diff --git a/complete.go b/complete.go
index 4655946..262722b 100644
--- a/complete.go
+++ b/complete.go
@@ -6,6 +6,10 @@ import (
 	"io"
 )
 
+type AutoCompleter interface {
+	Do(line []rune, pos int) (newLine [][]rune, offset int)
+}
+
 type opCompleter struct {
 	w  io.Writer
 	op *Operation
diff --git a/complete_helper.go b/complete_helper.go
new file mode 100644
index 0000000..82926dd
--- /dev/null
+++ b/complete_helper.go
@@ -0,0 +1,61 @@
+package readline
+
+type PrefixCompleter struct {
+	Name     []rune
+	Children []*PrefixCompleter
+}
+
+func NewPrefixCompleter(pc ...*PrefixCompleter) *PrefixCompleter {
+	return PcItem("", pc...)
+}
+
+func PcItem(name string, pc ...*PrefixCompleter) *PrefixCompleter {
+	if len(pc) != 0 {
+		name += " "
+	}
+	return &PrefixCompleter{
+		Name:     []rune(name),
+		Children: pc,
+	}
+}
+
+func (p *PrefixCompleter) Do(line []rune, pos int) (newLine [][]rune, offset int) {
+	line = line[:pos]
+	goNext := false
+	var lineCompleter *PrefixCompleter
+	for _, child := range p.Children {
+		if len(line) >= len(child.Name) {
+			if RunesHasPrefix(line, child.Name) {
+				newLine = append(newLine, child.Name)
+				offset = len(child.Name)
+				lineCompleter = child
+				goNext = true
+			}
+		} else {
+			if RunesHasPrefix(child.Name, line) {
+				newLine = append(newLine, child.Name[len(line):])
+				offset = len(line)
+				lineCompleter = child
+			}
+		}
+	}
+
+	if len(newLine) != 1 {
+		return
+	}
+
+	tmpLine := make([]rune, 0, len(line))
+	for i := offset; i < len(line); i++ {
+		if line[offset] == ' ' {
+			continue
+		}
+
+		tmpLine = append(tmpLine, line[i:]...)
+		return lineCompleter.Do(tmpLine, len(tmpLine))
+	}
+
+	if goNext {
+		return lineCompleter.Do(nil, 0)
+	}
+	return
+}
diff --git a/example/main.go b/example/main.go
index c9199e6..8875e14 100644
--- a/example/main.go
+++ b/example/main.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"fmt"
 	"io"
 	"log"
 	"strconv"
@@ -18,30 +17,25 @@ bye: quit
 `[1:])
 }
 
-type Completer struct {
-}
-
-func (c *Completer) Do(line []rune, pos int) (newLine [][]rune, off int) {
-	list := [][]rune{
-		[]rune("sayhello"), []rune("help"), []rune("bye"),
-	}
-	for i := 0; i <= 100; i++ {
-		list = append(list, []rune(fmt.Sprintf("com%d", i)))
-	}
-	line = line[:pos]
-	for _, r := range list {
-		if strings.HasPrefix(string(r), string(line)) {
-			newLine = append(newLine, r[len(line):])
-		}
-	}
-	return newLine, len(line)
-}
+var completer = readline.NewPrefixCompleter(
+	readline.PcItem("say",
+		readline.PcItem("hello"),
+		readline.PcItem("bye"),
+	),
+	readline.PcItem("bye"),
+	readline.PcItem("help"),
+	readline.PcItem("go",
+		readline.PcItem("build"),
+		readline.PcItem("install"),
+		readline.PcItem("test"),
+	),
+)
 
 func main() {
 	l, err := readline.NewEx(&readline.Config{
 		Prompt:       "\033[31m»\033[0m ",
 		HistoryFile:  "/tmp/readline.tmp",
-		AutoComplete: new(Completer),
+		AutoComplete: completer,
 	})
 	if err != nil {
 		panic(err)
@@ -54,18 +48,24 @@ func main() {
 		if err != nil {
 			break
 		}
-		switch line {
-		case "help":
+
+		switch {
+		case line == "help":
 			usage(l.Stderr())
-		case "sayhello":
+		case strings.HasPrefix(line, "say"):
+			line := strings.TrimSpace(line[3:])
+			if len(line) == 0 {
+				log.Println("say what?")
+				break
+			}
 			go func() {
 				for _ = range time.Tick(time.Second) {
-					log.Println("hello")
+					log.Println(line)
 				}
 			}()
-		case "bye":
+		case line == "bye":
 			goto exit
-		case "":
+		case line == "":
 		default:
 			log.Println("you said:", strconv.Quote(line))
 		}
diff --git a/readline.go b/readline.go
index 6da9267..864cfab 100644
--- a/readline.go
+++ b/readline.go
@@ -7,14 +7,6 @@ type Instance struct {
 	o *Operation
 }
 
-type AutoCompleter interface {
-	Do(line []rune, pos int) (newLine [][]rune, offset int)
-}
-
-type AutoCompleteHinter interface {
-	Hint(line []rune, pos int) ([]rune, bool)
-}
-
 type Config struct {
 	Prompt       string
 	HistoryFile  string
diff --git a/utils.go b/utils.go
index 2870d59..7b77634 100644
--- a/utils.go
+++ b/utils.go
@@ -270,3 +270,10 @@ func EqualRunes(r, r2 []rune) bool {
 	}
 	return true
 }
+
+func RunesHasPrefix(r, prefix []rune) bool {
+	if len(r) < len(prefix) {
+		return false
+	}
+	return EqualRunes(r[:len(prefix)], prefix)
+}