feat: add range-based for loops

- Parse range expressions in expressions (0..5, 0..=5)
- Add ekRange AST node, hRange HIR node
- Lower for-range to while loop with alloca counter
- Add hBlock.isScope flag for C scope emission
- Update C backend to emit scope blocks only when isScope is set

src/c_backend.nim

@@ -307,11 +307,17 @@ proc emitStmt(be: var CBackend, node: HirNode) =
     be.emitLine("continue;")
 
   of hBlock:
+    if node.isScope:
+      be.emitLine("{")
+      inc be.indent
     for stmt in node.blockStmts:
       be.emitStmt(stmt)
     if node.blockExpr != nil:
       let val = be.emitExpr(node.blockExpr)
       be.emitLine(&"{val};")
+    if node.isScope:
+      dec be.indent
+      be.emitLine("}")
 
   of hAlloca:
     let typ = typeToC(node.allocaType)
@@ -352,12 +358,12 @@ proc emitFunc*(be: var CBackend, hfunc: HirFunc) =
   be.emitLine(&"{retType} {hfunc.name}({paramsStr}) {{")
   inc be.indent
   if hfunc.body != nil:
-    if hfunc.body.kind == hBlock and hfunc.body.blockExpr != nil and hfunc.retType.kind != tkVoid:
-      # Function returns a value via block expression — emit statements and add return
+    if hfunc.body.kind == hBlock:
       for stmt in hfunc.body.blockStmts:
         be.emitStmt(stmt)
-      let val = be.emitExpr(hfunc.body.blockExpr)
-      be.emitLine(&"return {val};")
+      if hfunc.body.blockExpr != nil and hfunc.retType.kind != tkVoid:
+        let val = be.emitExpr(hfunc.body.blockExpr)
+        be.emitLine(&"return {val};")
     else:
       be.emitStmt(hfunc.body)
   dec be.indent

src/hir.nim

@@ -34,6 +34,7 @@ type
     hBlock
     hStructInit
     hSliceInit
+    hRange
     hTupleInit
     # Match (desugared to switch/branch later)
     hMatch
@@ -106,11 +107,16 @@ type
     of hBlock:
       blockStmts*: seq[HirNode]
       blockExpr*: HirNode
+      isScope*: bool
     of hStructInit:
       structInitName*: string
       structInitFields*: seq[tuple[name: string, value: HirNode]]
     of hSliceInit:
       sliceInitElements*: seq[HirNode]
+    of hRange:
+      rangeLo*: HirNode
+      rangeHi*: HirNode
+      rangeInclusive*: bool
     of hTupleInit:
       tupleInitElements*: seq[HirNode]
     of hMatch:
@@ -162,8 +168,8 @@ proc hirCall*(callee: string, args: seq[HirNode], typ: Type, loc: SourceLocation
 proc hirReturn*(value: HirNode, loc: SourceLocation): HirNode =
   HirNode(kind: hReturn, returnValue: value, typ: makeVoid(), loc: loc)
 
-proc hirBlock*(stmts: seq[HirNode], expr: HirNode, typ: Type, loc: SourceLocation): HirNode =
-  HirNode(kind: hBlock, blockStmts: stmts, blockExpr: expr, typ: typ, loc: loc)
+proc hirBlock*(stmts: seq[HirNode], expr: HirNode, typ: Type, loc: SourceLocation, isScope: bool = false): HirNode =
+  HirNode(kind: hBlock, blockStmts: stmts, blockExpr: expr, typ: typ, loc: loc, isScope: isScope)
 
 proc hirAlloca*(name: string, typ: Type, loc: SourceLocation): HirNode =
   HirNode(kind: hAlloca, allocaType: typ, allocaName: name, typ: makePointer(typ), loc: loc)

src/hir_lower.nim

@@ -229,6 +229,9 @@ proc resolveExprType(ctx: var LowerCtx, expr: Expr): Type =
     if expr.exprSliceElements.len > 0:
       return makeSlice(ctx.resolveExprType(expr.exprSliceElements[0]))
     return makeSlice(makeUnknown())
+  of ekRange:
+    let loType = ctx.resolveExprType(expr.exprRangeLo)
+    return makeRange(loType)
   of ekTuple:
     var elems: seq[Type] = @[]
     for e in expr.exprTupleElements:
@@ -380,6 +383,12 @@ proc lowerExpr(ctx: var LowerCtx, expr: Expr): HirNode =
       elems.add(ctx.lowerExpr(e))
     return HirNode(kind: hSliceInit, sliceInitElements: elems, typ: typ, loc: loc)
 
