diff --git a/compiler/comptime.v b/compiler/comptime.v
index 28d10ae618..6b7bb7ee3c 100644
--- a/compiler/comptime.v
+++ b/compiler/comptime.v
@@ -236,3 +236,30 @@ fn (p mut Parser) comptime_method_call(typ Type) {
 	} 
 } 
 
+fn (p mut Parser) gen_array_str(typ mut Type) {
+	typ.add_method(Fn{
+		name: 'str',
+		typ: 'string'
+		args: [Var{typ: typ.name, is_arg:true}] 
+		is_method: true 
+		receiver_typ: typ.name 
+	}) 
+	t := typ.name 
+	elm_type := t.right(6) 
+	p.cgen.fns << '
+string ${t}_str($t a) {
+	strings__Builder sb = strings__new_builder(a.len * 3); 
+	strings__Builder_write(&sb, tos2("[")) ; 
+	for (int i = 0; i < a.len; i++) {
+		strings__Builder_write(&sb, ${elm_type}_str( (($elm_type *) a.data)[i])); 
+
+	if (i < a.len - 1) {
+		strings__Builder_write(&sb, tos2(", ")) ; 
+		 
+	} 
+} 
+strings__Builder_write(&sb, tos2("]")) ; 
+return strings__Builder_str(sb); 
+} ' 
+} 
+
diff --git a/compiler/fn.v b/compiler/fn.v
index 0930b16920..8374050b7a 100644
--- a/compiler/fn.v
+++ b/compiler/fn.v
@@ -794,8 +794,15 @@ fn (p mut Parser) fn_call_args(f mut Fn) *Fn {
 		// If `arg` is mutable, the caller needs to provide `mut`: 
 		// `mut numbers := [1,2,3]; reverse(mut numbers);`
 		if arg.is_mut {
-			if p.tok != .key_mut {
-				p.error('`$arg.name` is a mutable argument, you need to provide `mut`: `$f.name(...mut a...)`')
+			if p.tok != .key_mut && p.tok == .name {
+				mut dots_example :=  'mut $p.lit' 
+				if i > 0 {
+					dots_example = '.., ' + dots_example 
+				} 
+				if i < f.args.len - 1 {
+					dots_example = dots_example + ',..' 
+				} 
+				p.error('`$arg.name` is a mutable argument, you need to provide `mut`: `$f.name($dots_example)`')	
 			}
 			if p.peek() != .name {
 				p.error('`$arg.name` is a mutable argument, you need to provide a variable to modify: `$f.name(... mut a...)`')
@@ -831,6 +838,13 @@ fn (p mut Parser) fn_call_args(f mut Fn) *Fn {
 			}
 			// Make sure this type has a `str()` method
 			if !T.has_method('str') {
+				// Arrays have automatic `str()` methods 
+				if T.name.starts_with('array_') {
+					p.gen_array_str(mut T) 
+					p.cgen.set_placeholder(ph, '${typ}_str(')
+					p.gen(')')
+					continue 
+				} 
 				error_msg := ('`$typ` needs to have method `str() string` to be printable')
 				if T.fields.len > 0 {
 					mut index := p.cgen.cur_line.len - 1
diff --git a/compiler/parser.v b/compiler/parser.v
index 2005fe9a6b..99696e0958 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -793,7 +793,7 @@ fn (p mut Parser) error(s string) {
 	p.cgen.save()
 	// V git pull hint
 	cur_path := os.getwd()
-	if !p.pref.is_repl && ( p.file_path.contains('v/compiler') || cur_path.contains('v/compiler') ){
+	if !p.pref.is_repl && !p.pref.is_test && ( p.file_path.contains('v/compiler') || cur_path.contains('v/compiler') ){
 		println('\n=========================')
 		println('It looks like you are building V. It is being frequently updated every day.') 
 		println('If you didn\'t modify the compiler\'s code, most likely there was a change that ')
@@ -1102,7 +1102,7 @@ fn (p mut Parser) vh_genln(s string) {
 }
 
 fn (p mut Parser) statement(add_semi bool) string {
-	if(p.returns) {
+	if p.returns { //&& !p.is_vweb {
 		p.error('unreachable code')
 	}
 	p.cgen.is_tmp = false
@@ -1780,7 +1780,12 @@ fn (p mut Parser) dot(str_typ string, method_ph int) string {
 		//println('dot() field_name=$field_name typ=$str_typ prev_tok=${prev_tok.str()}') 
 	//}
 	has_field := p.table.type_has_field(typ, field_name)
-	has_method := p.table.type_has_method(typ, field_name)
+	mut has_method := p.table.type_has_method(typ, field_name)
+	// generate `.str()` 
+	if !has_method && field_name == 'str' && typ.name.starts_with('array_') { 
+		p.gen_array_str(mut typ) 
+		has_method = true 
+	} 
 	if !typ.is_c && !has_field && !has_method && !p.first_pass() {
 		if typ.name.starts_with('Option_') {
 			opt_type := typ.name.right(7) 
diff --git a/compiler/query.v b/compiler/query.v
index 3189329d7d..402adfd77a 100644
--- a/compiler/query.v
+++ b/compiler/query.v
@@ -1,3 +1,7 @@
+// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
 module main 
 
