diff --git a/vlib/v/ast/str.v b/vlib/v/ast/str.v
index b984a474ac..8d1ee55da6 100644
--- a/vlib/v/ast/str.v
+++ b/vlib/v/ast/str.v
@@ -4,24 +4,22 @@
 module ast
 
 // These methods are used only by vfmt, vdoc, and for debugging.
-import (
-	v.table
-	strings
-)
+import v.table
+import strings
 
 pub fn (node &FnDecl) str(t &table.Table) string {
-	mut f := strings.new_builder(30)
+	var f := strings.new_builder(30)
 	if node.is_pub {
 		f.write('pub ')
 	}
-	mut receiver := ''
+	var receiver := ''
 	if node.is_method {
-		mut styp := t.type_to_str(node.receiver.typ)
-		mut m := if node.rec_mut { 'mut ' } else { '' }
+		var styp := t.type_to_str(node.receiver.typ)
+		var m := if node.rec_mut { 'var ' } else { '' }
 		if node.rec_mut {
 			styp = styp[1..]			// remove &
 		}
-		receiver = '($node.receiver.name $m$styp) '
+		receiver = '($m$node.receiver.name $styp) '
 		/*
 		sym := t.get_type_symbol(node.receiver.typ)
 		name := sym.name.after('.')
@@ -32,7 +30,7 @@ pub fn (node &FnDecl) str(t &table.Table) string {
 		receiver = '($node.receiver.name $m$name) '
 */
 	}
-	mut name := node.name.after('.')
+	var name := node.name.after('.')
 	if node.is_c {
 		name = 'C.$name'
 	}
@@ -49,7 +47,7 @@ pub fn (node &FnDecl) str(t &table.Table) string {
 		should_add_type := is_last_arg || node.args[i + 1].typ != arg.typ || (node.is_variadic &&
 			i == node.args.len - 2)
 		f.write(arg.name)
-		mut s := t.type_to_str(arg.typ)
+		var s := t.type_to_str(arg.typ)
 		if arg.is_mut {
 			f.write(' mut')
 			if s.starts_with('&') {
@@ -163,7 +161,7 @@ pub fn (a CallArg) str() string {
 }
 
 pub fn args2str(args []CallArg) string {
-	mut res := []string
+	var res := []string
 	for a in args {
 		res << a.str()
 	}
@@ -173,7 +171,7 @@ pub fn args2str(args []CallArg) string {
 pub fn (node Stmt) str() string {
 	match node {
 		AssignStmt {
-			mut out := ''
+			var out := ''
 			for i, ident in it.left {
 				var_info := ident.var_info()
 				if var_info.is_mut {
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 1638d77465..034b2e9f65 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -138,7 +138,7 @@ pub fn (g Gen) hashes() string {
 	return res
 }
 
-pub fn (g mut Gen) init() {
+pub fn (var g Gen) init() {
 	g.cheaders.writeln('// Generated by the V compiler')
 	g.cheaders.writeln('#include <inttypes.h>')	// int64_t etc
 	g.cheaders.writeln(c_builtin_types)
@@ -163,7 +163,7 @@ pub fn (g mut Gen) init() {
 	}
 }
 
-pub fn (g mut Gen) finish() {
+pub fn (var g Gen) finish() {
 	if g.pref.build_mode != .build_module {
 		g.stringliterals.writeln('}')
 	}
@@ -171,7 +171,7 @@ pub fn (g mut Gen) finish() {
 	g.stringliterals.writeln('')
 }
 
-pub fn (g mut Gen) write_typeof_functions() {
+pub fn (var g Gen) write_typeof_functions() {
 	g.writeln('')
 	g.writeln('// >> typeof() support for sum types')
 	for typ in g.table.types {
@@ -195,7 +195,7 @@ pub fn (g mut Gen) write_typeof_functions() {
 }
 
 // V type to C type
-pub fn (g mut Gen) typ(t table.Type) string {
+pub fn (var g Gen) typ(t table.Type) string {
 	nr_muls := table.type_nr_muls(t)
 	sym := g.table.get_type_symbol(t)
 	var styp := sym.name.replace('.', '__')
@@ -228,7 +228,7 @@ pub fn (g mut Gen) typ(t table.Type) string {
 }
 
 //
-pub fn (g mut Gen) write_typedef_types() {
+pub fn (var g Gen) write_typedef_types() {
 	for typ in g.table.types {
 		match typ.kind {
 			.alias {
@@ -267,7 +267,7 @@ pub fn (g mut Gen) write_typedef_types() {
 	}
 }
 
-pub fn (g mut Gen) write_multi_return_types() {
+pub fn (var g Gen) write_multi_return_types() {
 	g.definitions.writeln('// multi return structs')
 	for typ in g.table.types {
 		// sym := g.table.get_type_symbol(typ)
@@ -288,7 +288,7 @@ pub fn (g mut Gen) write_multi_return_types() {
 	}
 }
 
-pub fn (g mut Gen) write_variadic_types() {
+pub fn (var g Gen) write_variadic_types() {
 	if g.variadic_args.size > 0 {
 		g.definitions.writeln('// variadic structs')
 	}
@@ -307,7 +307,7 @@ pub fn (g mut Gen) write_variadic_types() {
 pub fn (g Gen) save() {
 }
 
