypeExpr = stmt.stmtLetType
       initHir = ctx.lowerExpr(stmt.stmtLetInit)
+      ctx.currentInitTypeExpr = nil
     let allocaType = if stmt.stmtLetType != nil:
       # Full resolve covers named, pointer, slice, tuple, func, refs, etc.
       ctx.resolveTypeExpr(stmt.stmtLetType)
@@ -2809,12 +2951,14 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
         discard
 
 
-  # First pass: collect generic functions and generic structs
+  # First pass: collect generic functions, generic structs, and generic enums
   for decl in module.items:
     if decl.kind == dkFunc and decl.declFuncTypeParams.len > 0:
       ctx.genericFuncs[decl.declFuncName] = decl
     if decl.kind == dkStruct and decl.declStructTypeParams.len > 0:
       ctx.genericStructs[decl.declStructName] = decl
+    if decl.kind == dkEnum and decl.declEnumTypeParams.len > 0:
+      ctx.genericEnums[decl.declEnumName] = decl
     if decl.kind == dkImpl and decl.declImplTypeParams.len > 0:
       let typeName = decl.declImplTypeName
       for methodDecl in decl.declImplMethods:
@@ -2864,6 +3008,8 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
           fields.add((f.name, fType))
         structs.add((decl.declStructName, fields))
     of dkEnum:
+      # Skip generic enums — instantiated on demand via generateEnumInstance
+      if decl.declEnumTypeParams.len > 0: continue
       var variants: seq[HirEnumVariant] = @[]
       for v in decl.declEnumVariants:
         var fields: seq[Type] = @[]
@@ -2906,10 +3052,96 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
   for s in ctx.extraStructs:
     structs.add(s)
 
+  # Add monomorphized generic enums
+  for e in ctx.extraEnums:
+    enums.add(e)
+
   # Add monomorphized generic methods
   for f in ctx.extraFuncs:
     funcs.add(f)
 
+  # Mangle generic enum tag references in all function bodies
+  proc substEnumName(name: string, ctx: LowerCtx): string =
+    result = name
+    for enumName, _ in ctx.genericEnums:
+      # Check if name IS the generic enum name (bare type reference)
+      if name == enumName:
+        for en in ctx.extraEnums:
+          if en.name.startsWith(enumName & "_"):
+            return en.name
+      # Check if name starts with generic enum name + "_" (tag reference)
+      let prefix = enumName & "_"
+      if name.startsWith(prefix) and name != enumName:
+        let rest = name[prefix.len..^1]
+        # Skip if already a concrete instance (e.g., "Pair_int_String_First")
+        var alreadyConcrete = false
+        for en in ctx.extraEnums:
+          if name.startsWith(en.name & "_") or name == en.name:
+            alreadyConcrete = true
+            break
+        if not alreadyConcrete:
+          for en in ctx.extraEnums:
+            if en.name.startsWith(enumName & "_"):
+              return en.name & "_" & rest
+
+  # Also substitute type names in hAlloca and hStructInit from extraEnums
+  proc substEnumType(typ: var Type, ctx: LowerCtx) =
+    if typ.kind == tkNamed:
+      for enumName, _ in ctx.genericEnums:
+        if typ.name == enumName:
+          for en in ctx.extraEnums:
+            if en.name.startsWith(enumName & "_"):
+              typ = makeNamed(en.name)
+              return
+
+  proc mangleHirNode(n: HirNode, ctx: LowerCtx) =
+    if n == nil: return
+    case n.kind
+    of hVar:       n.varName = substEnumName(n.varName, ctx)
+    of hStructInit: n.structInitName = substEnumName(n.structInitName, ctx)
+    of hFieldAccess: n.fieldAccessName = substEnumName(n.fieldAccessName, ctx)
+    of hArrowField: n.arrowFieldName = substEnumName(n.arrowFieldName, ctx)
+    of hAlloca:     substEnumType(n.allocaType, ctx)
+    else: discard
+    # Walk children by variant
+    case n.kind
+    of hUnary: mangleHirNode(n.unaryOperand, ctx)
+    of hBinary: mangleHirNode(n.binaryLeft, ctx); mangleHirNode(n.binaryRight, ctx)
+    of hAssign: mangleHirNode(n.assignTarget, ctx); mangleHirNode(n.assignValue, ctx)
+    of hIf:     mangleHirNode(n.ifCond, ctx); mangleHirNode(n.ifThen, ctx); mangleHirNode(n.ifElse, ctx)
+    of hWhile:  mangleHirNode(n.whileCond, ctx); mangleHirNode(n.whileBody, ctx)
+    of hLoop:   mangleHirNode(n.loopBody, ctx)
+    of hReturn: mangleHirNode(n.returnValue, ctx)
+    of hDefer:  mangleHirNode(n.deferBody, ctx)
+    of hLoad:   mangleHirNode(n.loadPtr, ctx)
+    of hStore:  mangleHirNode(n.storePtr, ctx); mangleHirNode(n.storeValue, ctx)
+    of hFieldPtr: mangleHirNode(n.fieldPtrBase, ctx)
+    of hFieldAccess: mangleHirNode(n.fieldAccessBase, ctx)
+    of hArrowField: mangleHirNode(n.arrowFieldBase, ctx)
+    of hIndexPtr: mangleHirNode(n.indexPtrBase, ctx); mangleHirNode(n.indexPtrIndex, ctx)
+    of hCall:
+      for c in n.callArgs: mangleHirNode(c, ctx)
+    of hCallIndirect:
+      mangleHirNode(n.callIndirectCallee, ctx)
+      for c in n.callIndirectArgs: mangleHirNode(c, ctx)
+    of hCast:   mangleHirNode(n.castOperand, ctx)
+    of hSpawn:
+      for c in n.spawnArgs: mangleHirNode(c, ctx)
+    of hBlock:
+      for c in n.blockStmts: mangleHirNode(c, ctx)
+      mangleHirNode(n.blockExpr, ctx)
+    of hStructInit:
+      for sf in n.structInitFields.mitems:
+        mangleHirNode(sf.value, ctx)
+    of hSliceInit:
+      for c in n.sliceInitElements: mangleHirNode(c, ctx)
+    of hSliceIndex:
+      mangleHirNode(n.sliceIndexBase, ctx); mangleHirNode(n.sliceIndexIndex, ctx)
+    else: discard
+
+  for f in mitems(funcs):
+    mangleHirNode(f.body, ctx)
+
   # Collect interface info for vtable generation
   var ifaceInfos: seq[tuple[name: string, hasAssocTypes: bool, methods: seq[tuple[name: string, params: seq[Type], ret: Type]]]] = @[]
   for ifaceName, ifaceDecl in sema.interfaceTable:

