testable lexer, in theory

lexer.go

@@ -1,200 +1,245 @@
+//go:generate stringer -type=ItemType
 package wikilink
 
 import (
 	"fmt"
+	"log"
 	"strings"
 	"unicode/utf8"
 )
 
 const (
-	eof rune = -1
+	ItemError ItemType = iota
+	ItemEOF
+	ItemText
+	ItemOpenLink
+	ItemCloseLink
+	ItemFragment
+	ItemAlias
 )
 
 const (
-	openLink  = "[["
-	closeLink = "]]"
-	alias     = "|"
-	blockRef  = "#^"
+	EOF rune = 0
 )
 
-func lex(name, input string) *lexer {
-	l := &lexer{
+const (
+	OpenLink  = "[["
+	CloseLink = "]]"
+	Alias     = "|"
+	BlockRef  = "#^"
+)
+
+func Lex(name, input string) *Lexer {
+	l := &Lexer{
 		name:  name,
 		input: input,
 		state: lexText,
-		items: make(chan item, 2),
+		items: make(chan Item, 2),
 	}
 	go l.run()
+
 	return l
 }
 
-func (l *lexer) nextItem() item {
+func (l *Lexer) NextItem() Item {
 	for {
 		select {
 		case item := <-l.items:
 			return item
 		default:
+			if l.state == nil {
+				return Item{
+					Typ: ItemError,
+					Val: "state is nil, should not be",
+				}
+			}
+
 			l.state = l.state(l)
 		}
 	}
 }
 
-func (l *lexer) ignore() {
+func (l *Lexer) ignore() {
 	l.start = l.pos
 }
 
-func (l *lexer) backup() {
+func (l *Lexer) backup() {
 	l.pos -= l.width
 }
 
-type lexer struct {
+type Lexer struct {
 	name, input       string
 	start, pos, width int
 	state             stateFn
-	items             chan item
+	items             chan Item
 }
 
-func (l *lexer) peek() rune {
+func (l *Lexer) peek() rune {
 	r := l.next()
 	l.backup()
+
 	return r
 }
 
-func (l *lexer) accept(valid string) bool {
-	if strings.IndexRune(valid, l.next()) >= 0 {
+func (l *Lexer) accept(valid string) bool {
+	if strings.ContainsRune(valid, l.next()) {
 		return true
 	}
+
 	l.backup()
+
 	return false
 }
 
-func (l *lexer) acceptRun(valid string) {
-	for strings.IndexRune(valid, l.next()) >= 0 {
+func (l *Lexer) acceptRun(valid string) {
+	for strings.ContainsRune(valid, l.next()) {
 	}
 	l.backup()
 }
 
-func (l *lexer) emit(t itemType) {
-	l.items <- item{t, l.input[l.start:l.pos]}
+func (l *Lexer) emit(t ItemType) {
+	i := Item{t, l.input[l.start:l.pos]}
+	log.Printf("emitting Item: %#+v\n", i)
+	l.items <- i
 	l.start = l.pos
 }
 
-func (l *lexer) errorf(format string, args ...interface{}) stateFn {
-	l.items <- item{
-		itemError,
+func (l *Lexer) errorf(format string, args ...interface{}) stateFn {
+	log.Printf("entering errorf: %q\n", format)
+	l.items <- Item{
+		ItemError,
 		fmt.Sprintf(format, args...),
 	}
+
 	return nil
 }
 
-func lexFragment(l *lexer) stateFn {
-	return l.errorf("lexFragment not implemented")
+func lexFragment(l *Lexer) stateFn {
+	log.Println("entering lexFragment")
+	for {
+		if strings.HasPrefix(l.input[l.pos:], CloseLink) {
+			return lexCloseLink
+		}
+
+		if l.peek() == '^' {
+			l.next()
+			l.emit(ItemFragment)
+			l.acceptRun("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 -.,")
+
+			return lexInsideLink
+		}
+
+		return lexInsideLink
+	}
 }
 
