src/pkg/exp/template/lex.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package template

 import (
 	"fmt"
 	"strings"
 	"unicode"
 	"utf8"
 )

 // item represents a token or text string returned from the scanner.
 type item struct {
 	typ itemType
 	val string
 }

 // itemType identifies the type of lex item.
 type itemType int

 const (
 	itemError      itemType = iota // error occurred; value is text of error
 	itemText                       // plain text
 	itemLeftMeta                   // left meta-string
 	itemRightMeta                  // right meta-string
 	itemPipe                       // pipe symbol
 	itemIdentifier                 // alphanumeric identifier
 	itemNumber                     // number
 	itemRawString                  // raw quoted string (includes quotes)
 	itemString                     // quoted string (includes quotes)
 	itemEOF
 )

 const eof = -1

 // stateFn represents the state of the scanner as a function that returns the next state.
 type stateFn func(*lexer) stateFn

 // lexer holds the state of the scanner.
 type lexer struct {
 	name  string    // the name of the input; used only for error reports.
 	input string    // the string being scanned.
 	pos   int       // current position in the input.
 	start int       // start position of this item.
 	width int       // width of last rune read from input.
 	items chan item // channel of scanned items.
 }

 // next returns the next rune in the input.
 func (l *lexer) next() (rune int) {
 	if l.pos >= len(l.input) {
 		return eof
 	}
 	rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
 	l.pos += l.width
 	return rune
 }

 // peek returns but does not consume the next rune in the input.
 func (l *lexer) peek() int {
 	rune := l.next()
 	l.backup()
 	return rune
 }

 // backup steps back one rune. Can only be called once per call of next.
 func (l *lexer) backup() {
 	l.pos -= l.width
 }

 // emit passes an item back to the client.
 func (l *lexer) emit(t itemType) {
 	start := l.start
 	l.start = l.pos
 	l.items <- item{t, l.input[start:l.pos]}
 }

 // ignore discards whatever input is before this point.
 func (l *lexer) ignore() {
 	l.start = l.pos
 }

 // accept consumes the next rune if it's from the valid set.
 func (l *lexer) accept(valid string) bool {
 	if strings.IndexRune(valid, l.next()) >= 0 {
 		return true
 	}
 	l.backup()
 	return false
 }

 // acceptRun consumes a run of runes from the valid set.
 func (l *lexer) acceptRun(valid string) {
 	for strings.IndexRune(valid, l.next()) >= 0 {
 	}
 	l.backup()
 }

 // lineNumber reports which line we're on. Doing it this way
 // means we don't have to worry about peek double counting.
 func (l *lexer) lineNumber() int {
 	return 1 + strings.Count(l.input[:l.pos], "\n")
 }

 // error returns an error token and terminates the scan by passing
 // back a nil pointer that will be the next state, terminating l.run.
 func (l *lexer) error(format string, args ...interface{}) stateFn {
 	format = fmt.Sprintf("%s:%d %s", l.name, l.lineNumber(), format)
 	l.items <- item{itemError, fmt.Sprintf(format, args...)}
 	return nil
 }

 // run lexes the input by execute state functions until nil.
 func (l *lexer) run() {
 	for state := lexText; state != nil; {
 		state = state(l)
 	}
 	close(l.items)
 }

 // lex launches a new scanner and returns the channel of items.
 func lex(name, input string) chan item {
 	l := &lexer{
 		name:  name,
 		input: input,
 		items: make(chan item),
 	}
 	go l.run()
 	return l.items
 }

 // state functions

 const leftMeta = "{{"
 const rightMeta = "}}"

 // lexText scans until a metacharacter
 func lexText(l *lexer) stateFn {
 	for {
 		if strings.HasPrefix(l.input[l.pos:], leftMeta) {
 			if l.pos > l.start {
 				l.emit(itemText)
 			}
 			return lexLeftMeta
 		}
 		if l.next() == eof {
 			break
 		}
 	}
 	// Correctly reached EOF.
 	if l.pos > l.start {
 		l.emit(itemText)
 	}
 	l.emit(itemEOF)
 	return nil
 }

