feat: generic struct monomorphization + tkUnknown fix

- Add generic struct instantiation (Box<int>, Pair<T,U>) in HIR lowering
- Fix tkUnknown/tkNamed/tkTypeParam ambiguity in sema.nim (qualify with TypeKind)
- Add generics_struct example
- Update Makefile with new example

Makefile

@@ -3,7 +3,7 @@ SRC := src/main.nim
 OUT := buxc
 BUILD_DIR := build
 
-EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics pattern_matching strings map result_option try_operator
+EXAMPLES := hello fibonacci factorial structs enums methods algebraic_enums generics pattern_matching strings map result_option try_operator generics_struct
 
 .PHONY: all build dev test clean test-examples
 

examples/generics_struct.bux

@@ -0,0 +1,25 @@
+// Generic structs - Box<T> and Pair<T, U>
+import Std::Io::{PrintLine, PrintInt};
+
+struct Box<T> {
+    value: T,
+}
+
+struct Pair<T, U> {
+    first: T,
+    second: U,
+}
+
+func Main() -> int {
+    let b: Box<int> = Box<int> { value: 42 };
+    PrintLine("Box value:");
+    PrintInt(b.value);
+    PrintLine("");
+    
+    let p: Pair<int, String> = Pair<int, String> { first: 10, second: "hello" };
+    PrintLine("Pair first:");
+    PrintInt(p.first);
+    PrintLine("");
+    
+    return 0;
+}

src/hir_lower.nim

@@ -13,6 +13,9 @@ type
     pendingStmts*: seq[HirNode]
     typeSubst*: Table[string, Type]  # Type parameter substitution for generics
     importTable*: Table[string, string]  # Local name → fully qualified name for imports
+    genericStructs*: Table[string, Decl]  # Generic struct declarations
+    generatedStructInsts*: Table[string, bool]  # Track generated struct instantiations
+    extraStructs*: seq[tuple[name: string, fields: seq[tuple[name: string, typ: Type]]]]
 
 proc freshName(ctx: var LowerCtx): string =
   inc ctx.varCounter
@@ -118,11 +121,71 @@ proc initLowerCtx*(module: Module, sema: Sema): LowerCtx =
   result.pendingStmts = @[]
   result.typeSubst = initTable[string, Type]()
   result.importTable = initTable[string, string]()
+  result.genericStructs = initTable[string, Decl]()
+  result.generatedStructInsts = initTable[string, bool]()
+  result.extraStructs = @[]
+
+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
+  of tekNamed:
+    if subst.hasKey(te.typeName):
+      return subst[te.typeName]
+    if te.typeArgs.len > 0 and ctx.genericStructs.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.generatedStructInsts.hasKey(mangledName):
+        let genericDecl = ctx.genericStructs[te.typeName]
+        var fields: seq[tuple[name: string, typ: Type]] = @[]
+        for f in genericDecl.declStructFields:
+          let resolvedType = substituteType(ctx, f.ftype, subst)
+          fields.add((f.name, resolvedType))
+        ctx.extraStructs.add((mangledName, fields))
+        ctx.generatedStructInsts[mangledName] = true
+      return makeNamed(mangledName)
+    return ctx.resolveTypeExpr(te)
+  of tekPointer:
+    return makePointer(substituteType(ctx, te.pointerPointee, subst))
+  of tekSlice:
+    return makeSlice(substituteType(ctx, te.sliceElement, subst))
+  of tekTuple:
+    var elems: seq[Type] = @[]
+    for e in te.tupleElements:
+      elems.add(substituteType(ctx, e, subst))
+    return makeTuple(elems)
+  else:
+    return ctx.resolveTypeExpr(te)
 