-pub fn (g mut Gen) write(s string) {
+pub fn (var g Gen) write(s string) {
 	if g.indent > 0 && g.empty_line {
 		g.out.write(tabs[g.indent])
 		// g.line_len += g.indent * 4
@@ -316,7 +316,7 @@ pub fn (g mut Gen) write(s string) {
 	g.empty_line = false
 }
 
-pub fn (g mut Gen) writeln(s string) {
+pub fn (var g Gen) writeln(s string) {
 	if g.indent > 0 && g.empty_line {
 		g.out.write(tabs[g.indent])
 	}
@@ -324,16 +324,16 @@ pub fn (g mut Gen) writeln(s string) {
 	g.empty_line = true
 }
 
-pub fn (g mut Gen) new_tmp_var() string {
+pub fn (var g Gen) new_tmp_var() string {
 	g.tmp_count++
 	return 'tmp$g.tmp_count'
 }
 
-pub fn (g mut Gen) reset_tmp_count() {
+pub fn (var g Gen) reset_tmp_count() {
 	g.tmp_count = 0
 }
 
-fn (g mut Gen) stmts(stmts []ast.Stmt) {
+fn (var g Gen) stmts(stmts []ast.Stmt) {
 	g.indent++
 	if g.inside_ternary {
 		g.write(' ( ')
@@ -350,7 +350,7 @@ fn (g mut Gen) stmts(stmts []ast.Stmt) {
 	g.indent--
 }
 
-fn (g mut Gen) stmt(node ast.Stmt) {
+fn (var g Gen) stmt(node ast.Stmt) {
 	g.stmt_start_pos = g.out.len
 	// println('cgen.stmt()')
 	// g.writeln('//// stmt start')
@@ -530,7 +530,7 @@ fn (g mut Gen) stmt(node ast.Stmt) {
 	}
 }
 
-fn (g mut Gen) write_defer_stmts() {
+fn (var g Gen) write_defer_stmts() {
 	for defer_stmt in g.defer_stmts {
 		g.writeln('// defer')
 		if defer_stmt.ifdef.len > 0 {
@@ -544,7 +544,7 @@ fn (g mut Gen) write_defer_stmts() {
 	}
 }
 
-fn (g mut Gen) for_in(it ast.ForInStmt) {
+fn (var g Gen) for_in(it ast.ForInStmt) {
 	if it.is_range {
 		// `for x in 1..10 {`
 		i := g.new_tmp_var()
@@ -624,7 +624,7 @@ fn (g mut Gen) for_in(it ast.ForInStmt) {
 }
 
 // use instead of expr() when you need to cast to sum type (can add other casts also)
-fn (g mut Gen) expr_with_cast(expr ast.Expr, got_type, exp_type table.Type) {
+fn (var g Gen) expr_with_cast(expr ast.Expr, got_type, exp_type table.Type) {
 	// cast to sum type
 	if exp_type != table.void_type {
 		exp_sym := g.table.get_type_symbol(exp_type)
@@ -646,7 +646,7 @@ fn (g mut Gen) expr_with_cast(expr ast.Expr, got_type, exp_type table.Type) {
 	g.expr(expr)
 }
 
-fn (g mut Gen) gen_assert_stmt(a ast.AssertStmt) {
+fn (var g Gen) gen_assert_stmt(a ast.AssertStmt) {
 	g.writeln('// assert')
 	g.inside_ternary = true
 	g.write('if (')
@@ -677,7 +677,7 @@ fn (g mut Gen) gen_assert_stmt(a ast.AssertStmt) {
 	g.writeln('}')
 }
 
-fn (g mut Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
+fn (var g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 	// g.write('/*assign_stmt*/')
 	if assign_stmt.is_static {
 		g.write('static ')
@@ -790,7 +790,7 @@ fn (g mut Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 	}
 }
 
-fn (g mut Gen) gen_clone_assignment(val ast.Expr, right_sym table.TypeSymbol, add_eq bool) bool {
+fn (var g Gen) gen_clone_assignment(val ast.Expr, right_sym table.TypeSymbol, add_eq bool) bool {
 	var is_ident := false
 	match val {
 		ast.Ident {
@@ -823,7 +823,7 @@ fn (g mut Gen) gen_clone_assignment(val ast.Expr, right_sym table.TypeSymbol, ad
 	return true
 }
 
-fn (g mut Gen) free_scope_vars(pos int) {
+fn (var g Gen) free_scope_vars(pos int) {
 	scope := g.file.scope.innermost(pos)
 	for _, obj in scope.objects {
 		match obj {
@@ -864,7 +864,7 @@ fn (g mut Gen) free_scope_vars(pos int) {
 	}
 }
 
-fn (g mut Gen) expr(node ast.Expr) {
+fn (var g Gen) expr(node ast.Expr) {
 	// println('cgen expr() line_nr=$node.pos.line_nr')
 	match node {
 		ast.ArrayInit {
@@ -1092,7 +1092,7 @@ fn (g mut Gen) expr(node ast.Expr) {
 	}
 }
 
-fn (g mut Gen) typeof_expr(node ast.TypeOf) {
+fn (var g Gen) typeof_expr(node ast.TypeOf) {
 	sym := g.table.get_type_symbol(node.expr_type)
 	if sym.kind == .sum_type {
 		// When encountering a .sum_type, typeof() should be done at runtime,
@@ -1110,7 +1110,7 @@ fn (g mut Gen) typeof_expr(node ast.TypeOf) {
 	}
 }
 