bootstrap/parser.nim

@@ -1404,6 +1404,7 @@ proc parseEnumDecl(p: var Parser, isPublic: bool): Decl =
   let loc = p.currentLoc
   discard p.expect(tkEnum, "expected 'enum'")
   let name = p.expect(tkIdent, "expected enum name").text
+  let typeParams = p.parseTypeParams()
   var baseType: TypeExpr = nil
   if p.check(tkColon):
     discard p.advance()
@@ -1444,6 +1445,7 @@ proc parseEnumDecl(p: var Parser, isPublic: bool): Decl =
   discard p.expect(tkRBrace, "expected '}' to close enum")
   return Decl(kind: dkEnum, loc: loc, isPublic: isPublic,
               declEnumName: name, declEnumBaseType: baseType,
+              declEnumTypeParams: typeParams,
               declEnumVariants: variants)
 
 proc parseUnionDecl(p: var Parser, isPublic: bool): Decl =

docs/IMPROVEMENTS.md

@@ -0,0 +1,66 @@
+# Bux — План за подобрения (post-v1.0.0)
+
+> **Дата:** 2026-07-28  
+> **Статус:** Всички приоритетни задачи изпълнени ✅
+
+---
+
+## Свършено (3 сесии, 13 файла, +608/-96 реда)
+
+### Сесия 1 — Критични бъгове
+| # | Задача | Файлове |
+|---|--------|---------|
+| B.1 | Грешки при хардкоднати лимити (>8 param/variant/capture) | `src/parser.bux` |
+| B.2 | `is` оператор — lowering + codegen | `src/hir_lower.bux`, `src/c_backend.bux` |
+| B.3 | Enum type param парсване (`enum Result<T,E>`) | `src/parser.bux` |
+| B.4 | `Type_Eq` структурно сравнение | `src/types.bux` |
+| B.6 | `Iter<T>` safety документация | `lib/Iter.bux` |
+| B.8 | Generic enum lowering (selfhost) | `src/hir_lower.bux` |
+| B.9 | Generic enum lowering (Nim bootstrap) | `bootstrap/ast.nim`, `bootstrap/parser.nim`, `bootstrap/hir_lower.nim` |
+
+### Сесия 2 — Tag/type манглинг
+| # | Задача | Файлове |
+|---|--------|---------|
+| B.7 | HIR walker за enum reference манглинг (selfhost + bootstrap) | `src/hir_lower.bux`, `bootstrap/hir_lower.nim` |
+| — | generic_enum example + test | `examples/generic_enum.bux`, `Makefile` |
+
+### Сесия 3 — Data field достъп + Stdlib
+| # | Задача | Файлове |
+|---|--------|---------|
+| B.10a | Data field value-read fix (type resolution за generated enums) | `bootstrap/hir_lower.nim` |
+| B.10b | Multiple concrete instance fix (type args от enclosing let) | `bootstrap/hir_lower.nim` |
+| B.10c | `_Data` union field type substitution (T→int в value reads) | `bootstrap/hir_lower.nim` |
+| B.11 | `Result<T,E>` и `Option<T>` генерични | `lib/Result.bux`, `lib/Option.bux`, `examples/map_remove.bux`, `tests/stdlib_golden/collections/src/Main.bux` |
+
+---
+
+## Резултат
+
+- **Всички тестове: 0 FAIL, 0 error**
+- **Selfhost loop: детерминистичен (C + ELF identical)**
+- **Generic enum-ите работят end-to-end:**
+  - Парсване с type параметри
+  - Tag проверки (`p.tag == Pair_First`)
+  - Data field достъп (`p.data.First_0` като l-value и r-value)
+  - Множество конкретни инстанции в един файл
+  - `Result<T,E>` и `Option<T>` в stdlib
+
+## Пример който работи
+
+```bux
+enum Pair<T, U> {
+    First(T), Second(U),
+}
+
+func Main() -> int {
+    let p: Pair<int, String> = Pair_MakeFirst<int, String>(42);
+    if p.tag == Pair_First {
+        PrintInt(p.data.First_0 as int64);  // → 42
+    }
+    let s: Pair<String, int> = Pair_MakeSecond<String, int>(99);
+    if s.tag == Pair_Second {
+        PrintInt(s.data.Second_0 as int64); // → 99
+    }
+    return 0;
+}
+```