 proc resolveTypeExpr(ctx: var LowerCtx, te: TypeExpr): Type =
   if te == nil: return makeUnknown()
   case te.kind
   of tekNamed:
+    if te.typeArgs.len > 0 and ctx.genericStructs.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.generatedStructInsts.hasKey(mangledName):
+        let genericDecl = ctx.genericStructs[te.typeName]
+        var fields: seq[tuple[name: string, typ: Type]] = @[]
+        var subst = initTable[string, Type]()
+        for j, tp in genericDecl.declStructTypeParams:
+          if j < te.typeArgs.len:
+            subst[tp] = ctx.resolveTypeExpr(te.typeArgs[j])
+        for f in genericDecl.declStructFields:
+          let resolvedType = substituteType(ctx, f.ftype, subst)
+          fields.add((f.name, resolvedType))
+        ctx.extraStructs.add((mangledName, fields))
+        ctx.generatedStructInsts[mangledName] = true
+      return makeNamed(mangledName)
     case te.typeName
     of "void": return makeVoid()
     of "bool": return makeBool()
@@ -252,7 +315,11 @@ proc resolveExprType(ctx: var LowerCtx, expr: Expr): Type =
                 return ctx.resolveTypeExpr(f.ftype)
               else: return makeUnknown()
     return makeUnknown()
-  of ekStructInit: return makeNamed(expr.exprStructInitName)
+  of ekStructInit:
+    if expr.exprStructInitTypeArgs.len > 0:
+      let te = TypeExpr(kind: tekNamed, loc: expr.loc, typeName: expr.exprStructInitName, typeArgs: expr.exprStructInitTypeArgs)
+      return ctx.resolveTypeExpr(te)
+    return makeNamed(expr.exprStructInitName)
   of ekSlice:
     if expr.exprSliceElements.len > 0:
       return makeSlice(ctx.resolveExprType(expr.exprSliceElements[0]))
@@ -405,7 +472,15 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
     var fields: seq[tuple[name: string, value: HirNode]] = @[]
     for f in expr.exprStructInitFields:
       fields.add((f.name, ctx.lowerExpr(f.value)))
-    return HirNode(kind: hStructInit, structInitName: expr.exprStructInitName,
+    var structName = expr.exprStructInitName
+    if expr.exprStructInitTypeArgs.len > 0:
+      var suffix = ""
+      for i, targ in expr.exprStructInitTypeArgs:
+        if i > 0: suffix.add("_")
+        let argType = ctx.resolveTypeExpr(targ)
+        suffix.add(argType.toString)
+      structName = structName & "_" & suffix
+    return HirNode(kind: hStructInit, structInitName: structName,
                    structInitFields: fields, typ: typ, loc: loc)
 
   of ekSlice:
@@ -801,11 +876,13 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
         discard
 
 
-  # First pass: collect generic functions
+  # First pass: collect generic functions and generic structs
   var genericFuncs = initTable[string, Decl]()
   for decl in module.items:
     if decl.kind == dkFunc and decl.declFuncTypeParams.len > 0:
       genericFuncs[decl.declFuncName] = decl
+    if decl.kind == dkStruct and decl.declStructTypeParams.len > 0:
+      ctx.genericStructs[decl.declStructName] = decl
 
   # Second pass: find all generic calls and monomorphize
   proc findGenericCalls(expr: Expr): seq[tuple[name: string, typeArgs: seq[TypeExpr]]] =
@@ -932,6 +1009,7 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
           hf.name = decl.declImplTypeName & "_" & hf.name
           funcs.add(hf)
     of dkStruct:
+      if decl.declStructTypeParams.len == 0:  # Skip generic structs — monomorphized separately
         var fields: seq[tuple[name: string, typ: Type]] = @[]
         for f in decl.declStructFields:
           let fType = if f.ftype != nil: ctx.resolveTypeExpr(f.ftype) else: makeUnknown()
@@ -980,4 +1058,8 @@ proc lowerModule*(module: Module, sema: Sema): HirModule =
       consts.add((decl.declConstName, typ, value))
     else: discard
 
+  # Add monomorphized generic structs
+  for s in ctx.extraStructs:
+    structs.add(s)
+
   result = HirModule(funcs: funcs, externFuncs: externFuncs, structs: structs, enums: enums, consts: consts)