-fn (g mut Gen) enum_expr(node ast.Expr) {
+fn (var g Gen) enum_expr(node ast.Expr) {
 	match node {
 		ast.EnumVal {
 			g.write(it.val)
@@ -1121,7 +1121,7 @@ fn (g mut Gen) enum_expr(node ast.Expr) {
 	}
 }
 
-fn (g mut Gen) assign_expr(node ast.AssignExpr) {
+fn (var g Gen) assign_expr(node ast.AssignExpr) {
 	// g.write('/*assign_expr*/')
 	var is_call := false
 	var or_stmts := []ast.Stmt
@@ -1197,7 +1197,7 @@ fn (g mut Gen) assign_expr(node ast.AssignExpr) {
 	g.is_assign_rhs = false
 }
 
-fn (g mut Gen) infix_expr(node ast.InfixExpr) {
+fn (var g Gen) infix_expr(node ast.InfixExpr) {
 	// println('infix_expr() op="$node.op.str()" line_nr=$node.pos.line_nr')
 	// g.write('/*infix*/')
 	// if it.left_type == table.string_type_idx {
@@ -1363,7 +1363,7 @@ fn (g mut Gen) infix_expr(node ast.InfixExpr) {
 	}
 }
 
-fn (g mut Gen) match_expr(node ast.MatchExpr) {
+fn (var g Gen) match_expr(node ast.MatchExpr) {
 	// println('match expr typ=$it.expr_type')
 	// TODO
 	if node.cond_type == 0 {
@@ -1467,7 +1467,7 @@ fn (g mut Gen) match_expr(node ast.MatchExpr) {
 	g.inside_ternary = was_inside_ternary
 }
 
-fn (g mut Gen) ident(node ast.Ident) {
+fn (var g Gen) ident(node ast.Ident) {
 	if node.name == 'lld' {
 		return
 	}
@@ -1499,7 +1499,7 @@ fn (g mut Gen) ident(node ast.Ident) {
 	g.write(name)
 }
 
-fn (g mut Gen) if_expr(node ast.IfExpr) {
+fn (var g Gen) if_expr(node ast.IfExpr) {
 	// println('if_expr pos=$node.pos.line_nr')
 	// g.writeln('/* if is_expr=$node.is_expr */')
 	// If expression? Assign the value to a temp var.
@@ -1571,7 +1571,7 @@ fn (g mut Gen) if_expr(node ast.IfExpr) {
 	}
 }
 
-fn (g mut Gen) index_expr(node ast.IndexExpr) {
+fn (var g Gen) index_expr(node ast.IndexExpr) {
 	// TODO else doesn't work with sum types
 	var is_range := false
 	match node.index {
@@ -1763,7 +1763,7 @@ fn (g mut Gen) index_expr(node ast.IndexExpr) {
 	}
 }
 
-fn (g mut Gen) return_statement(node ast.Return) {
+fn (var g Gen) return_statement(node ast.Return) {
 	g.write('return')
 	if g.fn_decl.name == 'main' {
 		g.writeln(' 0;')
@@ -1841,7 +1841,7 @@ fn (g mut Gen) return_statement(node ast.Return) {
 	g.writeln(';')
 }
 
-fn (g mut Gen) const_decl(node ast.ConstDecl) {
+fn (var g Gen) const_decl(node ast.ConstDecl) {
 	for i, field in node.fields {
 		name := c_name(field.name)
 		// TODO hack. Cut the generated value and paste it into definitions.
@@ -1873,7 +1873,7 @@ fn (g mut Gen) const_decl(node ast.ConstDecl) {
 	}
 }
 
-fn (g mut Gen) const_decl_simple_define(name, val string) {
+fn (var g Gen) const_decl_simple_define(name, val string) {
 	// Simple expressions should use a #define
 	// so that we don't pollute the binary with unnecessary global vars
 	// Do not do this when building a module, otherwise the consts
@@ -1882,7 +1882,7 @@ fn (g mut Gen) const_decl_simple_define(name, val string) {
 	g.definitions.writeln(val)
 }
 
-fn (g mut Gen) struct_init(struct_init ast.StructInit) {
+fn (var g Gen) struct_init(struct_init ast.StructInit) {
 	var info := table.Struct{}
 	var is_struct := false
 	sym := g.table.get_type_symbol(struct_init.typ)
@@ -1948,7 +1948,7 @@ fn (g mut Gen) struct_init(struct_init ast.StructInit) {
 }
 
 // { user | name: 'new name' }
-fn (g mut Gen) assoc(node ast.Assoc) {
+fn (var g Gen) assoc(node ast.Assoc) {
 	g.writeln('// assoc')
 	if node.typ == 0 {
 		return
@@ -1977,7 +1977,7 @@ fn (g mut Gen) assoc(node ast.Assoc) {
 	}
 }
 
-fn (g mut Gen) generate_array_equality_fn(ptr_typ string, styp table.Type, sym &table.TypeSymbol) {
+fn (var g Gen) generate_array_equality_fn(ptr_typ string, styp table.Type, sym &table.TypeSymbol) {
 	g.array_fn_definitions << ptr_typ
 	g.definitions.writeln('bool ${ptr_typ}_arr_eq(array_${ptr_typ} a, array_${ptr_typ} b) {')
 	g.definitions.writeln('\tif (a.len != b.len) {')
@@ -2002,7 +2002,7 @@ fn verror(s string) {
 	util.verror('cgen error', s)
 }
 