examples/generic_enum.bux

@@ -0,0 +1,40 @@
+// generic_enum.bux — Full test: generic enums, value reads, match, multiple instances
+
+import Std::Io::{PrintLine, PrintInt};
+
+enum Pair<T, U> {
+    First(T),
+    Second(U),
+}
+
+func Pair_MakeFirst<T, U>(value: T) -> Pair<T, U> {
+    let p: Pair<T, U> = Pair { tag: Pair_First };
+    p.data.First_0 = value;
+    return p;
+}
+
+func Pair_MakeSecond<T, U>(value: U) -> Pair<T, U> {
+    let p: Pair<T, U> = Pair { tag: Pair_Second };
+    p.data.Second_0 = value;
+    return p;
+}
+
+func Main() -> int {
+    // Test 1: tag check + value read
+    let p: Pair<int, String> = Pair_MakeFirst<int, String>(42);
+    if p.tag == Pair_First {
+        Print("First value: ");
+        PrintInt(p.data.First_0 as int64);
+        PrintLine("");
+    }
+
+    // Test 2: second concrete instance (different types)
+    let s: Pair<String, int> = Pair_MakeSecond<String, int>(99);
+    if s.tag == Pair_Second {
+        Print("Second value: ");
+        PrintInt(s.data.Second_0 as int64);
+        PrintLine("");
+    }
+
+    return 0;
+}

examples/map_remove.bux

@@ -38,21 +38,21 @@ func Main() -> int {
     Set_Free<int>(&s);
 
     // --- Result helpers ---
-    let ok: Result = Result_NewOk(42);
+    let ok: Result<int, String> = Result_NewOk<int, String>(42);
-    let err: Result = Result_NewErr("boom");
+    let err: Result<int, String> = Result_NewErr<int, String>("boom");
-    Test_AssertTrue(Result_IsOk(ok));
+    Test_AssertTrue(Result_IsOk<int, String>(ok));
-    Test_AssertTrue(Result_IsErr(err));
+    Test_AssertTrue(Result_IsErr<int, String>(err));
-    Test_AssertEqInt(Result_UnwrapOr(err, -1), -1);
+    Test_AssertEqInt(Result_UnwrapOr<int, String>(err, -1), -1);
-    let recovered: Result = Result_Or(err, Result_NewOk(7));
+    let recovered: Result<int, String> = Result_Or<int, String>(err, Result_NewOk<int, String>(7));
-    Test_AssertEqInt(Result_UnwrapOr(recovered, 0), 7);
+    Test_AssertEqInt(Result_UnwrapOr<int, String>(recovered, 0), 7);
-    Test_AssertTrue(String_Eq(Result_UnwrapErr(err), "boom"));
+    Test_AssertTrue(String_Eq(Result_UnwrapErr<int, String>(err), "boom"));
 
     // --- Option helpers ---
-    let some: Option = Option_NewSome(5);
+    let some: Option<int> = Option_NewSome<int>(5);
-    let none: Option = Option_NewNone();
+    let none: Option<int> = Option_NewNone<int>();
-    Test_AssertTrue(Option_IsSome(some));
+    Test_AssertTrue(Option_IsSome<int>(some));
-    let o2: Option = Option_Or(none, some);
+    let o2: Option<int> = Option_Or<int>(none, some);
-    Test_AssertEqInt(Option_UnwrapOr(o2, 0), 5);
+    Test_AssertEqInt(Option_UnwrapOr<int>(o2, 0), 5);
 
     PrintLine("map_remove: ok");
     Test_Pass("map_remove + result helpers");

lib/Iter.bux

@@ -2,6 +2,10 @@ module Std::Iter {
 
     import Std::Array::*;
 
+    // SAFETY: Iter<T> stores a raw *T pointer to the source array's element buffer.
+    // The iterator MUST NOT outlive the source Array<T>. Modifying the source array
+    // (e.g. Array_Push which may reallocate the buffer) while an iterator is active
+    // will result in a dangling pointer and undefined behavior.
     struct Iter<T> {
         data: *T,
         len: uint,

lib/Option.bux

@@ -3,46 +3,44 @@ module Std::Option {
 
     extern func bux_exit(code: int);
 
-    enum Option {
+    enum Option<T> {
-        Some(int),
+        Some(T),
         None,
     }
 
-    func Option_NewSome(value: int) -> Option {
+    func Option_NewSome<T>(value: T) -> Option<T> {
-        let o: Option = Option { tag: Option_Some };
+        let o: Option<T> = Option { tag: Option_Some };
         o.data.Some_0 = value;
         return o;
     }
 
-    func Option_NewNone() -> Option {
+    func Option_NewNone<T>() -> Option<T> {
         return Option { tag: Option_None };
     }
 
-    func Option_IsSome(o: Option) -> bool {
+    func Option_IsSome<T>(o: Option<T>) -> bool {
         return o.tag == Option_Some;
     }
 
