diff --git a/src/codegen/codegen.ibu b/src/codegen/codegen.ibu
index 153d3d9..a1f47a4 100644
--- a/src/codegen/codegen.ibu
+++ b/src/codegen/codegen.ibu
@@ -4,18 +4,7 @@
 #include "linux-syscall/header.ibu"
 
 func gen_expr(g *Gen, node *Node) i32;
-func gen_lhs_rhs(g *Gen, lhs *Node, rhs *Node) i32;
-func gen_addr(g *Gen, node *Node) i32;
-func gen_store(ty *Type) i32;
-func gen_load(g *Gen, ty *Type) i32;
-func gen_condition_store(ty *Type) i32;
-func func_call_args_to_stack(g *Gen, args *Vec, ty *Type) i32;
 func gen_stmt(g *Gen, node *Node) i32;
-func gen_node_block(g *Gen, stmts *Vec) i32;
-func gen_stmt(g *Gen, node *Node) i32;
-func assign_func_params_offset(g *Gen, obj *Object) i32;
-func assign_local_var_offset(g *Gen, obj *Object) i32;
-func has_main(object *Object) bool;
 
 func new_gen() *Gen {
     let g *Gen = alloc(typesize(Gen));
diff --git a/src/parser/header.ibu b/src/parser/header.ibu
index 4065a72..d0c8f5b 100644
--- a/src/parser/header.ibu
+++ b/src/parser/header.ibu
@@ -86,9 +86,9 @@ struct Type {
 	tok *Token,
 }
 
-func unexpected_token_error(expected *u8, tok *Token, msg *u8) i32;
-func unkown_type_error(types *Vec, tok *Token, msg *u8) i32;
-func unkown_member_error(members *Vec, tok *Token, msg *u8) i32;
+func unexpected_token_error(expected *u8, tok *Token, msg *u8) u0;
+func unkown_type_error(types *Vec, tok *Token, msg *u8) u0;
+func unkown_member_error(members *Vec, tok *Token, msg *u8) u0;
 #define ObjectKind	i32
 #define OBJ_FUNC	0
 #define OBJ_VAR		1
diff --git a/src/parser/parser.ibu b/src/parser/parser.ibu
index 54984cf..4e0a9d8 100644
--- a/src/parser/parser.ibu
+++ b/src/parser/parser.ibu
@@ -9,13 +9,13 @@ func parse_expr(p *Parser) *Node;
 func parse_stmt(p *Parser) *Node;
 func cmp_type(ty1 *Type, ty2 *Type) bool;
 
-func unexpected_token_error(expected *u8, tok *Token, msg *u8) i32 {
+func unexpected_token_error(expected *u8, tok *Token, msg *u8) u0 {
 	print_error_with_code(tok, msg);
 	eprintf("help: expected `%s` but got `%s`\n", expected, tok.lit);
 	exit(1);
 }
 
-func unkown_type_error(types *Vec, tok *Token, msg *u8) i32{
+func unkown_type_error(types *Vec, tok *Token, msg *u8) u0 {
 	print_error_with_code(tok, msg);
 
 	if types.len == 0 {
@@ -42,7 +42,7 @@ func unkown_type_error(types *Vec, tok *Token, msg *u8) i32{
 	exit(1);
 }
 
-func unkown_member_error(members *Vec, tok *Token, msg *u8) i32 {
+func unkown_member_error(members *Vec, tok *Token, msg *u8) u0 {
 	print_error_with_code(tok, msg);
 
 	if members.len == 0 {
diff --git a/src/tokenizer/header.ibu b/src/tokenizer/header.ibu
index cd1c1bf..886ae80 100644
--- a/src/tokenizer/header.ibu
+++ b/src/tokenizer/header.ibu
@@ -31,8 +31,8 @@ struct Tokenizer {
 }
 
 func copy_token(source *Token, dest *Token) u0;
-func print_error_with_code(tok *Token, msg *u8) i32;
-func print_error(tok *Token, msg *u8) i32;
+func print_error_with_code(tok *Token, msg *u8) u0;
+func print_error(tok *Token, msg *u8) u0;
 func new_tokenizer(file_name *u8, program *u8) *Tokenizer;
 func tokenize(t *Tokenizer) *Token;
 
diff --git a/src/tokenizer/tokenizer.ibu b/src/tokenizer/tokenizer.ibu
index da3c3d5..da6e2b1 100644
--- a/src/tokenizer/tokenizer.ibu
+++ b/src/tokenizer/tokenizer.ibu
@@ -21,7 +21,7 @@ func frepeat_str(fd i32, str *u8, n i32) i32 {
 	return 0;
 }
 
-func print_error_with_code(tok *Token, msg *u8) i32 {
+func print_error_with_code(tok *Token, msg *u8) u0 {
 	eprintf("\033[1m\033[31m--> %s:%d:%d: error:\033[0m\n", tok.file_name, tok.line, tok.col);
 
 	eprintf(" | \n");
@@ -50,7 +50,7 @@ func print_error_with_code(tok *Token, msg *u8) i32 {
 	return 0;
 }
 
-func print_error(tok *Token, msg *u8) i32 {
+func print_error(tok *Token, msg *u8) u0 {
 	print_error_with_code(tok, msg);
 	exit(1);
 }
@@ -89,8 +89,8 @@ func starts_with(a *u8, b *u8) bool {
 	return true;
 }
 
-func tokenizer_next(t *Tokenizer) i32 {
-	if *t.program == '\n' { // new line
+func tokenizer_next(t *Tokenizer) u0 {
+	if *t.program == '\n' {
 		t.line++;
 		t.col = 0;
 		t.program++;
@@ -99,16 +99,14 @@ func tokenizer_next(t *Tokenizer) i32 {
 		t.col++;
 		t.program++;
 	}
-	return 0;
 }
 
-func tokenizer_next_n(t *Tokenizer, n i32) i32 {
+func tokenizer_next_n(t *Tokenizer, n i32) u0 {
     let idx i32 = 0;
 	while idx < n {
 		tokenizer_next(t);
 		idx++;
 	}
-	return 0;
 }
 
 func new_token(t *Tokenizer, kind TokenKind) *Token {
@@ -142,13 +140,12 @@ func tokenize_punct(t *Tokenizer) *Token {
 	return nil;
 }
 
-func skip_single_line_comment(t *Tokenizer) i32 {
+func skip_single_line_comment(t *Tokenizer) u0 {
 	if starts_with(t.program, "//") {
 		while (*t.program != '\n') && (*t.program != '\0') {
 			tokenizer_next(t);
 		}
 	}
-	return 0;
 }
 
 func string_end(t *Tokenizer, str *u8) *u8 {
@@ -179,8 +176,8 @@ func from_hex(c u8) u8 {
 	return c - 'A' + 10;
 }
 
-func read_escaped_char(t *Tokenizer) i32 {
-    let c i32;
+func read_escaped_char(t *Tokenizer) u8 {
+    let c u8;
 	tokenizer_next(t);
 	if '0' <= *t.program <= '7' {
 		c = *t.program - '0';
@@ -252,9 +249,9 @@ func tokenize_number(t *Tokenizer) *Token {
 func tokenize_char(t *Tokenizer) *Token {
     let tok *Token = new_token(t, TK_NUM);
     let char_start *u8 = t.program;
-	tokenizer_next(t); // skip start '\''
+	tokenizer_next(t);
 
-    let c i32;
+    let c u8;
 	if *t.program == '\\' {
 		c = read_escaped_char(t);
 	} else {