 // leftMeta scans the left "metacharacter", which is known to be present.
 func lexLeftMeta(l *lexer) stateFn {
 	l.pos += len(leftMeta)
 	l.emit(itemLeftMeta)
 	return lexInsideAction
 }

 // rightMeta scans the right "metacharacter", which is known to be present.
 func lexRightMeta(l *lexer) stateFn {
 	l.pos += len(rightMeta)
 	l.emit(itemRightMeta)
 	return lexText
 }

 // lexInsideAction scans the elements inside "metacharacters".
 func lexInsideAction(l *lexer) stateFn {
 	// Either number, quoted string, or identifier.
 	// Spaces separate and are ignored.
 	// Pipe symbols separate and are emitted.
 	for {
 		if strings.HasPrefix(l.input[l.pos:], rightMeta) {
 			return lexRightMeta
 		}
 		switch r := l.next(); {
 		case r == eof || r == '\n':
 			return l.error("unclosed action")
 		case isSpace(r):
 			l.ignore()
 		case r == '|':
 			l.emit(itemPipe)
 		case r == '"':
 			return lexQuote
 		case r == '`':
 			return lexRawQuote
 		case r == '+' || r == '-' || r == '.' || ('0' <= r && r <= '9'):
 			l.backup()
 			return lexNumber
 		case isAlphaNumeric(r):
 			l.backup()
 			return lexIdentifier
 		default:
 			return l.error("unrecognized character in action: %#U", r)
 		}
 	}
 	return nil
 }

 // lexIdentifier scans an alphanumeric.
 func lexIdentifier(l *lexer) stateFn {
 Loop:
 	for {
 		switch r := l.next(); {
 		case isAlphaNumeric(r):
 			// absorb
 		default:
 			l.backup()
 			l.emit(itemIdentifier)
 			break Loop
 		}
 	}
 	return lexInsideAction
 }

 // lexNumber scans a number: decimal, octal, hex, float, or imaginary.  This
 // isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
 // and "089" - but when it's wrong the input is invalid and the parser (via
 // strconv) will notice.
 // TODO: without expressions you can do imaginary but not complex.
 func lexNumber(l *lexer) stateFn {
 	// Optional leading sign.
 	l.accept("+-")
 	// Is it hex?
 	digits := "0123456789"
 	if l.accept("0") && l.accept("xX") {
 		digits = "0123456789abcdefABCDEF"
 	}
 	l.acceptRun(digits)
 	if l.accept(".") {
 		l.acceptRun(digits)
 	}
 	if l.accept("eE") {
 		l.accept("+-")
 		l.acceptRun("0123456789")
 	}
 	// Is it imaginary?
 	l.accept("i")
 	// Next thing mustn't be alphanumeric.
 	if isAlphaNumeric(l.peek()) {
 		l.next()
 		return l.error("bad number syntax: %q", l.input[l.start:l.pos])
 	}
 	l.emit(itemNumber)
 	return lexInsideAction
 }

 // lexQuote scans a quoted string.
 func lexQuote(l *lexer) stateFn {
 Loop:
 	for {
 		switch l.next() {
 		case '\\':
 			if r := l.next(); r != eof && r != '\n' {
 				break
 			}
 			fallthrough
 		case eof, '\n':
 			return l.error("unterminated quoted string")
 		case '"':
 			break Loop
 		}
 	}
 	l.emit(itemString)
 	return lexInsideAction
 }

 // lexRawQuote scans a raw quoted string.
 func lexRawQuote(l *lexer) stateFn {
 Loop:
 	for {
 		switch l.next() {
 		case eof, '\n':
 			return l.error("unterminated raw quoted string")
 		case '`':
 			break Loop
 		}
 	}
 	l.emit(itemRawString)
 	return lexInsideAction
 }

