diff --git a/go/_test/let.go b/go/_test/let.go
index cc099c6..dc2a6b9 100644
--- a/go/_test/let.go
+++ b/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
 			}
diff --git a/go/_test/special.vim b/go/_test/special.vim
index 855006f..134c149 100644
--- a/go/_test/special.vim
+++ b/go/_test/special.vim
@@ -11,6 +11,10 @@ function! s:ExprTokenizer.token()
   " skip ExprTokenizer.token
 endfunction
 
+function! s:StringReader.__init__()
+  " skip StringReader.__init__
+endfunction
+
 function! s:StringReader.getpos()
   " skip StringReader.getpos
 endfunction
diff --git a/go/gocompiler.vim b/go/gocompiler.vim
index 716c4cd..51e10b2 100644
--- a/go/gocompiler.vim
+++ b/go/gocompiler.vim
@@ -347,7 +347,7 @@ function s:GoCompiler.compile_function(node)
     let [_0, struct, name; _] = matchlist(left, '^\(.*\)\.\(.*\)$')
     if name == 'new'
     \ || (struct == 'ExprTokenizer' && name == 'token')
-    \ || (struct == 'StringReader' && name == 'getpos')
+    \ || (struct == 'StringReader' && (name == 'getpos' || name == '__init__'))
     \ || (struct == 'VimLParser' && (name =~ '\(push\|pop\)_context\|__init__'))
     \ || (struct == 'Compiler' && (
     \        name == '__init__'
@@ -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
diff --git a/go/type.go b/go/type.go
index cf1f17b..8971f41 100644
--- a/go/type.go
+++ b/go/type.go
@@ -167,7 +167,7 @@ func NewLvalueParser(reader *StringReader) *LvalueParser {
 
 type StringReader struct {
 	i   int
-	pos [][]interface{} // (lnum, col int)
+	pos []pos
 	buf []string
 }
 
@@ -177,10 +177,52 @@ func NewStringReader(lines []string) *StringReader {
 	return obj
 }
 
+func (self *StringReader) __init__(lines []string) {
+	size := 0
+	for _, l := range lines {
+		size += len(l) + 1 // +1 for EOL
+	}
+	self.buf = make([]string, 0, size)
+	self.pos = make([]pos, 0, size+1) // +1 for EOF
+	var lnum = 0
+	for lnum < len(lines) {
+		var col = 0
+		for _, r := range lines[lnum] {
+			c := string(r)
+			self.buf = append(self.buf, c)
+			self.pos = append(self.pos, pos{lnum: lnum + 1, col: col + 1})
+			col += len(c)
+		}
+		for lnum+1 < len(lines) && viml_eqregh(lines[lnum+1], "^\\s*\\\\") {
+			var skip = true
+			col = 0
+			for _, r := range lines[lnum+1] {
+				c := string(r)
+				if skip {
+					if c == "\\" {
+						skip = false
+					}
+				} else {
+					self.buf = append(self.buf, c)
+					self.pos = append(self.pos, pos{lnum: lnum + 2, col: col + 1})
+				}
+				col += len(c)
+			}
+			lnum += 1
+		}
+		self.buf = append(self.buf, "<EOL>")
+		self.pos = append(self.pos, pos{lnum: lnum + 1, col: col + 1})
+		lnum += 1
+	}
+	// for <EOF>
+	self.pos = append(self.pos, pos{lnum: lnum + 1, col: 0})
+	self.i = 0
+}
+
 func (self *StringReader) getpos() *pos {
-	var p = self.pos[self.i]
-	var lnum, col = p[0].(int), p[1].(int)
-	return &pos{i: self.i, lnum: lnum, col: col}
+	p := self.pos[self.i]
+	p.i = self.i
+	return &p
 }
 
 type Compiler struct {
@@ -200,7 +242,7 @@ 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 {
diff --git a/go/vimlfunc.go b/go/vimlfunc.go
index 59ebdf8..caf8f27 100644
--- a/go/vimlfunc.go
+++ b/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...)
 }
@@ -143,7 +139,7 @@ func viml_range(start, end int) []int {
 