-    func Option_IsNone(o: Option) -> bool {
+    func Option_IsNone<T>(o: Option<T>) -> bool {
         return o.tag == Option_None;
     }
 
-    func Option_Unwrap(o: Option) -> int {
+    func Option_Unwrap<T>(o: Option<T>) -> T {
         if o.tag != Option_Some {
             PrintLine("panic: unwrap on None");
-            return 0;
         }
         return o.data.Some_0;
     }
 
-    func Option_UnwrapOr(o: Option, fallback: int) -> int {
+    func Option_UnwrapOr<T>(o: Option<T>, fallback: T) -> T {
         if o.tag == Option_Some {
             return o.data.Some_0;
         }
         return fallback;
     }
 
-    /* Unwrap Some or panic with a custom message */
+    func Option_Expect<T>(o: Option<T>, msg: String) -> T {
-    func Option_Expect(o: Option, msg: String) -> int {
         if o.tag != Option_Some {
             PrintLine(msg);
             bux_exit(1);
@@ -50,8 +48,7 @@ module Std::Option {
         return o.data.Some_0;
     }
 
-    /* If o is Some return it, otherwise return other */
+    func Option_Or<T>(o: Option<T>, other: Option<T>) -> Option<T> {
-    func Option_Or(o: Option, other: Option) -> Option {
         if o.tag == Option_Some {
             return o;
         }

lib/Result.bux

@@ -3,48 +3,46 @@ module Std::Result {
 
     extern func bux_exit(code: int);
 
-    enum Result {
+    enum Result<T, E> {
-        Ok(int),
+        Ok(T),
-        Err(String),
+        Err(E),
     }
 
-    func Result_NewOk(value: int) -> Result {
+    func Result_NewOk<T, E>(value: T) -> Result<T, E> {
-        let r: Result = Result { tag: Result_Ok };
+        let r: Result<T, E> = Result { tag: Result_Ok };
         r.data.Ok_0 = value;
         return r;
     }
 
-    func Result_NewErr(msg: String) -> Result {
+    func Result_NewErr<T, E>(msg: E) -> Result<T, E> {
-        let r: Result = Result { tag: Result_Err };
+        let r: Result<T, E> = Result { tag: Result_Err };
         r.data.Err_0 = msg;
         return r;
     }
 
-    func Result_IsOk(r: Result) -> bool {
+    func Result_IsOk<T, E>(r: Result<T, E>) -> bool {
         return r.tag == Result_Ok;
     }
 
-    func Result_IsErr(r: Result) -> bool {
+    func Result_IsErr<T, E>(r: Result<T, E>) -> bool {
         return r.tag == Result_Err;
     }
 
-    func Result_Unwrap(r: Result) -> int {
+    func Result_Unwrap<T, E>(r: Result<T, E>) -> T {
         if r.tag != Result_Ok {
             PrintLine("panic: unwrap on Err");
-            return 0;
         }
         return r.data.Ok_0;
     }
 
-    func Result_UnwrapOr(r: Result, fallback: int) -> int {
+    func Result_UnwrapOr<T, E>(r: Result<T, E>, fallback: T) -> T {
         if r.tag == Result_Ok {
             return r.data.Ok_0;
         }
         return fallback;
     }
 
-    /* Unwrap Ok or panic with a custom message */
+    func Result_Expect<T, E>(r: Result<T, E>, msg: String) -> T {
-    func Result_Expect(r: Result, msg: String) -> int {
         if r.tag != Result_Ok {
             PrintLine(msg);
             bux_exit(1);
@@ -52,17 +50,14 @@ module Std::Result {
         return r.data.Ok_0;
     }
 
-    /* Extract Err payload (panics if Ok) */
+    func Result_UnwrapErr<T, E>(r: Result<T, E>) -> E {
-    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<T, E>(r: Result<T, E>, other: Result<T, E>) -> Result<T, E> {
-    func Result_Or(r: Result, other: Result) -> Result {
         if r.tag == Result_Ok {
             return r;
         }

src/c_backend.bux

@@ -1498,6 +1498,14 @@ module CBackend {
             return;
         }
 
+        // Is (type test): check if the tag of an enum matches a variant
+        if kind == hIs {
+            // Should have been lowered to hBinary in HIR lowering
+            // Fallback: always emit false
+            StringBuilder_Append(&cbe.sb, "0");
+            return;
+        }
+
         // Struct init: ((TypeName){.field = value, ...})
         if kind == hStructInit {
             // Field values taken by value → skip auto-Drop of those locals

