use builtin len instead of viml_len to avoid allocations

benchmark                            old ns/op     new ns/op     delta
BenchmarkVimLParser_VimLParser-4     522557385     384606362     -26.40%

go/_test/let.go

@@ -32,20 +32,20 @@ if x {
 func F() {
 	var cmd *Cmd = nil
 	for _, x := range builtin_commands {
-		if viml_stridx(x.name, name) == 0 && viml_len(name) >= x.minlen {
+		if viml_stridx(x.name, name) == 0 && len(name) >= x.minlen {
 			cmd = x
 			break
 		}
 	}
 	if self.neovim {
 		for _, x := range neovim_additional_commands {
-			if viml_stridx(x.name, name) == 0 && viml_len(name) >= x.minlen {
+			if viml_stridx(x.name, name) == 0 && len(name) >= x.minlen {
 				cmd = x
 				break
 			}
 		}
 		for _, x := range neovim_removed_commands {
-			if viml_stridx(x.name, name) == 0 && viml_len(name) >= x.minlen {
+			if viml_stridx(x.name, name) == 0 && len(name) >= x.minlen {
 				cmd = nil
 				break
 			}

go/gocompiler.vim

@@ -871,6 +871,8 @@ function s:GoCompiler.compile_call(node)
   if index(s:viml_builtin_functions, left) != -1
     if left == 'add'
       let left = 'append'
+    elseif left == 'len'
+      let left = 'len'
     else
       let left = printf('viml_%s', left)
     endif

go/type.go

@@ -200,7 +200,7 @@ func (self *Compiler) __init__() {
 }
 
 func (self *Compiler) out(f string, args ...interface{}) {
-	if viml_len(args) == 0 {
+	if len(args) == 0 {
 		if string(f[0]) == ")" {
 			self.lines[len(self.lines)-1] += f
 		} else {

go/vimlfunc.go

@@ -77,7 +77,7 @@ func init() {
 type vimlList interface{}
 
 func viml_empty(obj interface{}) bool {
-	return viml_len(obj) == 0
+	return reflect.ValueOf(obj).Len() == 0
 }
 
 func viml_equalci(a, b string) bool {
@@ -125,10 +125,6 @@ func viml_join(lst vimlList, sep string) string {
 	return strings.Join(ss, sep)
 }
 
-func viml_len(obj interface{}) int {
-	return reflect.ValueOf(obj).Len()
-}
-
 func viml_printf(f string, args ...interface{}) string {
 	return fmt.Sprintf(f, args...)
 }

go/vimlfunc_test.go

@@ -5,26 +5,6 @@ import (
 	"testing"
 )
 
-func TestViml_len(t *testing.T) {
-	tests := []struct {
-		in   interface{}
-		want int
-	}{
-		{in: "hoge", want: 4},
-		{in: "あいうえお", want: 15},
-		{in: "", want: 0},
-		{in: []string{"hoge", "foo"}, want: 2},
-		{in: []int{1, 2, 3}, want: 3},
-		{in: []interface{}{1, "2", float64(3)}, want: 3},
-	}
-	for _, tt := range tests {
-		got := viml_len(tt.in)
-		if got != tt.want {
-			t.Errorf("viml_len(%v) = %v, want %v", tt.in, got, tt.want)
-		}
-	}
-}
-
 func TestViml_eqreg(t *testing.T) {
 	tests := []struct {
 		in   string