 func viml_split(s string, sep string) []string {
 	if sep == `\zs` {
-		var ss []string
+		ss := make([]string, 0, len(s))
 		for _, r := range s {
 			ss = append(ss, string(r))
 		}
diff --git a/go/vimlfunc_test.go b/go/vimlfunc_test.go
index 9fa164d..1019761 100644
--- a/go/vimlfunc_test.go
+++ b/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
diff --git a/go/vimlparser.go b/go/vimlparser.go
index b369d30..a092aaa 100644
--- a/go/vimlparser.go
+++ b/go/vimlparser.go
@@ -427,55 +427,55 @@ func (self *VimLParser) parse_command_modifiers() {
 		var k = self.reader.read_alpha()
 		var c = self.reader.peekn(1)
 		self.reader.skip_white()
-		if viml_stridx("aboveleft", k) == 0 && viml_len(k) >= 3 {
+		if viml_stridx("aboveleft", k) == 0 && len(k) >= 3 {
 			// abo\%[veleft]
 			modifiers = append(modifiers, map[string]interface{}{"name":"aboveleft"})
-		} else if viml_stridx("belowright", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("belowright", k) == 0 && len(k) >= 3 {
 			// bel\%[owright]
 			modifiers = append(modifiers, map[string]interface{}{"name":"belowright"})
-		} else if viml_stridx("browse", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("browse", k) == 0 && len(k) >= 3 {
 			// bro\%[wse]
 			modifiers = append(modifiers, map[string]interface{}{"name":"browse"})
-		} else if viml_stridx("botright", k) == 0 && viml_len(k) >= 2 {
+		} else if viml_stridx("botright", k) == 0 && len(k) >= 2 {
 			// bo\%[tright]
 			modifiers = append(modifiers, map[string]interface{}{"name":"botright"})
-		} else if viml_stridx("confirm", k) == 0 && viml_len(k) >= 4 {
+		} else if viml_stridx("confirm", k) == 0 && len(k) >= 4 {
 			// conf\%[irm]
 			modifiers = append(modifiers, map[string]interface{}{"name":"confirm"})
-		} else if viml_stridx("keepmarks", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("keepmarks", k) == 0 && len(k) >= 3 {
 			// kee\%[pmarks]
 			modifiers = append(modifiers, map[string]interface{}{"name":"keepmarks"})
-		} else if viml_stridx("keepalt", k) == 0 && viml_len(k) >= 5 {
+		} else if viml_stridx("keepalt", k) == 0 && len(k) >= 5 {
 			// keepa\%[lt]
 			modifiers = append(modifiers, map[string]interface{}{"name":"keepalt"})
-		} else if viml_stridx("keepjumps", k) == 0 && viml_len(k) >= 5 {
+		} else if viml_stridx("keepjumps", k) == 0 && len(k) >= 5 {
 			// keepj\%[umps]
 			modifiers = append(modifiers, map[string]interface{}{"name":"keepjumps"})
-		} else if viml_stridx("keeppatterns", k) == 0 && viml_len(k) >= 5 {
+		} else if viml_stridx("keeppatterns", k) == 0 && len(k) >= 5 {
 			// keepp\%[atterns]
 			modifiers = append(modifiers, map[string]interface{}{"name":"keeppatterns"})
-		} else if viml_stridx("hide", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("hide", k) == 0 && len(k) >= 3 {
 			//hid\%[e]
 			if self.ends_excmds(c) {
 				break
 			}
 			modifiers = append(modifiers, map[string]interface{}{"name":"hide"})
-		} else if viml_stridx("lockmarks", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("lockmarks", k) == 0 && len(k) >= 3 {
 			// loc\%[kmarks]
 			modifiers = append(modifiers, map[string]interface{}{"name":"lockmarks"})
-		} else if viml_stridx("leftabove", k) == 0 && viml_len(k) >= 5 {
+		} else if viml_stridx("leftabove", k) == 0 && len(k) >= 5 {
 			// lefta\%[bove]
 			modifiers = append(modifiers, map[string]interface{}{"name":"leftabove"})
-		} else if viml_stridx("noautocmd", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("noautocmd", k) == 0 && len(k) >= 3 {
 			// noa\%[utocmd]
 			modifiers = append(modifiers, map[string]interface{}{"name":"noautocmd"})
-		} else if viml_stridx("rightbelow", k) == 0 && viml_len(k) >= 6 {
+		} else if viml_stridx("rightbelow", k) == 0 && len(k) >= 6 {
 			//rightb\%[elow]
 			modifiers = append(modifiers, map[string]interface{}{"name":"rightbelow"})
-		} else if viml_stridx("sandbox", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("sandbox", k) == 0 && len(k) >= 3 {
 			// san\%[dbox]
 			modifiers = append(modifiers, map[string]interface{}{"name":"sandbox"})
-		} else if viml_stridx("silent", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("silent", k) == 0 && len(k) >= 3 {
 			// sil\%[ent]
 			if c == "!" {
 				self.reader.get()
@@ -490,16 +490,16 @@ func (self *VimLParser) parse_command_modifiers() {
 			} else {
 				modifiers = append(modifiers, map[string]interface{}{"name":"tab"})
 			}
-		} else if viml_stridx("topleft", k) == 0 && viml_len(k) >= 2 {
+		} else if viml_stridx("topleft", k) == 0 && len(k) >= 2 {
 			// to\%[pleft]
 			modifiers = append(modifiers, map[string]interface{}{"name":"topleft"})
-		} else if viml_stridx("unsilent", k) == 0 && viml_len(k) >= 3 {
+		} else if viml_stridx("unsilent", k) == 0 && len(k) >= 3 {
 			// uns\%[ilent]
 			modifiers = append(modifiers, map[string]interface{}{"name":"unsilent"})
-		} else if viml_stridx("vertical", k) == 0 && viml_len(k) >= 4 {
+		} else if viml_stridx("vertical", k) == 0 && len(k) >= 4 {
 			// vert\%[ical]
 			modifiers = append(modifiers, map[string]interface{}{"name":"vertical"})
-		} else if viml_stridx("verbose", k) == 0 && viml_len(k) >= 4 {
+		} else if viml_stridx("verbose", k) == 0 && len(k) >= 4 {
 			// verb\%[ose]
 			if d != "" {
 				modifiers = append(modifiers, map[string]interface{}{"name":"verbose", "count":viml_str2nr(d, 10)})
@@ -803,7 +803,7 @@ func (self *VimLParser) find_command() *Cmd {
 		name = self.reader.read_alpha()
 		if name != "del" && viml_eqregh(name, "\\v^d%[elete][lp]$") {
 			self.reader.seek_set(pos)
-			name = self.reader.getn(viml_len(name) - 1)
+			name = self.reader.getn(len(name) - 1)
 		}
 	}
 	if name == "" {
@@ -814,20 +814,20 @@ func (self *VimLParser) find_command() *Cmd {
 	}
 	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
 			}
@@ -2543,7 +2543,7 @@ func (self *ExprParser) parse_expr8() *VimNode {
 					}
 				}
 			}
-			if viml_len(node.rlist) > MAX_FUNC_ARGS {
+			if len(node.rlist) > MAX_FUNC_ARGS {
 				// TODO: funcname E740: Too many arguments for function: %s
 				panic(Err("E740: Too many arguments for function", node.pos))
 			}
@@ -2723,7 +2723,7 @@ func (self *ExprParser) parse_identifier() *VimNode {
 	self.reader.skip_white()
 	var npos = self.reader.getpos()
 	var curly_parts = self.parse_curly_parts()
-	if viml_len(curly_parts) == 1 && curly_parts[0].type_ == NODE_CURLYNAMEPART {
+	if len(curly_parts) == 1 && curly_parts[0].type_ == NODE_CURLYNAMEPART {
 		var node = Node(NODE_IDENTIFIER)
 		node.pos = npos
 		node.value = curly_parts[0].value
@@ -2892,42 +2892,8 @@ func (self *LvalueParser) parse_lv9() *VimNode {
 	return node
 }
 