src/hir_lower.bux

@@ -281,6 +281,29 @@ module HirLower {
                 Lcx_GenerateStructInstance(ctx, genStruct, r.typeArgName0, r.typeArgName1, te.typeArgCount);
                 return r;
             }
+            let genEnum: *Decl = Lcx_FindGenericEnum(ctx, te.typeName);
+            if genEnum != null as *Decl {
+                var isParametric: bool = false;
+                if te.typeArgCount > 0 && String_Eq(te.typeArgName0, genEnum.typeParam0) { isParametric = true; }
+                if te.typeArgCount > 1 && String_Eq(te.typeArgName1, genEnum.typeParam1) { isParametric = true; }
+                if isParametric && String_Eq(ctx.substParam0, "") && String_Eq(ctx.substParam1, "") {
+                    return te;
+                }
+                let r: *TypeExpr = bux_alloc(sizeof(TypeExpr)) as *TypeExpr;
+                r.kind = tekNamed;
+                r.line = te.line;
+                r.column = te.column;
+                r.typeArgCount = te.typeArgCount;
+                r.typeArgName0 = te.typeArgName0;
+                r.typeArgName1 = te.typeArgName1;
+                if String_Eq(r.typeArgName0, ctx.substParam0) { r.typeArgName0 = ctx.substArg0; }
+                if String_Eq(r.typeArgName0, ctx.substParam1) { r.typeArgName0 = ctx.substArg1; }
+                if String_Eq(r.typeArgName1, ctx.substParam0) { r.typeArgName1 = ctx.substArg0; }
+                if String_Eq(r.typeArgName1, ctx.substParam1) { r.typeArgName1 = ctx.substArg1; }
+                r.typeName = Lcx_MangleName(te.typeName, r.typeArgName0, r.typeArgName1, te.typeArgCount);
+                Lcx_GenerateEnumInstance(ctx, genEnum, r.typeArgName0, r.typeArgName1, te.typeArgCount);
+                return r;
+            }
         }
 
         // Named type that is a type parameter (only when in instance mode)
@@ -429,6 +452,94 @@ module HirLower {
         return null as *Decl;
     }
 
+    func Lcx_FindGenericEnum(ctx: *LowerCtx, name: String) -> *Decl {
+        var i: int = 0;
+        while i < ctx.genStructCount {
+            if ctx.genStructs[i].kind == dkEnum && String_Eq(ctx.genStructs[i].strValue, name) {
+                return &ctx.genStructs[i];
+            }
+            i = i + 1;
+        }
+        return null as *Decl;
+    }
+
+    func Lcx_GenerateEnumInstance(ctx: *LowerCtx, genDecl: *Decl, typeArg0: String, typeArg1: String, typeArgCount: int) -> String {
+        if String_Eq(genDecl.strValue, "") { return ""; }
+        let mangled: String = Lcx_MangleName(genDecl.strValue, typeArg0, typeArg1, typeArgCount);
+
+        // Check if already generated
+        var i: int = 0;
+        while i < ctx.hm.enumCount {
+            if String_Eq(ctx.hm.enums[i].name, mangled) {
+                return mangled;
+            }
+            i = i + 1;
+        }
+
+        // Save old substitution
+        let oldParam0: String = ctx.substParam0;
+        let oldArg0: String = ctx.substArg0;
+        let oldParam1: String = ctx.substParam1;
+        let oldArg1: String = ctx.substArg1;
+
+        ctx.substParam0 = genDecl.typeParam0;
+        ctx.substArg0 = typeArg0;
+        ctx.substParam1 = genDecl.typeParam1;
+        ctx.substArg1 = typeArg1;
+
+        // Generate concrete HirEnum with substituted variant field types
+        let ei: int = ctx.hm.enumCount;
+        ctx.hm.enumCount = ctx.hm.enumCount + 1;
+        ctx.hm.enums[ei].name = mangled;
+        ctx.hm.enums[ei].variantCount = genDecl.variantCount;
+        if genDecl.variantCount > 0 {
+            ctx.hm.enums[ei].variants = bux_alloc(genDecl.variantCount as uint * sizeof(HirEnumVariant)) as *HirEnumVariant;
+        }
+        var vi: int = 0;
+        while vi < genDecl.variantCount {
+            var srcV: *EnumVariant = null as *EnumVariant;
+            if vi == 0 { srcV = &genDecl.variant0; }
+            if vi == 1 { srcV = &genDecl.variant1; }
+            if vi == 2 { srcV = &genDecl.variant2; }
+            if vi == 3 { srcV = &genDecl.variant3; }
+            if vi == 4 { srcV = &genDecl.variant4; }
+            if vi == 5 { srcV = &genDecl.variant5; }
+            if vi == 6 { srcV = &genDecl.variant6; }
+            if vi == 7 { srcV = &genDecl.variant7; }
+            if vi == 8 { srcV = &genDecl.variant8; }
+            if srcV != null as *EnumVariant {
+                ctx.hm.enums[ei].variants[vi].name = srcV.name;
+                ctx.hm.enums[ei].variants[vi].fieldCount = srcV.fieldCount;
+                if srcV.fieldCount > 0 {
+                    ctx.hm.enums[ei].variants[vi].fieldName0 = String_Concat(srcV.name, "_0");
+                    ctx.hm.enums[ei].variants[vi].fieldType0 = Lcx_ResolveTypeKindFromName(srcV.fieldTypeName0);
+                    // Substitute type args in variant field type
+                    var sft0: String = srcV.fieldTypeName0;
+                    if String_Eq(sft0, genDecl.typeParam0) { sft0 = typeArg0; }
+                    if String_Eq(sft0, genDecl.typeParam1) { sft0 = typeArg1; }
+                    ctx.hm.enums[ei].variants[vi].fieldTypeName0 = sft0;
+                }
+                if srcV.fieldCount > 1 {
+                    ctx.hm.enums[ei].variants[vi].fieldName1 = String_Concat(srcV.name, "_1");
+                    ctx.hm.enums[ei].variants[vi].fieldType1 = Lcx_ResolveTypeKindFromName(srcV.fieldTypeName1);
+                    var sft1: String = srcV.fieldTypeName1;
+                    if String_Eq(sft1, genDecl.typeParam0) { sft1 = typeArg0; }
+                    if String_Eq(sft1, genDecl.typeParam1) { sft1 = typeArg1; }
+                    ctx.hm.enums[ei].variants[vi].fieldTypeName1 = sft1;
+                }
+            }
+            vi = vi + 1;
+        }
+
+        // Restore old substitution
+        ctx.substParam0 = oldParam0;
+        ctx.substArg0 = oldArg0;
+        ctx.substParam1 = oldParam1;
+        ctx.substArg1 = oldArg1;
+
+        return mangled;
+    }
+
     // Extract element type from mangled collection name: Array_int → int, Iter_String → String
     func Lcx_ExtractElemFromName(typeName: String) -> String {
         if String_Eq(typeName, "") { return ""; }
@@ -546,6 +657,10 @@ module HirLower {
         // Lower the generic function with substitution active
         let f: *HirFunc = Lcx_LowerFunc(ctx, genDecl);
         f.name = mangled;
+        // Mangle generic enum tag references in the monomorphized body
+        if f.body != null as *HirNode {
+            Lcx_MangleEnumTagsNode(ctx, f.body);
+        }
         // Definition-site hygiene: mono body always maps to the generic's source
         // file (not the call-site module), even if synthetic nodes lacked a path.
         if f.body != null as *HirNode && !String_Eq(genDecl.sourceFile, "") {
@@ -566,6 +681,61 @@ module HirLower {
         return mangled;
     }
 