-fn (g mut Gen) write_init_function() {
+fn (var g Gen) write_init_function() {
 	g.writeln('void _vinit() {')
 	g.writeln('\tbuiltin_init();')
 	g.writeln('\tvinit_string_literals();')
@@ -2028,7 +2028,7 @@ fn (g mut Gen) write_init_function() {
 	}
 }
 
-fn (g mut Gen) write_str_fn_definitions() {
+fn (var g Gen) write_str_fn_definitions() {
 	// _STR function can't be defined in vlib
 	g.writeln('
 string _STR(const char *fmt, ...) {
@@ -2069,7 +2069,7 @@ const (
 	builtins = ['string', 'array', 'KeyValue', 'DenseArray', 'map', 'Option']
 )
 
-fn (g mut Gen) write_builtin_types() {
+fn (var g Gen) write_builtin_types() {
 	var builtin_types := []table.TypeSymbol	// builtin types
 	// builtin types need to be on top
 	// everything except builtin will get sorted
@@ -2082,7 +2082,7 @@ fn (g mut Gen) write_builtin_types() {
 // C struct definitions, ordered
 // Sort the types, make sure types that are referenced by other types
 // are added before them.
-fn (g mut Gen) write_sorted_types() {
+fn (var g Gen) write_sorted_types() {
 	var types := []table.TypeSymbol	// structs that need to be sorted
 	for typ in g.table.types {
 		if !(typ.name in builtins) {
@@ -2097,7 +2097,7 @@ fn (g mut Gen) write_sorted_types() {
 	g.write_types(types_sorted)
 }
 
-fn (g mut Gen) write_types(types []table.TypeSymbol) {
+fn (var g Gen) write_types(types []table.TypeSymbol) {
 	for typ in types {
 		if typ.name.starts_with('C.') {
 			continue
@@ -2203,7 +2203,7 @@ fn (g Gen) sort_structs(typesa []table.TypeSymbol) []table.TypeSymbol {
 	return types_sorted
 }
 
-fn (g mut Gen) string_inter_literal(node ast.StringInterLiteral) {
+fn (var g Gen) string_inter_literal(node ast.StringInterLiteral) {
 	g.write('_STR("')
 	// Build the string with %
 	for i, val in node.vals {
@@ -2318,7 +2318,7 @@ fn (g mut Gen) string_inter_literal(node ast.StringInterLiteral) {
 }
 
 // `nums.filter(it % 2 == 0)`
-fn (g mut Gen) gen_filter(node ast.CallExpr) {
+fn (var g Gen) gen_filter(node ast.CallExpr) {
 	tmp := g.new_tmp_var()
 	s := g.out.after(g.stmt_start_pos)	// the already generated part of current statement
 	g.out.go_back(s.len)
@@ -2346,7 +2346,7 @@ fn (g mut Gen) gen_filter(node ast.CallExpr) {
 	g.write(tmp)
 }
 
-fn (g mut Gen) insert_before(s string) {
+fn (var g Gen) insert_before(s string) {
 	cur_line := g.out.after(g.stmt_start_pos)
 	g.out.go_back(cur_line.len)
 	g.writeln(s)
@@ -2357,7 +2357,7 @@ fn (g mut Gen) insert_before(s string) {
 // If the user is not using the optional return value. We need to pass a temp var
 // to access its fields (`.ok`, `.error` etc)
 // `os.cp(...)` => `Option bool tmp = os__cp(...); if (!tmp.ok) { ... }`
-fn (g mut Gen) or_block(var_name string, stmts []ast.Stmt, return_type table.Type) {
+fn (var g Gen) or_block(var_name string, stmts []ast.Stmt, return_type table.Type) {
 	mr_styp := g.typ(return_type)
 	mr_styp2 := mr_styp[7..]	// remove Option_
 	g.writeln(';')	// or')
@@ -2380,7 +2380,7 @@ fn (g mut Gen) or_block(var_name string, stmts []ast.Stmt, return_type table.Typ
 	g.write('}')
 }
 
-fn (g mut Gen) type_of_last_statement(stmts []ast.Stmt) (string, string) {
+fn (var g Gen) type_of_last_statement(stmts []ast.Stmt) (string, string) {
 	var last_type := ''
 	var last_expr_result_type := ''
 	if stmts.len > 0 {
@@ -2408,7 +2408,7 @@ fn (g mut Gen) type_of_last_statement(stmts []ast.Stmt) (string, string) {
 	return last_type, last_expr_result_type
 }
 
-fn (g mut Gen) type_of_call_expr(node ast.Expr) string {
+fn (var g Gen) type_of_call_expr(node ast.Expr) string {
 	match node {
 		ast.CallExpr {
 			return g.typ(it.return_type)
@@ -2421,7 +2421,7 @@ fn (g mut Gen) type_of_call_expr(node ast.Expr) string {
 }
 
