Simplifying lexer

lex.go

@@ -12,12 +12,12 @@ func main() {
 	f, _ := os.Open("test.json")
 	b, _ := ioutil.ReadAll(f)
 
-	lex := lexer.New("foo", string(b))
+	lex := lexer.New(string(b))
 	go lex.Run()
 	for {
-		i := lex.NextItem()
+		if item, ok := lex.NextItem(); ok {
-		fmt.Println(i)
+			fmt.Println(item)
-		if i.String() == "EOF" {
+		} else {
 			break
 		}
 	}

lexer/lexer.go

@@ -15,48 +15,42 @@ type (
 		pos     int       // current position in the input
 		start   int       // start position of this item
 		width   int       // width of last rune read from input
-		lastPos    int       // position of most recent item returned by nextItem
 		items   chan Item // channel of scanned items
-		parenDepth int       // nesting depth of ( ) exprs
 	}
 
+	// Item represents a token or text string returned from the scanner.
+	Item struct {
+		Token Token  // The type of this item.
+		Pos   int    // The starting position, in bytes, of this item in the input string.
+		Val   string // The value of this item.
+	}
+
+	// Token identifies the type of lex items.
+	Token int
+
 	// stateFn represents the state of the scanner as a function that returns the next state.
 	stateFn func(*Lexer) stateFn
-
-	// item represents a token or text string returned from the scanner.
-	Item struct {
-		typ itemType // The type of this item.
-		pos int      // The starting position, in bytes, of this item in the input string.
-		val string   // The value of this item.
-	}
-
-	// itemType identifies the type of lex items.
-	itemType int
 )
 
 const (
 	// Special
-	itemError itemType = iota // error occurred; value is text of error
+	Error Token = iota // error occurred; value is text of error
-	itemEOF
+	EOF
 
 	// Symbols
-	itemBraceOpen    // {
+	BraceOpen    // {
-	itemBraceClose   // }
+	BraceClose   // }
-	itemBracketOpen  // [
+	BracketOpen  // [
-	itemBracketClose // [
+	BracketClose // [
-	itemQuote        // "
+	Quote        // "
-	itemColon        // :
+	Colon        // :
-	itemComma        // ,
+	Comma        // ,
 
 	// Types
-	itemNull   // null
+	Null   // null
-	itemBool   // true, false
+	Bool   // true, false
-	itemNumber // 0, 2.5
+	Number // 0, 2.5
-	itemString // "foo"
+	String // "foo"
-)
-
-const (
-	EOF = -1
 )
 
 // lex creates a new scanner for the input string.
@@ -75,10 +69,9 @@ func (l *Lexer) Run() {
 	}
 }
 
-func (l *Lexer) NextItem() Item {
+func (l *Lexer) NextItem() (item Item, ok bool) {
-	item := <-l.items
+	item, ok = <-l.items
-	l.lastPos = item.pos
+	return
-	return item
 }
 
 //
@@ -86,33 +79,33 @@ func (l *Lexer) NextItem() Item {
 //
 
 func (i Item) String() string {
-	switch i.typ {
+	switch i.Token {
-	case itemEOF:
+	case EOF:
 		return "EOF"
-	case itemError:
+	case Error:
-		return "Error: " + i.val
+		return "Error: " + i.Val
-	case itemBraceOpen:
+	case BraceOpen:
 		return "{"
-	case itemBraceClose:
+	case BraceClose:
 		return "}"
-	case itemBracketOpen:
+	case BracketOpen:
 		return "["
-	case itemBracketClose:
+	case BracketClose:
 		return "]"
-	case itemQuote:
+	case Quote:
 		return "\""
-	case itemColon:
+	case Colon:
 		return ":"
-	case itemComma:
+	case Comma:
 		return ","
-	case itemNull:
+	case Null:
 		return "NULL"
-	case itemBool:
+	case Bool:
-		return "Bool: " + i.val
+		return "Bool: " + i.Val
-	case itemNumber:
+	case Number:
-		return "Number: " + i.val
+		return "Number: " + i.Val
-	case itemString:
+	case String:
-		return "String: " + i.val
+		return "String: " + i.Val
 	default:
 		panic("Unreachable")
 	}
@@ -122,7 +115,7 @@ func (i Item) String() string {
 func (l *Lexer) next() rune {
 	if int(l.pos) >= len(l.input) {
 		l.width = 0
-		return EOF
+		return 0
 	}
 	r, w := utf8.DecodeRuneInString(l.input[l.pos:])
 	l.width = w
@@ -143,9 +136,12 @@ func (l *Lexer) backup() {
 }
 
 // emit passes an item back to the client.
-func (l *Lexer) emit(t itemType) {
+func (l *Lexer) emit(t Token) {
 	l.items <- Item{t, l.start, l.input[l.start:l.pos]}
 	l.start = l.pos
+	if t == EOF {
+		close(l.items)
+	}
 }
 
 // ignore skips over the pending input before this point.
@@ -161,9 +157,135 @@ func (l *Lexer) acceptString(s string) (ok bool) {
 	return false
 }
 