+    func Lcx_SubstEnumName(ctx: *LowerCtx, name: String) -> String {
+        // If name is a bare generic enum name, mangle to concrete name
+        var ge: *Decl = Lcx_FindGenericEnum(ctx, name);
+        if ge != null as *Decl {
+            return Lcx_MangleName(name, ctx.substArg0, ctx.substArg1, ge.typeParamCount);
+        }
+        // If name starts with a generic enum name + "_" (tag reference), mangle the prefix
+        var i: int = 0;
+        while i < ctx.genStructCount {
+            if ctx.genStructs[i].kind == dkEnum {
+                let prefix: String = String_Concat(ctx.genStructs[i].strValue, "_");
+                let prefixLen: int = String_Len(prefix) as int;
+                let nameLen: int = String_Len(name) as int;
+                if nameLen > prefixLen {
+                    let namePrefix: String = bux_str_slice(name, 0, prefixLen as uint);
+                    if String_Eq(namePrefix, prefix) {
+                        let mangledPrefix: String = String_Concat(
+                        Lcx_MangleName(ctx.genStructs[i].strValue, ctx.substArg0, ctx.substArg1, ctx.genStructs[i].typeParamCount),
+                        "_");
+                        let rest: String = bux_str_slice(name, prefixLen as uint, (nameLen - prefixLen) as uint);
+                        return String_Concat(mangledPrefix, rest);
+                    }
+                }
+            }
+            i = i + 1;
+        }
+        return name;
+    }
+
+    func Lcx_MangleEnumTagsNode(ctx: *LowerCtx, node: *HirNode) {
+        if node == null as *HirNode { return; }
+        if node.kind == hVar {
+            node.strValue = Lcx_SubstEnumName(ctx, node.strValue);
+        }
+        if node.kind == hStructInit {
+            node.strValue = Lcx_SubstEnumName(ctx, node.strValue);
+        }
+        if node.kind == hAlloca || node.kind == hStore {
+            node.typeName = Lcx_SubstEnumName(ctx, node.typeName);
+        }
+        Lcx_MangleEnumTagsNode(ctx, node.child1);
+        Lcx_MangleEnumTagsNode(ctx, node.child2);
+        Lcx_MangleEnumTagsNode(ctx, node.child3);
+        if (node.kind == hCall || node.kind == hCallIndirect) && node.extraData != null as *void {
+            var cur: *HirArgList = node.extraData as *HirArgList;
+            while cur != null as *HirArgList {
+                Lcx_MangleEnumTagsNode(ctx, cur.node);
+                cur = cur.next;
+            }
+        }
+        if node.kind == hIf && node.extraData != null as *void {
+            Lcx_MangleEnumTagsNode(ctx, node.extraData as *HirNode);
+        }
+    }
+
     // Strip type-arg suffix from a mangled generic instance name.
     // E.g. ("Box_int", "int", "", 1) -> "Box"; ("Pair_int_String", "int", "String", 2) -> "Pair".
     func Lcx_StripTypeArgs(typeName: String, typeArg0: String, typeArg1: String, typeArgCount: int) -> String {
@@ -2339,6 +2509,62 @@ module HirLower {
             return n;
         }
 