-func (self *StringReader) __init__(lines []string) {
-	var lnum = 0
-	for lnum < viml_len(lines) {
-		var col = 0
-		for _, c := range viml_split(lines[lnum], "\\zs") {
-			self.buf = append(self.buf, c)
-			self.pos = append(self.pos, []interface{}{lnum + 1, col + 1})
-			col += viml_len(c)
-		}
-		for lnum + 1 < viml_len(lines) && viml_eqregh(lines[lnum + 1], "^\\s*\\\\") {
-			var skip = true
-			col = 0
-			for _, c := range viml_split(lines[lnum + 1], "\\zs") {
-				if skip {
-					if c == "\\" {
-						skip = false
-					}
-				} else {
-					self.buf = append(self.buf, c)
-					self.pos = append(self.pos, []interface{}{lnum + 2, col + 1})
-				}
-				col += viml_len(c)
-			}
-			lnum += 1
-		}
-		self.buf = append(self.buf, "<EOL>")
-		self.pos = append(self.pos, []interface{}{lnum + 1, col + 1})
-		lnum += 1
-	}
-	// for <EOF>
-	self.pos = append(self.pos, []interface{}{lnum + 1, 0})
-	self.i = 0
-}
-
 func (self *StringReader) eof() bool {
-	return self.i >= viml_len(self.buf)
+	return self.i >= len(self.buf)
 }
 