 // isSpace reports whether r is a space character.
 func isSpace(r int) bool {
 	switch r {
 	case ' ', '\t', '\n', '\r':
 		return true
 	}
 	return false
 }

 // isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
 func isAlphaNumeric(r int) bool {
 	return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package template

	import (
	"fmt"
	"strings"
	"unicode"
	"utf8"
	)

	// item represents a token or text string returned from the scanner.
	type item struct {
	typ itemType
	val string
	}

	// itemType identifies the type of lex item.
	type itemType int

	const (
	itemError itemType = iota // error occurred; value is text of error
	itemText // plain text
	itemLeftMeta // left meta-string
	itemRightMeta // right meta-string
	itemPipe // pipe symbol
	itemIdentifier // alphanumeric identifier
	itemNumber // number
	itemRawString // raw quoted string (includes quotes)
	itemString // quoted string (includes quotes)
	itemEOF
	)

	const eof = -1

	// stateFn represents the state of the scanner as a function that returns the next state.
	type stateFn func(*lexer) stateFn

	// lexer holds the state of the scanner.
	type lexer struct {
	name string // the name of the input; used only for error reports.
	input string // the string being scanned.
	pos int // current position in the input.
	start int // start position of this item.
	width int // width of last rune read from input.
	items chan item // channel of scanned items.
	}

	// next returns the next rune in the input.
	func (l *lexer) next() (rune int) {
	if l.pos >= len(l.input) {
	return eof
	}
	rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
	l.pos += l.width
	return rune
	}

	// peek returns but does not consume the next rune in the input.
	func (l *lexer) peek() int {
	rune := l.next()
	l.backup()
	return rune
	}

	// backup steps back one rune. Can only be called once per call of next.
	func (l *lexer) backup() {
	l.pos -= l.width
	}

	// emit passes an item back to the client.
	func (l *lexer) emit(t itemType) {
	start := l.start
	l.start = l.pos
	l.items <- item{t, l.input[start:l.pos]}
	}

	// ignore discards whatever input is before this point.
	func (l *lexer) ignore() {
	l.start = l.pos
	}

	// accept consumes the next rune if it's from the valid set.
	func (l *lexer) accept(valid string) bool {
	if strings.IndexRune(valid, l.next()) >= 0 {
	return true
	}
	l.backup()
	return false
	}

	// acceptRun consumes a run of runes from the valid set.
	func (l *lexer) acceptRun(valid string) {
	for strings.IndexRune(valid, l.next()) >= 0 {
	}
	l.backup()
	}

	// lineNumber reports which line we're on. Doing it this way
	// means we don't have to worry about peek double counting.
	func (l *lexer) lineNumber() int {
	return 1 + strings.Count(l.input[:l.pos], "\n")
	}

	// error returns an error token and terminates the scan by passing
	// back a nil pointer that will be the next state, terminating l.run.
	func (l *lexer) error(format string, args ...interface{}) stateFn {
	format = fmt.Sprintf("%s:%d %s", l.name, l.lineNumber(), format)
	l.items <- item{itemError, fmt.Sprintf(format, args...)}
	return nil
	}

	// run lexes the input by execute state functions until nil.
	func (l *lexer) run() {
	for state := lexText; state != nil; {
	state = state(l)
	}
	close(l.items)
	}

	// lex launches a new scanner and returns the channel of items.
	func lex(name, input string) chan item {
	l := &lexer{
	name: name,
	input: input,
	items: make(chan item),
	}
	go l.run()
	return l.items
	}

	// state functions

	const leftMeta = "{{"
	const rightMeta = "}}"

	// lexText scans until a metacharacter
	func lexText(l *lexer) stateFn {
	for {
	if strings.HasPrefix(l.input[l.pos:], leftMeta) {
	if l.pos > l.start {
	l.emit(itemText)
	}
	return lexLeftMeta
	}
	if l.next() == eof {
	break
	}
	}
	// Correctly reached EOF.
	if l.pos > l.start {
	l.emit(itemText)
	}
	l.emit(itemEOF)
	return nil
	}