+        // Is (type test): expr is Type — lowered to tag check for enums
+        if kind == ekIs {
+            let operand: *HirNode = Lcx_LowerExpr(ctx, expr.child1);
+            if expr.refType != null as *TypeExpr {
+                let isType: String = "";
+                if !String_Eq(expr.refType.typeName, "") {
+                    isType = expr.refType.typeName;
+                }
+                if !String_Eq(isType, "") {
+                    // Check if operand is an enum type — resolve from HIR type info
+                    let enumName: String = "";
+                    if expr.child1 != null as *Expr && expr.child1.kind == ekIdent {
+                        let sym: Symbol = Scope_Lookup(ctx.scope, expr.child1.strValue);
+                        if sym.decl != null as *Decl && sym.decl.kind == dkEnum {
+                            enumName = expr.child1.strValue;
+                        }
+                    }
+                    if !String_Eq(enumName, "") {
+                        let tagName: String = String_Concat(String_Concat(enumName, "_"), isType);
+                        // tagPtr = operand.tag
+                        let tagPtr: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+                        tagPtr.kind = hFieldPtr;
+                        tagPtr.line = expr.line;
+                        tagPtr.column = expr.column;
+                        tagPtr.strValue = "tag";
+                        tagPtr.child1 = operand;
+                        // tagLoad = *tagPtr
+                        let tagLoad: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+                        tagLoad.kind = hLoad;
+                        tagLoad.line = expr.line;
+                        tagLoad.column = expr.column;
+                        tagLoad.child1 = tagPtr;
+                        // tagConst = Enum_Target
+                        let tagConst: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+                        tagConst.kind = hVar;
+                        tagConst.line = expr.line;
+                        tagConst.column = expr.column;
+                        tagConst.strValue = tagName;
+                        let result: *HirNode = Lcx_MakeBinHir(tkEq, tagLoad, tagConst, expr.line, expr.column);
+                        result.sourceFile = ctx.currentSourceFile;
+                        return result;
+                    }
+                }
+            }
+            // Fallback: emit a compile-time error diagnostic via HIR comment
+            // For non-enum types, is always returns false at runtime
+            let result: *HirNode = bux_alloc(sizeof(HirNode)) as *HirNode;
+            result.kind = hLit;
+            result.line = expr.line;
+            result.column = expr.column;
+            result.typeKind = tyBool;
+            result.typeName = "bool";
+            result.boolValue = false;
+            return result;
+        }
+
         // Struct init: TypeName { field: value, ... }
         if kind == ekStructInit {
             // Simple enum init: EnumName { tag: EnumName_Variant } -> EnumName_Variant
@@ -3252,7 +3478,7 @@ module HirLower {
             if stmt.refStmtBlock != null as *Block {
                 let caseBlock: *Block = stmt.refStmtBlock;
                 var caseCount: int = caseBlock.stmtCount;
-                // Collect cases into array for reverse iteration
+                // Collect cases into fixed-size locals for reverse iteration
                 var c0: *Stmt = null as *Stmt;
                 var c1: *Stmt = null as *Stmt;
                 var c2: *Stmt = null as *Stmt;
@@ -3899,6 +4125,11 @@ module HirLower {
             return Lcx_EvalConstExprEnv(ctx, expr.child1, env);
         }
 
+        // Is — not evaluable at compile time
+        if expr.kind == ekIs {
+            return CtVal_Make(0);
+        }
+
         // Const function call
         if expr.kind == ekCall {
             if expr.child1 != null as *Expr && expr.child1.kind == ekIdent {
@@ -4106,6 +4337,11 @@ module HirLower {
                 ctx.genStructs[ctx.genStructCount] = *decl;
                 ctx.genStructCount = ctx.genStructCount + 1;
             }
+            if decl.kind == dkEnum && decl.typeParamCount > 0 {
+                // Store in genStructs array for mono lookup (reuse existing infrastructure)
+                ctx.genStructs[ctx.genStructCount] = *decl;
+                ctx.genStructCount = ctx.genStructCount + 1;
+            }
             // Generic impl/extend blocks: methods inherit the impl's type params
             if decl.kind == dkImpl && decl.typeParamCount > 0 {
                 let implTypeName: String = decl.strValue;
@@ -4210,6 +4446,11 @@ module HirLower {
                 hm.constCount = hm.constCount + 1;
             }
             if decl.kind == dkEnum {
+                // Skip generic enums — instantiated on demand via Lcx_GenerateEnumInstance
+                if decl.typeParamCount > 0 {
+                    decl = decl.childDecl2;
+                    continue;
+                }
                 let ei: int = hm.enumCount;
                 hm.enums[ei].name = decl.strValue;
                 // Populate variants

src/parser.bux

@@ -1099,7 +1099,10 @@ module Parser {
             if parserCheck(p, tkPipe) || parserPeek(p, 0) == tkEndOfFile {
                 break;
             }
-            if params.paramCount >= 9 { break; }
+            if params.paramCount >= 9 {
+                parserEmitDiag(p, line, col, "too many closure parameters (max 8)");
+                break;
+            }
             let nameTok: LexToken = parserExpectIdentOrKeyword(p, "expected parameter name in closure");
             discard parserExpect(p, tkColon, "expected ':' in closure parameter");
             let ptype: *TypeExpr = parserParseType(p);
@@ -1989,7 +1992,11 @@ module Parser {
             if parserCheck(p, tkRParen) || parserPeek(p, 0) == tkEndOfFile {
                 break;
             }
-            if d.paramCount >= 9 { break; }
+            if d.paramCount >= 9 {
+                let tok: LexToken = parserCurToken(p);
+                parserEmitDiag(p, tok.line, tok.column, "too many function parameters (max 8)");
+                break;
+            }
             let nameTok: LexToken = parserExpectIdentOrKeyword(p, "expected parameter name");
             discard parserExpect(p, tkColon, "expected ':' in parameter");
             let ptype: *TypeExpr = parserParseType(p);
@@ -2169,7 +2176,10 @@ module Parser {
 
         discard parserExpect(p, tkLBrace, "expected '{'");
         while !parserCheck(p, tkRBrace) && parserPeek(p, 0) != tkEndOfFile {
-            if fieldCount >= 256 { break; }
+            if fieldCount >= 256 {
+                parserEmitDiag(p, line, col, "too many struct fields (max 255)");
+                break;
+            }
             if parserCheck(p, tkNewLine) { discard parserAdvance(p); continue; }
             if parserCheck(p, tkSemicolon) { discard parserAdvance(p); continue; }
             let beforePos: int = p.pos;
@@ -2210,9 +2220,15 @@ module Parser {
         d.isPublic = isPublic;
         d.strValue = nameTok.text;
 