src/parser.nim

@@ -503,7 +503,7 @@ proc parsePostfix(p: var Parser): Expr =
       discard p.advance()
       left = Expr(kind: ekTry, loc: loc, exprTryOperand: left, exprTryType: nil)
     of tkLBrace:
-      if p.structInitAllowed and left.kind in {ekIdent, ekPath}:
+      if p.structInitAllowed and left.kind in {ekIdent, ekPath, ekGenericCall}:
         discard p.advance()
         var fields: seq[tuple[name: string, value: Expr]] = @[]
         while not p.check(tkRBrace) and not p.isAtEnd:
@@ -514,8 +514,17 @@ proc parsePostfix(p: var Parser): Expr =
           if p.check(tkComma):
             discard p.advance()
         discard p.expect(tkRBrace, "expected '}'")
-        let typeName = if left.kind == ekIdent: left.exprIdent else: left.exprPath.join("::")
-        left = Expr(kind: ekStructInit, loc: loc, exprStructInitName: typeName, exprStructInitFields: fields)
+        var typeName = ""
+        var typeArgs: seq[TypeExpr] = @[]
+        if left.kind == ekIdent:
+          typeName = left.exprIdent
+        elif left.kind == ekPath:
+          typeName = left.exprPath.join("::")
+        elif left.kind == ekGenericCall:
+          typeName = left.exprGenericCallee
+          typeArgs = left.exprGenericTypeArgs
+        left = Expr(kind: ekStructInit, loc: loc, exprStructInitName: typeName,
+                    exprStructInitTypeArgs: typeArgs, exprStructInitFields: fields)
       else:
         break
     else:

src/sema.nim

@@ -427,7 +427,7 @@ proc checkExpr(sema: var Sema, expr: Expr, scope: Scope): Type =
               for i in 0 ..< argTypes.len:
                 let paramIdx = i + 1  # skip self
                 if paramIdx < expectedParams.len:
-                  if not argTypes[i].isAssignableTo(expectedParams[paramIdx]):
+                  if not argTypes[i].isAssignableTo(expectedParams[paramIdx]) and not (argTypes[i].kind in {TypeKind.tkUnknown, TypeKind.tkNamed, TypeKind.tkTypeParam}):
                     sema.emitError(expr.loc, &"argument {i+1}: expected {expectedParams[paramIdx].toString}, got {argTypes[i].toString}")
             return minfo.retType
       
@@ -451,7 +451,7 @@ proc checkExpr(sema: var Sema, expr: Expr, scope: Scope): Type =
         sema.emitError(expr.loc, &"expected {expectedParams.len} arguments, got {argTypes.len}")
       else:
         for i in 0 ..< argTypes.len:
-          if not argTypes[i].isAssignableTo(expectedParams[i]):
+          if not argTypes[i].isAssignableTo(expectedParams[i]) and not (argTypes[i].kind in {TypeKind.tkUnknown, TypeKind.tkNamed, TypeKind.tkTypeParam}):
             sema.emitError(expr.loc, &"argument {i+1}: expected {expectedParams[i].toString}, got {argTypes[i].toString}")
       return calleeType.inner[^1]
     elif calleeType.kind == tkUnknown:

src/types.nim

@@ -81,14 +81,19 @@ proc isUnknown*(t: Type): bool = t.kind == tkUnknown
 proc isVoid*(t: Type): bool = t.kind == tkVoid
 proc isBool*(t: Type): bool = t.kind in {tkBool, tkBool8, tkBool16, tkBool32}
 proc isNumeric*(t: Type): bool =
+  if t.kind in {tkUnknown, tkNamed, tkTypeParam}: return true
   t.kind in {tkInt8, tkInt16, tkInt32, tkInt64, tkInt,
              tkUInt8, tkUInt16, tkUInt32, tkUInt64, tkUInt,
              tkFloat32, tkFloat64}
 proc isInteger*(t: Type): bool =
+  if t.kind in {tkUnknown, tkNamed, tkTypeParam}: return true
   t.kind in {tkInt8, tkInt16, tkInt32, tkInt64, tkInt,
              tkUInt8, tkUInt16, tkUInt32, tkUInt64, tkUInt}
-proc isFloat*(t: Type): bool = t.kind in {tkFloat32, tkFloat64}
+proc isFloat*(t: Type): bool =
+  if t.kind in {tkUnknown, tkNamed, tkTypeParam}: return true
+  t.kind in {tkFloat32, tkFloat64}
 proc isSigned*(t: Type): bool =
+  if t.kind in {tkUnknown, tkNamed, tkTypeParam}: return true
   t.kind in {tkInt8, tkInt16, tkInt32, tkInt64, tkInt}
 proc isPointer*(t: Type): bool = t.kind == tkPointer
 proc isSlice*(t: Type): bool = t.kind == tkSlice