	// leftMeta scans the left "metacharacter", which is known to be present.
	func lexLeftMeta(l *lexer) stateFn {
	l.pos += len(leftMeta)
	l.emit(itemLeftMeta)
	return lexInsideAction
	}

	// rightMeta scans the right "metacharacter", which is known to be present.
	func lexRightMeta(l *lexer) stateFn {
	l.pos += len(rightMeta)
	l.emit(itemRightMeta)
	return lexText
	}

	// lexInsideAction scans the elements inside "metacharacters".
	func lexInsideAction(l *lexer) stateFn {
	// Either number, quoted string, or identifier.
	// Spaces separate and are ignored.
	// Pipe symbols separate and are emitted.
	for {
	if strings.HasPrefix(l.input[l.pos:], rightMeta) {
	return lexRightMeta
	}
	switch r := l.next(); {
	case r == eof \|\| r == '\n':
	return l.error("unclosed action")
	case isSpace(r):
	l.ignore()
	case r == '\|':
	l.emit(itemPipe)
	case r == '"':
	return lexQuote
	case r == '`':
	return lexRawQuote
	case r == '+' \|\| r == '-' \|\| r == '.' \|\| ('0' <= r && r <= '9'):
	l.backup()
	return lexNumber
	case isAlphaNumeric(r):
	l.backup()
	return lexIdentifier
	default:
	return l.error("unrecognized character in action: %#U", r)
	}
	}
	return nil
	}

	// lexIdentifier scans an alphanumeric.
	func lexIdentifier(l *lexer) stateFn {
	Loop:
	for {
	switch r := l.next(); {
	case isAlphaNumeric(r):
	// absorb
	default:
	l.backup()
	l.emit(itemIdentifier)
	break Loop
	}
	}
	return lexInsideAction
	}

	// lexNumber scans a number: decimal, octal, hex, float, or imaginary. This
	// isn't a perfect number scanner - for instance it accepts "." and "0x0.2"
	// and "089" - but when it's wrong the input is invalid and the parser (via
	// strconv) will notice.
	// TODO: without expressions you can do imaginary but not complex.
	func lexNumber(l *lexer) stateFn {
	// Optional leading sign.
	l.accept("+-")
	// Is it hex?
	digits := "0123456789"
	if l.accept("0") && l.accept("xX") {
	digits = "0123456789abcdefABCDEF"
	}
	l.acceptRun(digits)
	if l.accept(".") {
	l.acceptRun(digits)
	}
	if l.accept("eE") {
	l.accept("+-")
	l.acceptRun("0123456789")
	}
	// Is it imaginary?
	l.accept("i")
	// Next thing mustn't be alphanumeric.
	if isAlphaNumeric(l.peek()) {
	l.next()
	return l.error("bad number syntax: %q", l.input[l.start:l.pos])
	}
	l.emit(itemNumber)
	return lexInsideAction
	}

	// lexQuote scans a quoted string.
	func lexQuote(l *lexer) stateFn {
	Loop:
	for {
	switch l.next() {
	case '\\':
	if r := l.next(); r != eof && r != '\n' {
	break
	}
	fallthrough
	case eof, '\n':
	return l.error("unterminated quoted string")
	case '"':
	break Loop
	}
	}
	l.emit(itemString)
	return lexInsideAction
	}

	// lexRawQuote scans a raw quoted string.
	func lexRawQuote(l *lexer) stateFn {
	Loop:
	for {
	switch l.next() {
	case eof, '\n':
	return l.error("unterminated raw quoted string")
	case '`':
	break Loop
	}
	}
	l.emit(itemRawString)
	return lexInsideAction
	}

	// isSpace reports whether r is a space character.
	func isSpace(r int) bool {
	switch r {
	case ' ', '\t', '\n', '\r':
	return true
	}
	return false
	}

	// isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
	func isAlphaNumeric(r int) bool {
	return r == '_' \|\| unicode.IsLetter(r) \|\| unicode.IsDigit(r)
	}