 // `a in [1,2,3]` => `a == 1 || a == 2 || a == 3`
-fn (g mut Gen) in_optimization(left ast.Expr, right ast.ArrayInit) {
+fn (var g Gen) in_optimization(left ast.Expr, right ast.ArrayInit) {
 	is_str := right.elem_type == table.string_type
 	for i, array_expr in right.exprs {
 		if is_str {
@@ -2638,7 +2638,7 @@ fn (g Gen) type_default(typ table.Type) string {
 */
 }
 
-pub fn (g mut Gen) write_tests_main() {
+pub fn (var g Gen) write_tests_main() {
 	g.definitions.writeln('int g_test_oks = 0;')
 	g.definitions.writeln('int g_test_fails = 0;')
 	$if windows {
@@ -2725,7 +2725,7 @@ fn (g Gen) is_importing_os() bool {
 	return 'os' in g.table.imports
 }
 
-fn (g mut Gen) comp_if(it ast.CompIf) {
+fn (var g Gen) comp_if(it ast.CompIf) {
 	ifdef := comp_if_to_ifdef(it.val)
 	if it.is_not {
 		g.writeln('\n#ifndef ' + ifdef)
@@ -2757,7 +2757,7 @@ fn (g mut Gen) comp_if(it ast.CompIf) {
 	g.writeln('\n#endif')
 }
 
-fn (g mut Gen) go_stmt(node ast.GoStmt) {
+fn (var g Gen) go_stmt(node ast.GoStmt) {
 	tmp := g.new_tmp_var()
 	// x := node.call_expr as ast.CallEpxr // TODO
 	match node.call_expr {
@@ -2827,14 +2827,14 @@ fn (g mut Gen) go_stmt(node ast.GoStmt) {
 	}
 }
 
-fn (g mut Gen) is_expr(node ast.InfixExpr) {
+fn (var g Gen) is_expr(node ast.InfixExpr) {
 	g.expr(node.left)
 	g.write('.typ == ')
 	g.expr(node.right)
 }
 
 // already generated styp, reuse it
-fn (g mut Gen) gen_str_for_type(sym table.TypeSymbol, styp string) {
+fn (var g Gen) gen_str_for_type(sym table.TypeSymbol, styp string) {
 	if sym.has_method('str') || styp in g.str_types {
 		return
 	}
@@ -2855,7 +2855,7 @@ fn (g mut Gen) gen_str_for_type(sym table.TypeSymbol, styp string) {
 	}
 }
 
-fn (g mut Gen) gen_str_default(sym table.TypeSymbol, styp string) {
+fn (var g Gen) gen_str_default(sym table.TypeSymbol, styp string) {
 	var convertor := ''
 	var typename := ''
 	if sym.parent_idx in table.integer_type_idxs {
@@ -2885,7 +2885,7 @@ fn (g mut Gen) gen_str_default(sym table.TypeSymbol, styp string) {
 	g.definitions.writeln('}')
 }
 
-fn (g mut Gen) gen_str_for_enum(info table.Enum, styp string) {
+fn (var g Gen) gen_str_for_enum(info table.Enum, styp string) {
 	s := styp.replace('.', '__')
 	g.definitions.write('string ${s}_str($styp it) {\n\tswitch(it) {\n')
 	for i, val in info.vals {
@@ -2894,7 +2894,7 @@ fn (g mut Gen) gen_str_for_enum(info table.Enum, styp string) {
 	g.definitions.write('\t\tdefault: return tos3("unknown enum value"); } }\n')
 }
 
-fn (g mut Gen) gen_str_for_struct(info table.Struct, styp string) {
+fn (var g Gen) gen_str_for_struct(info table.Struct, styp string) {
 	// TODO: short it if possible
 	// generates all definitions of substructs
 	for i, field in info.fields {
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index f56fc01276..f1ff03f5de 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -9,7 +9,7 @@ import v.scanner
 import v.token
 import v.util
 
-pub fn (p mut Parser) call_expr(is_c, is_js bool, mod string) ast.CallExpr {
+pub fn (var p Parser) call_expr(is_c, is_js bool, mod string) ast.CallExpr {
 	first_pos := p.tok.position()
 	tok := p.tok
 	name := p.check_name()
@@ -63,7 +63,7 @@ pub fn (p mut Parser) call_expr(is_c, is_js bool, mod string) ast.CallExpr {
 	return node
 }
 
-pub fn (p mut Parser) call_args() []ast.CallArg {
+pub fn (var p Parser) call_args() []ast.CallArg {
 	var args := []ast.CallArg
 	for p.tok.kind != .rpar {
 		var is_mut := false
@@ -83,7 +83,7 @@ pub fn (p mut Parser) call_args() []ast.CallArg {
 	return args
 }
 
-fn (p mut Parser) fn_decl() ast.FnDecl {
+fn (var p Parser) fn_decl() ast.FnDecl {
 	// p.table.clear_vars()
 	pos := p.tok.position()
 	p.open_scope()
@@ -232,7 +232,7 @@ fn (p mut Parser) fn_decl() ast.FnDecl {
 	}
 }
 
-fn (p mut Parser) fn_args() ([]table.Arg, bool) {
+fn (var p Parser) fn_args() ([]table.Arg, bool) {
 	p.check(.lpar)
 	var args := []table.Arg
 	var is_variadic := false
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 01bf6b1de1..667e53ac26 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -177,26 +177,26 @@ pub fn (p &Parser) init_parse_fns() {
 	println('')
 }
 