+  of ekRange:
+    let lo = ctx.lowerExpr(expr.exprRangeLo)
+    let hi = ctx.lowerExpr(expr.exprRangeHi)
+    return HirNode(kind: hRange, rangeLo: lo, rangeHi: hi,
+                   rangeInclusive: expr.exprRangeInclusive, typ: typ, loc: loc)
+
   of ekTuple:
     var elems: seq[HirNode] = @[]
     for e in expr.exprTupleElements:
@@ -509,11 +518,53 @@ proc lowerStmt(ctx: var LowerCtx, stmt: Stmt): HirNode =
                    typ: makeVoid(), loc: loc)
 
   of skFor:
-    # Desugar: for i in iter { body } → { let __iter = iter; while __hasNext(__iter) { let i = __next(__iter); body } }
-    let iterExpr = ctx.lowerExpr(stmt.stmtForIter)
-    let body = ctx.lowerBlock(stmt.stmtForBody)
-    # Simplified: just lower the body for now
-    return HirNode(kind: hLoop, loopBody: body, typ: makeVoid(), loc: loc)
+    let iterExpr = stmt.stmtForIter
+    let body = stmt.stmtForBody
+    let varName = stmt.stmtForVar
+    let loc = stmt.loc
+    
+    # Range-based for: for i in lo..hi { body }
+    if iterExpr.kind == ekRange:
+      let lo = ctx.lowerExpr(iterExpr.exprRangeLo)
+      let hi = ctx.lowerExpr(iterExpr.exprRangeHi)
+      let inclusive = iterExpr.exprRangeInclusive
+      
+      # Determine loop variable type from range bounds
+      let varType = ctx.resolveExprType(iterExpr.exprRangeLo)
+      
+      # Create: var i = lo; while i < hi { body; i = i + 1; }
+      let initStmt = hirAlloca(varName, varType, loc)
+      let varNode = hirVar(varName, makePointer(varType), loc)
+      let initStore = hirStore(varNode, lo, loc)
+      
+      let readI = hirVar(varName, varType, loc)
+      let condOp = if inclusive: tkLe else: tkLt
+      let cond = HirNode(kind: hBinary, binaryOp: condOp,
+                         binaryLeft: readI, binaryRight: hi,
+                         typ: makeBool(), loc: loc)
+      
+      var bodyStmts: seq[HirNode] = @[]
+      bodyStmts.add(ctx.lowerBlock(body))
+      
+      let readI2 = hirVar(varName, varType, loc)
+      let one = hirLit(Token(kind: tkIntLiteral, text: "1", loc: loc), varType, loc)
+      let inc = HirNode(kind: hBinary, binaryOp: tkPlus,
+                        binaryLeft: readI2, binaryRight: one,
+                        typ: varType, loc: loc)
+      bodyStmts.add(hirStore(varNode, inc, loc))
+      
+      let whileBody = hirBlock(bodyStmts, nil, makeVoid(), loc)
+      let whileNode = HirNode(kind: hWhile, whileCond: cond, whileBody: whileBody,
+                             typ: makeVoid(), loc: loc)
+      
+      # Wrap in a block so loop variable doesn't leak into outer scope
+      let forBlock = hirBlock(@[initStmt, initStore, whileNode], nil, makeVoid(), loc, isScope = true)
+      return forBlock
+    
+    # Generic iterator for loop (simplified - just infinite loop for now)
+    let loweredIter = ctx.lowerExpr(iterExpr)
+    let loweredBody = ctx.lowerBlock(body)
+    return HirNode(kind: hLoop, loopBody: loweredBody, typ: makeVoid(), loc: loc)
 
   of skDoWhile:
     let body = ctx.lowerBlock(stmt.stmtDoWhileBody)

src/parser.nim

@@ -326,6 +326,7 @@ proc parseAdd(p: var Parser): Expr
 proc parseShift(p: var Parser): Expr
 proc parseCast(p: var Parser): Expr
 proc parseComparison(p: var Parser): Expr
+proc parseRange(p: var Parser): Expr
 proc parseEquality(p: var Parser): Expr
 proc parseBitAnd(p: var Parser): Expr
 proc parseBitXor(p: var Parser): Expr
@@ -583,12 +584,22 @@ proc parseComparison(p: var Parser): Expr =
     left = newBinaryExpr(op, left, right, loc)
   return left
 
-proc parseEquality(p: var Parser): Expr =
+proc parseRange(p: var Parser): Expr =
   let loc = p.currentLoc
   var left = p.parseComparison()
+  if p.check(tkDotDot) or p.check(tkDotDotEqual):
+    let inclusive = p.check(tkDotDotEqual)
+    discard p.advance()
+    let right = p.parseComparison()
+    return Expr(kind: ekRange, loc: loc, exprRangeLo: left, exprRangeHi: right, exprRangeInclusive: inclusive)
+  return left
+
+proc parseEquality(p: var Parser): Expr =
+  let loc = p.currentLoc
+  var left = p.parseRange()
   while p.checkAny([tkEq, tkNe]):
     let op = p.advance().kind
-    let right = p.parseComparison()
+    let right = p.parseRange()
     left = newBinaryExpr(op, left, right, loc)
   return left