-func lexAlias(l *lexer) stateFn {
-	return l.errorf("lexAlias not implemented")
+func lexAlias(l *Lexer) stateFn {
+	// l.accept
+	log.Println("entering lexAlias")
+	return lexInsideLink
 }
 
-func lexInsideLink(l *lexer) stateFn {
+func lexInsideLink(l *Lexer) stateFn {
+	log.Println("entering lexInsideLink")
 	for {
-		if strings.HasPrefix(l.input[l.pos:], closeLink) {
+		if strings.HasPrefix(l.input[l.pos:], CloseLink) {
 			return lexCloseLink
 		}
 
 		r := l.next()
 
 		switch {
-		case r == eof:
+		case r == EOF:
 		case r == '\n':
 			return l.errorf("unclosed link")
 		case r == '#':
+			l.emit(ItemText)
 			return lexFragment
 		case r == '|':
+			l.emit(ItemText)
 			return lexAlias
+		case l.peek() == ']':
+			l.emit(ItemText)
+			return lexCloseLink
 		}
 	}
 }
 
-func lexOpenLink(l *lexer) stateFn {
-	l.pos += len(openLink)
-	l.emit(itemOpenLink)
+func lexOpenLink(l *Lexer) stateFn {
+	log.Println("entering lexOpenLink")
+	l.pos += len(OpenLink)
+	l.emit(ItemOpenLink)
 	return lexInsideLink
 }
 
-func lexCloseLink(l *lexer) stateFn {
-	l.pos += len(closeLink)
-	l.emit(itemCloseLink)
+func lexCloseLink(l *Lexer) stateFn {
+	log.Println("entering lexCloseLink")
+	l.pos += len(CloseLink)
+	l.emit(ItemCloseLink)
 	return lexText
 }
 
-func lexText(l *lexer) stateFn {
+func lexText(l *Lexer) stateFn {
+	log.Println("entering lexText")
+
 	for {
-		if strings.HasPrefix(l.input[l.pos:], openLink) {
+		if strings.HasPrefix(l.input[l.pos:], OpenLink) {
 			if l.pos > l.start {
-				l.emit(itemText)
+				l.emit(ItemText)
 			}
 			return lexOpenLink
 		}
 
-		if l.next() == eof {
+		if l.next() == EOF {
 			break
 		}
 		if l.pos > l.start {
-			l.emit(itemText)
+			l.emit(ItemText)
 		}
-		l.emit(itemEOF)
+		l.emit(ItemEOF)
 		return nil
 	}
 	return nil
 }
 
-func (l *lexer) next() rune {
+func (l *Lexer) next() rune {
 	var r rune
 	if l.pos >= len(l.input) {
 		l.width = 0
-		return eof
+		return EOF
 	}
 	r, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
 	l.pos += l.width
 	return r
 }
 
-func (l *lexer) run() {
+func (l *Lexer) run() {
 	for state := lexText; state != nil; {
 		state = state(l)
 	}
 	close(l.items)
 }
 
-type stateFn func(*lexer) stateFn
+type stateFn func(*Lexer) stateFn
 
-type itemType int
+type ItemType int
 
-const (
-	itemError itemType = iota
-	itemEOF
-	itemText
-	itemOpenLink
-	itemCloseLink
-	itemBlockRef
-	itemAlias
-)
-
-type item struct {
-	typ itemType
-	val string
+type Item struct {
+	Typ ItemType
+	Val string
 }
 
-func (i item) String() string {
-	switch i.typ {
+func (i Item) String() string {
+	switch i.Typ {
 
-	case itemEOF:
+	case ItemEOF:
 		return "EOF"
-	case itemError:
-		return i.val
+	case ItemError:
+		return i.Val
 	}
-	if len(i.val) > 10 {
-		return fmt.Sprintf("%.10q...", i.val)
+
+	if len(i.Val) > 10 {
+		return fmt.Sprintf("%s:%.10q...", i.Typ, i.Val)
 	}
-	return fmt.Sprintf("%q...", i.val)
+	return fmt.Sprintf("%s:%q...", i.Typ, i.Val)
 }