-pub fn (p mut Parser) read_first_token() {
+pub fn (var p Parser) read_first_token() {
 	// need to call next() twice to get peek token and current token
 	p.next()
 	p.next()
 }
 
-pub fn (p mut Parser) open_scope() {
+pub fn (var p Parser) open_scope() {
 	p.scope = &ast.Scope{
 		parent: p.scope
 		start_pos: p.tok.pos
 	}
 }
 
-pub fn (p mut Parser) close_scope() {
+pub fn (var p Parser) close_scope() {
 	p.scope.end_pos = p.tok.pos
 	p.scope.parent.children << p.scope
 	p.scope = p.scope.parent
 }
 
-pub fn (p mut Parser) parse_block() []ast.Stmt {
+pub fn (var p Parser) parse_block() []ast.Stmt {
 	p.open_scope()
 	// println('parse block')
 	stmts := p.parse_block_no_scope()
@@ -205,7 +205,7 @@ pub fn (p mut Parser) parse_block() []ast.Stmt {
 	return stmts
 }
 
-pub fn (p mut Parser) parse_block_no_scope() []ast.Stmt {
+pub fn (var p Parser) parse_block_no_scope() []ast.Stmt {
 	p.check(.lcbr)
 	var stmts := []ast.Stmt
 	if p.tok.kind != .rcbr {
@@ -227,7 +227,7 @@ fn (p mut Parser) next_with_comment() {
 	p.peek_tok = p.scanner.scan()
 }
 */
-fn (p mut Parser) next() {
+fn (var p Parser) next() {
 	p.tok = p.peek_tok
 	p.peek_tok = p.scanner.scan()
 	/*
@@ -238,7 +238,7 @@ fn (p mut Parser) next() {
 */
 }
 
-fn (p mut Parser) check(expected token.Kind) {
+fn (var p Parser) check(expected token.Kind) {
 	// for p.tok.kind in [.line_comment, .mline_comment] {
 	// p.next()
 	// }
@@ -248,13 +248,13 @@ fn (p mut Parser) check(expected token.Kind) {
 	p.next()
 }
 
-fn (p mut Parser) check_name() string {
+fn (var p Parser) check_name() string {
 	name := p.tok.lit
 	p.check(.name)
 	return name
 }
 
-pub fn (p mut Parser) top_stmt() ast.Stmt {
+pub fn (var p Parser) top_stmt() ast.Stmt {
 	match p.tok.kind {
 		.key_pub {
 			match p.peek_tok.kind {
@@ -337,14 +337,14 @@ pub fn (p mut Parser) top_stmt() ast.Stmt {
 }
 
 // TODO [if vfmt]
-pub fn (p mut Parser) check_comment() ast.Comment {
+pub fn (var p Parser) check_comment() ast.Comment {
 	if p.tok.kind == .comment {
 		return p.comment()
 	}
 	return ast.Comment{}
 }
 
-pub fn (p mut Parser) comment() ast.Comment {
+pub fn (var p Parser) comment() ast.Comment {
 	pos := p.tok.position()
 	text := p.tok.lit
 	p.next()
@@ -355,7 +355,7 @@ pub fn (p mut Parser) comment() ast.Comment {
 	}
 }
 
-pub fn (p mut Parser) stmt() ast.Stmt {
+pub fn (var p Parser) stmt() ast.Stmt {
 	p.is_stmt_ident = p.tok.kind == .name
 	match p.tok.kind {
 		.lcbr {
@@ -456,7 +456,7 @@ pub fn (p mut Parser) stmt() ast.Stmt {
 }
 
 // TODO: is it possible to merge with AssignStmt?
-pub fn (p mut Parser) assign_expr(left ast.Expr) ast.AssignExpr {
+pub fn (var p Parser) assign_expr(left ast.Expr) ast.AssignExpr {
 	op := p.tok.kind
 	p.next()
 	pos := p.tok.position()
@@ -477,7 +477,7 @@ pub fn (p mut Parser) assign_expr(left ast.Expr) ast.AssignExpr {
 	return node
 }
 
-fn (p mut Parser) attribute() ast.Attr {
+fn (var p Parser) attribute() ast.Attr {
 	p.check(.lsbr)
 	if p.tok.kind == .key_if {
 		p.next()
@@ -544,7 +544,7 @@ pub fn (p &Parser) warn_with_pos(s string, pos token.Position) {
 	eprintln(ferror)
 }
 
-pub fn (p mut Parser) parse_ident(is_c, is_js bool) ast.Ident {
+pub fn (var p Parser) parse_ident(is_c, is_js bool) ast.Ident {
 	// p.warn('name ')
 	pos := p.tok.position()
 	var name := p.check_name()
@@ -569,7 +569,7 @@ pub fn (p mut Parser) parse_ident(is_c, is_js bool) ast.Ident {
 	return ident
 }
 
-fn (p mut Parser) struct_init(short_syntax bool) ast.StructInit {
+fn (var p Parser) struct_init(short_syntax bool) ast.StructInit {
 	typ := if short_syntax { table.void_type } else { p.parse_type() }
 	p.expr_mod = ''
 	// sym := p.table.get_type_symbol(typ)
@@ -615,7 +615,7 @@ fn (p mut Parser) struct_init(short_syntax bool) ast.StructInit {
 	return node
 }
 