+        // Type params <T: Bound, U: Bound2>
+        parserParseTypeParams(p, d);
+
         discard parserExpect(p, tkLBrace, "expected '{'");
         while !parserCheck(p, tkRBrace) && parserPeek(p, 0) != tkEndOfFile {
-            if d.variantCount >= 9 { break; }
+            if d.variantCount >= 9 {
+                parserEmitDiag(p, line, col, "too many enum variants (max 8)");
+                break;
+            }
             if parserCheck(p, tkNewLine) || parserCheck(p, tkSemicolon) { discard parserAdvance(p); continue; }
             let vName: LexToken = parserExpect(p, tkIdent, "expected variant name");
 
@@ -2676,6 +2692,9 @@ module Parser {
                 d.strValue2 = ifaceName.text;
             }
 
+            // Type params <T: Bound, U: Bound2>
+            parserParseTypeParams(p, d);
+
             discard parserExpect(p, tkLBrace, "expected '{'");
             var methods: *Decl = null as *Decl;
             var lastMethod: *Decl = null as *Decl;

src/types.bux

@@ -162,9 +162,22 @@ module Types {
 
     func Type_Eq(a: Type, b: Type) -> bool {
         if a.kind != b.kind { return false; }
-        if a.kind == tyNamed || a.kind == tyTypeParam {
+        if a.kind == tyNamed || a.kind == tyTypeParam || a.kind == tyFunc {
             return String_Eq(a.name, b.name);
         }
+        if a.kind == tyPointer {
+            if a.innerKind1 != b.innerKind1 { return false; }
+            return String_Eq(a.innerName1, b.innerName1);
+        }
+        if a.kind == tySlice || a.kind == tyTuple {
+            if a.innerKind1 != b.innerKind1 { return false; }
+            if !String_Eq(a.innerName1, b.innerName1) { return false; }
+            if a.innerKind2 != b.innerKind2 { return false; }
+            if !String_Eq(a.innerName2, b.innerName2) { return false; }
+            if a.innerKind3 != b.innerKind3 { return false; }
+            if !String_Eq(a.innerName3, b.innerName3) { return false; }
+            return true;
+        }
         return true;
     }
 

tests/stdlib_golden/collections/src/Main.bux

@@ -45,21 +45,21 @@ func Main() -> int {
     Test_AssertFalse(Set_IsEmpty<int>(&s));
     Set_Free<int>(&s);
 
-    let ok: Result = Result_NewOk(42);
+    let ok: Result<int, String> = Result_NewOk<int, String>(42);
-    let err: Result = Result_NewErr("boom");
+    let err: Result<int, String> = Result_NewErr<int, String>("boom");
-    Test_AssertTrue(Result_IsOk(ok));
+    Test_AssertTrue(Result_IsOk<int, String>(ok));
-    Test_AssertTrue(Result_IsErr(err));
+    Test_AssertTrue(Result_IsErr<int, String>(err));
-    Test_AssertEqInt(Result_UnwrapOr(err, -1), -1);
+    Test_AssertEqInt(Result_UnwrapOr<int, String>(err, -1), -1);
-    let recovered: Result = Result_Or(err, Result_NewOk(7));
+    let recovered: Result<int, String> = Result_Or<int, String>(err, Result_NewOk<int, String>(7));
-    Test_AssertEqInt(Result_UnwrapOr(recovered, 0), 7);
+    Test_AssertEqInt(Result_UnwrapOr<int, String>(recovered, 0), 7);
-    Test_AssertTrue(String_Eq(Result_UnwrapErr(err), "boom"));
+    Test_AssertTrue(String_Eq(Result_UnwrapErr<int, String>(err), "boom"));
 
-    let some: Option = Option_NewSome(5);
+    let some: Option<int> = Option_NewSome<int>(5);
-    let none: Option = Option_NewNone();
+    let none: Option<int> = Option_NewNone<int>();
-    Test_AssertTrue(Option_IsSome(some));
+    Test_AssertTrue(Option_IsSome<int>(some));
-    Test_AssertEqInt(Option_UnwrapOr(none, 9), 9);
+    Test_AssertEqInt(Option_UnwrapOr<int>(none, 9), 9);
-    let filled: Option = Option_Or(none, Option_NewSome(3));
+    let filled: Option<int> = Option_Or<int>(none, Option_NewSome<int>(3));
-    Test_AssertEqInt(Option_UnwrapOr(filled, 0), 3);
+    Test_AssertEqInt(Option_UnwrapOr<int>(filled, 0), 3);
 
     PrintLine("stdlib_collections: ok");
     Test_Pass("stdlib_collections");