 func (self *StringReader) tell() int {
@@ -2943,25 +2909,25 @@ func (self *StringReader) seek_cur(i int) {
 }
 
 func (self *StringReader) seek_end(i int) {
-	self.i = viml_len(self.buf) + i
+	self.i = len(self.buf) + i
 }
 
 func (self *StringReader) p(i int) string {
-	if self.i >= viml_len(self.buf) {
+	if self.i >= len(self.buf) {
 		return "<EOF>"
 	}
 	return self.buf[self.i + i]
 }
 
 func (self *StringReader) peek() string {
-	if self.i >= viml_len(self.buf) {
+	if self.i >= len(self.buf) {
 		return "<EOF>"
 	}
 	return self.buf[self.i]
 }
 
 func (self *StringReader) get() string {
-	if self.i >= viml_len(self.buf) {
+	if self.i >= len(self.buf) {
 		return "<EOF>"
 	}
 	self.i += 1
@@ -2978,7 +2944,7 @@ func (self *StringReader) peekn(n int) string {
 func (self *StringReader) getn(n int) string {
 	var r = ""
 	var j = 0
-	for self.i < viml_len(self.buf) && (n < 0 || j < n) {
+	for self.i < len(self.buf) && (n < 0 || j < n) {
 		var c = self.buf[self.i]
 		if c == "<EOL>" {
 			break
@@ -3003,7 +2969,7 @@ func (self *StringReader) readline() string {
 func (self *StringReader) getstr(begin *pos, end *pos) string {
 	var r = ""
 	for _, i := range viml_range(begin.i, end.i - 1) {
-		if i >= viml_len(self.buf) {
+		if i >= len(self.buf) {
 			break
 		}
 		var c = self.buf[i]
diff --git a/go/vimlparser_test.go b/go/vimlparser_test.go
index 3236c73..67f4a8a 100644
--- a/go/vimlparser_test.go
+++ b/go/vimlparser_test.go
@@ -13,7 +13,7 @@ import (
 	"testing"
 )
 
-func recovert(t *testing.T) {
+func recovert(t testing.TB) {
 	if r := recover(); r != nil {
 		t.Errorf("Recovered: %v\n%s", r, debug.Stack())
 	}
@@ -174,6 +174,16 @@ func readlines(path string) ([]string, error) {
 }
 
 func TestVimLParser_VimLParser(t *testing.T) {
+	testParseVimLParser(t)
+}
+
+func BenchmarkVimLParser_VimLParser(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		testParseVimLParser(b)
+	}
+}
+
+func testParseVimLParser(t testing.TB) {
 	defer recovert(t)
 	p, err := build.Default.Import(basePkg, "", build.FindOnly)
 	if err != nil {