-pub fn (p mut Parser) name_expr() ast.Expr {
+pub fn (var p Parser) name_expr() ast.Expr {
 	var node := ast.Expr{}
 	if p.inside_is {
 		p.inside_is = false
@@ -731,7 +731,7 @@ pub fn (p mut Parser) name_expr() ast.Expr {
 	return node
 }
 
-pub fn (p mut Parser) expr(precedence int) ast.Expr {
+pub fn (var p Parser) expr(precedence int) ast.Expr {
 	// println('\n\nparser.expr()')
 	var typ := table.void_type
 	var node := ast.Expr{}
@@ -897,7 +897,7 @@ pub fn (p mut Parser) expr(precedence int) ast.Expr {
 	return node
 }
 
-fn (p mut Parser) prefix_expr() ast.PrefixExpr {
+fn (var p Parser) prefix_expr() ast.PrefixExpr {
 	pos := p.tok.position()
 	op := p.tok.kind
 	if op == .amp {
@@ -913,7 +913,7 @@ fn (p mut Parser) prefix_expr() ast.PrefixExpr {
 	}
 }
 
-fn (p mut Parser) index_expr(left ast.Expr) ast.IndexExpr {
+fn (var p Parser) index_expr(left ast.Expr) ast.IndexExpr {
 	// left == `a` in `a[0]`
 	p.next()	// [
 	var has_low := true
@@ -964,13 +964,13 @@ fn (p mut Parser) index_expr(left ast.Expr) ast.IndexExpr {
 	}
 }
 
-fn (p mut Parser) filter() {
+fn (var p Parser) filter() {
 	p.scope.register('it', ast.Var{
 		name: 'it'
 	})
 }
 
-fn (p mut Parser) dot_expr(left ast.Expr) ast.Expr {
+fn (var p Parser) dot_expr(left ast.Expr) ast.Expr {
 	p.next()
 	var name_pos := p.tok.position()
 	field_name := p.check_name()
@@ -1043,7 +1043,7 @@ fn (p mut Parser) dot_expr(left ast.Expr) ast.Expr {
 	return node
 }
 
-fn (p mut Parser) infix_expr(left ast.Expr) ast.Expr {
+fn (var p Parser) infix_expr(left ast.Expr) ast.Expr {
 	op := p.tok.kind
 	// mut typ := p.
 	// println('infix op=$op.str()')
@@ -1067,7 +1067,7 @@ fn (p mut Parser) infix_expr(left ast.Expr) ast.Expr {
 
 // `.green`
 // `pref.BuildMode.default_mode`
-fn (p mut Parser) enum_val() ast.EnumVal {
+fn (var p Parser) enum_val() ast.EnumVal {
 	p.check(.dot)
 	val := p.check_name()
 	return ast.EnumVal{
@@ -1076,7 +1076,7 @@ fn (p mut Parser) enum_val() ast.EnumVal {
 	}
 }
 
-fn (p mut Parser) for_stmt() ast.Stmt {
+fn (var p Parser) for_stmt() ast.Stmt {
 	p.check(.key_for)
 	pos := p.tok.position()
 	p.open_scope()
@@ -1196,7 +1196,7 @@ fn (p mut Parser) for_stmt() ast.Stmt {
 	}
 }
 
-fn (p mut Parser) if_expr() ast.IfExpr {
+fn (var p Parser) if_expr() ast.IfExpr {
 	pos := p.tok.position()
 	var branches := []ast.IfBranch
 	var has_else := false
@@ -1267,7 +1267,7 @@ fn (p mut Parser) if_expr() ast.IfExpr {
 	}
 }
 
-fn (p mut Parser) string_expr() ast.Expr {
+fn (var p Parser) string_expr() ast.Expr {
 	is_raw := p.tok.kind == .name && p.tok.lit == 'r'
 	is_cstr := p.tok.kind == .name && p.tok.lit == 'c'
 	if is_raw || is_cstr {
@@ -1328,7 +1328,7 @@ fn (p mut Parser) string_expr() ast.Expr {
 	return node
 }
 
-fn (p mut Parser) array_init() ast.ArrayInit {
+fn (var p Parser) array_init() ast.ArrayInit {
 	first_pos := p.tok.position()
 	var last_pos := token.Position{}
 	p.check(.lsbr)
@@ -1413,7 +1413,7 @@ fn (p mut Parser) array_init() ast.ArrayInit {
 	}
 }
 
-fn (p mut Parser) map_init() ast.MapInit {
+fn (var p Parser) map_init() ast.MapInit {
 	pos := p.tok.position()
 	var keys := []ast.Expr
 	var vals := []ast.Expr
@@ -1435,7 +1435,7 @@ fn (p mut Parser) map_init() ast.MapInit {
 	}
 }
 
-fn (p mut Parser) parse_number_literal() ast.Expr {
+fn (var p Parser) parse_number_literal() ast.Expr {
 	lit := p.tok.lit
 	pos := p.tok.position()
 	var node := ast.Expr{}
@@ -1453,7 +1453,7 @@ fn (p mut Parser) parse_number_literal() ast.Expr {
 	return node
 }
 