-// errorf returns an error token and terminates the scan by passing
-// back a nil pointer that will be the next state, terminating l.nextItem.
 func (l *Lexer) errorf(format string, args ...interface{}) stateFn {
-	l.items <- Item{itemError, l.start, fmt.Sprintf(format, args...)}
+	l.items <- Item{Error, l.start, fmt.Sprintf(format, args...)}
+	return nil // Stop lexing
+}
+
+//
+// States
+//
+
+func lexInitial(l *Lexer) stateFn {
+loop:
+	for {
+		switch r := l.next(); r {
+		case ' ', '\t':
+			return lexSpace(l)
+		case '\n':
+			l.lineNum++
+		case 'n':
+			l.backup()
+			return lexNull(l)
+		case 't', 'f':
+			l.backup()
+			return lexBool(l)
+		case '1', '2', '3', '4', '5', '6', '7', '8', '9', '0':
+			l.backup()
+			return lexNumber(l)
+		case '"':
+			return lexString(l)
+		case '[':
+			l.emit(BracketOpen)
+		case ']':
+			l.emit(BracketClose)
+		case '{':
+			l.emit(BraceOpen)
+		case '}':
+			l.emit(BraceClose)
+		case ':':
+			l.emit(Colon)
+		case ',':
+			l.emit(Comma)
+		case 0:
+			break loop
+		default:
+			panic("Unexpected symbol: " + string(r))
+		}
+	}
+
+	// Correctly reached EOF.
+	l.emit(EOF)
+
 	return nil
 }
+
+// Skip all spaces
+// One space has already been seen
+func lexSpace(l *Lexer) stateFn {
+	for {
+		if r := l.peek(); r == ' ' || r == '\t' {
+			l.next()
+		} else {
+			break
+		}
+	}
+	l.ignore()
+
+	return lexInitial
+}
+
+func lexNull(l *Lexer) stateFn {
+	if l.acceptString("null") {
+		l.emit(Null)
+	} else {
+		return l.errorf("Unexpected token")
+	}
+	return lexInitial
+}
+
+func lexBool(l *Lexer) stateFn {
+	if l.acceptString("true") || l.acceptString("false") {
+		l.emit(Bool)
+	}
+	return lexInitial
+}
+
+func lexNumber(l *Lexer) stateFn {
+	hasDot := false
+loop:
+	for {
+		switch r := l.peek(); r {
+		case '1', '2', '3', '4', '5', '6', '7', '8', '9', '0':
+			l.next()
+		case '.':
+			if hasDot {
+				return l.errorf("Invalid number")
+			} else {
+				hasDot = true
+				l.next()
+			}
+		default:
+			break loop
+		}
+	}
+
+	l.emit(Number)
+	return lexInitial
+}
+
+func lexString(l *Lexer) stateFn {
+	escaped := false
+loop:
+	for {
+		switch r := l.next(); r {
+		case '\\':
+			escaped = true
+		case '"':
+			if escaped {
+				escaped = false
+			} else {
+				l.emit(String)
+				break loop
+			}
+		case '\n':
+			l.lineNum++
+		case 0:
+			return l.errorf("Unterminated string")
+		default:
+			escaped = false
+		}
+	}
+
+	return lexInitial
+}

lexer/state.go

@@ -1,128 +0,0 @@
-package lexer
-
-import "strings"
-
-func lexInitial(l *Lexer) stateFn {
-loop:
-	for {
-		switch r := l.next(); r {
-		case ' ', '\t':
-			return lexSpace(l)
-		case '\n':
-			l.lineNum++
-		case 'n':
-			l.backup()
-			return lexNull(l)
-		case 't', 'f':
-			l.backup()
-			return lexBool(l)
-		case '1', '2', '3', '4', '5', '6', '7', '8', '9', '0':
-			l.backup()
-			return lexNumber(l)
-		case '"':
-			return lexString(l)
-		case '[':
-			l.emit(itemBracketOpen)
-		case ']':
-			l.emit(itemBracketClose)
-		case '{':
-			l.emit(itemBraceOpen)
-		case '}':
-			l.emit(itemBraceClose)
-		case ':':
-			l.emit(itemColon)
-		case ',':
-			l.emit(itemComma)
-		case EOF:
-			break loop
-		default:
-			panic("Unexpected symbol: " + string(r))
-		}
-	}
-
-	// Correctly reached EOF.
-	l.emit(itemEOF)
-
-	return nil
-}
-
-// Skip all spaces
-// One space has already been seen
-func lexSpace(l *Lexer) stateFn {
-	for isSpace(l.peek()) {
-		l.next()
-	}
-	l.ignore()
-	return lexInitial
-}
-
-func lexNull(l *Lexer) stateFn {
-	if l.acceptString("null") {
-		l.emit(itemNull)
-	} else {
-		return l.errorf("Unexpected token")
-	}
-	return lexInitial
-}
-
-func lexBool(l *Lexer) stateFn {
-	if l.acceptString("true") || l.acceptString("false") {
-		l.emit(itemBool)
-	}
-	return lexInitial
-}
-
-func lexNumber(l *Lexer) stateFn {
-	hasDot := false
-	for {
-		if r := l.peek(); isDigit(r) {
-			l.next()
-		} else if r == '.' {
-			if hasDot {
-				return l.errorf("Invalid number")
-			} else {
-				hasDot = true
-				l.next()
-			}
-		} else {
-			break
-		}
-	}
-
-	l.emit(itemNumber)
-	return lexInitial
-}
-
-func lexString(l *Lexer) stateFn {
-	escaped := false
-loop:
-	for {
-		switch r := l.next(); r {
-		case '\\':
-			escaped = true
-		case '"':
-			if escaped {
-				escaped = false
-			} else {
-				l.emit(itemString)
-				break loop
-			}
-		case '\n':
-			l.lineNum++
-		case EOF:
-			return l.errorf("String hits EOF")
-		default:
-			escaped = false
-		}
-	}
-
-	return lexInitial
-}
-
-func isSpace(r rune) bool {
-	return r == ' ' || r == '\t'
-}
-
-func isDigit(r rune) bool {
-	return strings.IndexRune("1234567890", r) > -1
-}

test.json

@@ -9,5 +9,8 @@
         {"length": 13, "weight": 5},
         {"length": 18, "weight": 8},
         {"length": 13, "weight": 4}
-    ]
+    ],
+    "misc": {
+        "string with quotes": "beware of \"quoted\" text"
+    }
 }