 import strings 
@@ -29,7 +33,7 @@ fn (p mut Parser) select_query(fn_ph int) string {
 	} 
 	for field in typ.fields {
 		//println('registering sql field var $field.name') 
-		p.cur_fn.register_var({ field | is_used:true}) 
+		p.cur_fn.register_var({ field | is_used:true })  
 	} 
 	q += table_name 
 	// `where` statement 
diff --git a/compiler/table.v b/compiler/table.v
index 1873d27850..5294ddd89a 100644
--- a/compiler/table.v
+++ b/compiler/table.v
@@ -60,6 +60,7 @@ mut:
 	// It allows having things like `fn (f Foo) bar()` before `Foo` is defined.
 	// This information is needed in the first pass.
 	is_placeholder bool
+	gen_str	       bool  // needs `.str()` method generation 
 }
 
 // For debugging types
@@ -434,7 +435,7 @@ fn (t mut Type) add_gen_type(type_name string) {
 }
 */ 
 
-fn (p &Parser) find_type(name string) *Type {
+fn (p &Parser) find_type(name string) &Type {
 	typ := p.table.find_type(name)
 	if typ.name.len == 0 {
 		return p.table.find_type(p.prepend_mod(name))
diff --git a/compiler/tests/mut_test.v b/compiler/tests/mut_test.v
index 509de43e68..a8d7cf002d 100644
--- a/compiler/tests/mut_test.v
+++ b/compiler/tests/mut_test.v
@@ -1,14 +1,14 @@
-fn foo(a mut []int) {
+fn foo(b int, a mut []int) {
 	a[0] = 7 
 	a << 4 
 } 
 
 // TODO 
 fn test_mut() {
-	mut a := [1,2,3] 
-	foo(mut a) 
+	mut numbers := [1,2,3] 
+	foo(7, numbers) 
 	//assert a.len == 4 
-	assert a[0] == 7 
+	assert numbers[0] == 7 
 	//assert a[3] == 4 
 
 	n := 1 
diff --git a/compiler/tests/str_gen_test.v b/compiler/tests/str_gen_test.v
new file mode 100644
index 0000000000..97230724d5
--- /dev/null
+++ b/compiler/tests/str_gen_test.v
@@ -0,0 +1,16 @@
+struct Foo {
+	a int 
+} 
+
+fn test_array_str() {
+	f := Foo{34}
+	println(f) 
+	//s := f.str() 
+	//println(s) 
+	n := [i64(1), 2, 3] 
+	assert n.str() == '[1, 2, 3]' 
+	println(n)  // make sure the array is printable 
+	n2 := [4,5,6] 
+	assert n2.str() == '[4, 5, 6]' 
+	println(n2) 
+} 
diff --git a/examples/vweb/test_app.v b/examples/vweb/test_app.v
index e0e6ae73bd..65599620e7 100644
--- a/examples/vweb/test_app.v
+++ b/examples/vweb/test_app.v
@@ -23,7 +23,13 @@ pub fn (app mut App) json_endpoint() {
         app.vweb.json('{"a": 3}')
 }
 
+/* 
 pub fn (app mut App) index() {
+	$vweb.html() 
+}
+*/ 
+
+pub fn (app mut App) text() {
         app.vweb.text('hello world')
 }
 
diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 4d4449ec35..5c7d38ff54 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -4,6 +4,8 @@
 
 module builtin
 
+import strings 
+
 struct array {
 pub:
 	// Using a void pointer allows to implement arrays without generics and without generating
@@ -206,31 +208,6 @@ pub fn (a array) reverse() array {
 	return arr
 }
 
-pub fn (a []int) str() string {
-	mut res := '['
-	for i := 0; i < a.len; i++ {
-		val := a[i]
-		res += '$val'
-		if i < a.len - 1 {
-			res += ', '
-		}
-	}
-	res += ']'
-	return res
-}
-
-pub fn (a []u64) str() string {
-	mut res := '['
-	for i := 0; i < a.len; i++ {
-		val := a[i]
-		res += '$val'
-		if i < a.len - 1 {
-			res += ', '
-		}
-	}
-	res += ']'
-	return res
-}
 //pub fn (a []int) free() {
 pub fn (a array) free() {
 	//if a.is_slice {
@@ -239,19 +216,19 @@ pub fn (a array) free() {
 	C.free(a.data)
 }
 
-// TODO generic
 // "[ 'a', 'b', 'c' ]"
 pub fn (a []string) str() string {
-	mut res := '['
+	mut sb := strings.new_builder(a.len * 3) 
+	sb.write('[') 
 	for i := 0; i < a.len; i++ {
 		val := a[i]
-		res += '"$val"'
+		sb.write('"$val"') 
 		if i < a.len - 1 {
-			res += ', '
+			sb.write(', ') 
 		}
 	}
-	res += ']'
-	return res
+	sb.write(']') 
+	return sb.str() 
 }
 
 pub fn (b []byte) hex() string {