-fn (p mut Parser) module_decl() ast.Module {
+fn (var p Parser) module_decl() ast.Module {
 	var name := 'main'
 	is_skipped := p.tok.kind != .key_module
 	if !is_skipped {
@@ -1469,7 +1469,7 @@ fn (p mut Parser) module_decl() ast.Module {
 	}
 }
 
-fn (p mut Parser) parse_import() ast.Import {
+fn (var p Parser) parse_import() ast.Import {
 	pos := p.tok.position()
 	var mod_name := p.check_name()
 	var mod_alias := mod_name
@@ -1492,7 +1492,7 @@ fn (p mut Parser) parse_import() ast.Import {
 	}
 }
 
-fn (p mut Parser) import_stmt() []ast.Import {
+fn (var p Parser) import_stmt() []ast.Import {
 	p.check(.key_import)
 	var imports := []ast.Import
 	if p.tok.kind == .lpar {
@@ -1511,7 +1511,7 @@ fn (p mut Parser) import_stmt() []ast.Import {
 	return imports
 }
 
-fn (p mut Parser) const_decl() ast.ConstDecl {
+fn (var p Parser) const_decl() ast.ConstDecl {
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
 		p.next()
@@ -1549,7 +1549,7 @@ fn (p mut Parser) const_decl() ast.ConstDecl {
 }
 
 // structs and unions
-fn (p mut Parser) struct_decl() ast.StructDecl {
+fn (var p Parser) struct_decl() ast.StructDecl {
 	first_pos := p.tok.position()
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
@@ -1705,7 +1705,7 @@ fn (p mut Parser) struct_decl() ast.StructDecl {
 	}
 }
 
-fn (p mut Parser) interface_decl() ast.InterfaceDecl {
+fn (var p Parser) interface_decl() ast.InterfaceDecl {
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
 		p.next()
@@ -1730,7 +1730,7 @@ fn (p mut Parser) interface_decl() ast.InterfaceDecl {
 	}
 }
 
-fn (p mut Parser) return_stmt() ast.Return {
+fn (var p Parser) return_stmt() ast.Return {
 	p.next()
 	// return expressions
 	var exprs := []ast.Expr
@@ -1756,7 +1756,7 @@ fn (p mut Parser) return_stmt() ast.Return {
 }
 
 // left hand side of `=` or `:=` in `a,b,c := 1,2,3`
-fn (p mut Parser) parse_assign_lhs() []ast.Ident {
+fn (var p Parser) parse_assign_lhs() []ast.Ident {
 	var idents := []ast.Ident
 	for {
 		is_mut := p.tok.kind == .key_mut || p.tok.kind == .key_var
@@ -1784,7 +1784,7 @@ fn (p mut Parser) parse_assign_lhs() []ast.Ident {
 }
 
 // right hand side of `=` or `:=` in `a,b,c := 1,2,3`
-fn (p mut Parser) parse_assign_rhs() []ast.Expr {
+fn (var p Parser) parse_assign_rhs() []ast.Expr {
 	var exprs := []ast.Expr
 	for {
 		expr := p.expr(0)
@@ -1798,7 +1798,7 @@ fn (p mut Parser) parse_assign_rhs() []ast.Expr {
 	return exprs
 }
 
-fn (p mut Parser) assign_stmt() ast.Stmt {
+fn (var p Parser) assign_stmt() ast.Stmt {
 	is_static := p.tok.kind == .key_static
 	if is_static {
 		p.next()
@@ -1841,7 +1841,7 @@ fn (p mut Parser) assign_stmt() ast.Stmt {
 	}
 }
 
-fn (p mut Parser) global_decl() ast.GlobalDecl {
+fn (var p Parser) global_decl() ast.GlobalDecl {
 	if !p.pref.translated && !p.pref.is_live && !p.builtin_mod && !p.pref.building_v && p.mod !=
 		'ui' && p.mod != 'gg2' && p.mod != 'uiold' && !os.getwd().contains('/volt') && !p.pref.enable_globals {
 		p.error('use `v --enable-globals ...` to enable globals')
@@ -1881,7 +1881,7 @@ fn (p mut Parser) global_decl() ast.GlobalDecl {
 	return glob
 }
 
-fn (p mut Parser) match_expr() ast.MatchExpr {
+fn (var p Parser) match_expr() ast.MatchExpr {
 	match_first_pos := p.tok.position()
 	p.inside_match = true
 	p.check(.key_match)
@@ -1976,7 +1976,7 @@ fn (p mut Parser) match_expr() ast.MatchExpr {
 	}
 }
 
-fn (p mut Parser) enum_decl() ast.EnumDecl {
+fn (var p Parser) enum_decl() ast.EnumDecl {
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
 		p.next()
@@ -2023,7 +2023,7 @@ fn (p mut Parser) enum_decl() ast.EnumDecl {
 	}
 }
 
-fn (p mut Parser) type_decl() ast.TypeDecl {
+fn (var p Parser) type_decl() ast.TypeDecl {
 	is_pub := p.tok.kind == .key_pub
 	if is_pub {
 		p.next()
@@ -2088,7 +2088,7 @@ fn (p mut Parser) type_decl() ast.TypeDecl {
 	}
 }
 
-fn (p mut Parser) assoc() ast.Assoc {
+fn (var p Parser) assoc() ast.Assoc {
 	var_name := p.check_name()
 	pos := p.tok.position()
 	v := p.scope.find_var(var_name) or {