From 8cb7965aa592615afb50a9395390fae51b890712 Mon Sep 17 00:00:00 2001
From: gingerBill <gingerBill@users.noreply.github.com>
Date: Wed, 11 Feb 2026 15:33:14 +0000
Subject: `for init; x in y {}` style loops

---
 src/parser.cpp | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

(limited to 'src/parser.cpp')

diff --git a/src/parser.cpp b/src/parser.cpp
index 159eb65f8..42c69cd4c 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -353,12 +353,14 @@ gb_internal Ast *clone_ast(Ast *node, AstFile *f) {
 		break;
 	case Ast_RangeStmt:
 		n->RangeStmt.label = clone_ast(n->RangeStmt.label, f);
+		n->RangeStmt.init  = clone_ast(n->RangeStmt.init, f);
 		n->RangeStmt.vals  = clone_ast_array(n->RangeStmt.vals, f);
 		n->RangeStmt.expr  = clone_ast(n->RangeStmt.expr, f);
 		n->RangeStmt.body  = clone_ast(n->RangeStmt.body, f);
 		break;
 	case Ast_UnrollRangeStmt:
 		n->UnrollRangeStmt.args = clone_ast_array(n->UnrollRangeStmt.args, f);
+		n->UnrollRangeStmt.init = clone_ast(n->UnrollRangeStmt.init, f);
 		n->UnrollRangeStmt.val0 = clone_ast(n->UnrollRangeStmt.val0, f);
 		n->UnrollRangeStmt.val1 = clone_ast(n->UnrollRangeStmt.val1, f);
 		n->UnrollRangeStmt.expr = clone_ast(n->UnrollRangeStmt.expr, f);
@@ -1055,9 +1057,10 @@ gb_internal Ast *ast_for_stmt(AstFile *f, Token token, Ast *init, Ast *cond, Ast
 	return result;
 }
 
-gb_internal Ast *ast_range_stmt(AstFile *f, Token token, Slice<Ast *> vals, Token in_token, Ast *expr, Ast *body) {
+gb_internal Ast *ast_range_stmt(AstFile *f, Token token, Ast *init, Slice<Ast *> vals, Token in_token, Ast *expr, Ast *body) {
 	Ast *result = alloc_ast_node(f, Ast_RangeStmt);
 	result->RangeStmt.token = token;
+	result->RangeStmt.init = init;
 	result->RangeStmt.vals = vals;
 	result->RangeStmt.in_token = in_token;
 	result->RangeStmt.expr  = expr;
@@ -1065,9 +1068,10 @@ gb_internal Ast *ast_range_stmt(AstFile *f, Token token, Slice<Ast *> vals, Toke
 	return result;
 }
 
-gb_internal Ast *ast_unroll_range_stmt(AstFile *f, Token unroll_token, Slice<Ast *> args, Token for_token, Ast *val0, Ast *val1, Token in_token, Ast *expr, Ast *body) {
+gb_internal Ast *ast_unroll_range_stmt(AstFile *f, Token unroll_token, Ast *init, Slice<Ast *> args, Token for_token, Ast *val0, Ast *val1, Token in_token, Ast *expr, Ast *body) {
 	Ast *result = alloc_ast_node(f, Ast_UnrollRangeStmt);
 	result->UnrollRangeStmt.unroll_token = unroll_token;
+	result->UnrollRangeStmt.init      = init;
 	result->UnrollRangeStmt.args      = args;
 	result->UnrollRangeStmt.for_token = for_token;
 	result->UnrollRangeStmt.val0      = val0;
@@ -4883,7 +4887,7 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 				body = parse_block_stmt(f, false);
 			}
 
-			return ast_range_stmt(f, token, {}, in_token, rhs, body);
+			return ast_range_stmt(f, token, init, {}, in_token, rhs, body);
 		}
 
 		if (f->curr_token.kind != Token_Semicolon) {
@@ -4898,9 +4902,20 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 			cond = nullptr;
 
 			if (f->curr_token.kind == Token_OpenBrace || f->curr_token.kind == Token_do) {
-				syntax_error(f->curr_token, "Expected ';', followed by a condition expression and post statement, got %.*s", LIT(token_strings[f->curr_token.kind]));
+				syntax_error(f->curr_token, "Expected ';', followed by a condition expression and post statement, or 'x in y' style loop, got %.*s", LIT(token_strings[f->curr_token.kind]));
 			} else {
 				if (f->curr_token.kind != Token_Semicolon) {
+					if (f->curr_token.kind == Token_Ident) {
+						// for init; x in y { }
+						Token next_token = peek_token(f);
+						if (next_token.kind == Token_in || next_token.kind == Token_Comma) {
+							cond = parse_simple_stmt(f, StmtAllowFlag_In);
+							GB_ASSERT(cond->kind == Ast_AssignStmt && cond->AssignStmt.op.kind == Token_in);
+							is_range = true;
+							goto range_skip;
+						}
+					}
+
 					cond = parse_simple_stmt(f, StmtAllowFlag_None);
 				}
 
@@ -4918,6 +4933,7 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 		}
 	}
 
+range_skip:;
 
 	if (allow_token(f, Token_do)) {
 		body = parse_do_body(f, token, "the for statement");
@@ -4933,7 +4949,7 @@ gb_internal Ast *parse_for_stmt(AstFile *f) {
 		if (cond->AssignStmt.rhs.count > 0) {
 			rhs = cond->AssignStmt.rhs[0];
 		}
-		return ast_range_stmt(f, token, vals, in_token, rhs, body);
+		return ast_range_stmt(f, token, init, vals, in_token, rhs, body);
 	}
 
 	cond = convert_stmt_to_expr(f, cond, str_lit("boolean expression"));
@@ -5267,6 +5283,7 @@ gb_internal Ast *parse_unrolled_for_loop(AstFile *f, Token unroll_token) {
 	}
 
 	Token for_token = expect_token(f, Token_for);
+	Ast *init = nullptr;
 	Ast *val0 = nullptr;
 	Ast *val1 = nullptr;
 	Token in_token = {};
@@ -5309,7 +5326,7 @@ gb_internal Ast *parse_unrolled_for_loop(AstFile *f, Token unroll_token) {
 	if (bad_stmt) {
 		return ast_bad_stmt(f, unroll_token, f->curr_token);
 	}
-	return ast_unroll_range_stmt(f, unroll_token, slice_from_array(args), for_token, val0, val1, in_token, expr, body);
+	return ast_unroll_range_stmt(f, unroll_token, init, slice_from_array(args), for_token, val0, val1, in_token, expr, body);
 }
 
 gb_internal Ast *parse_stmt(AstFile *f) {
-- 
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