_content/talks/2011/lex/r59-lex.go - website - 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.

 // +build ignore

 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
 }

 func (i item) String() string {
 	switch {
 	case i.typ == itemEOF:
 		return "EOF"
 	case i.typ == itemError:
 		return i.val
 	case i.typ > itemKeyword:
 		return fmt.Sprintf("<%s>", i.val)
 	case len(i.val) > 10:
 		return fmt.Sprintf("%.10q...", i.val)
 	}
 	return fmt.Sprintf("%q", i.val)
 }

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

 const (
 	itemError   itemType = iota // error occurred; value is text of error
 	itemBool                    // boolean constant
 	itemComplex                 // complex constant (1+2i); imaginary is just a number
 	itemEOF
 	itemField      // alphanumeric identifier, starting with '.', possibly chained ('.x.y')
 	itemIdentifier // alphanumeric identifier
 	itemLeftDelim  // left action delimiter
 	itemNumber     // simple number, including imaginary
 	itemPipe       // pipe symbol
 	itemRawString  // raw quoted string (includes quotes)
 	itemRightDelim // right action delimiter
 	itemString     // quoted string (includes quotes)
 	itemText       // plain text
 	// Keywords appear after all the rest.
 	itemKeyword  // used only to delimit the keywords
 	itemDot      // the cursor, spelled '.'.
 	itemDefine   // define keyword
 	itemElse     // else keyword
 	itemEnd      // end keyword
 	itemIf       // if keyword
 	itemRange    // range keyword
 	itemTemplate // template keyword
 	itemWith     // with keyword
 )

 // Make the types prettyprint.
 var itemName = map[itemType]string{
 	itemError:      "error",
 	itemBool:       "bool",
 	itemComplex:    "complex",
 	itemEOF:        "EOF",
 	itemField:      "field",
 	itemIdentifier: "identifier",
 	itemLeftDelim:  "left delim",
 	itemNumber:     "number",
 	itemPipe:       "pipe",
 	itemRawString:  "raw string",
 	itemRightDelim: "right delim",
 	itemString:     "string",
 	// keywords
 	itemDot:      ".",
 	itemDefine:   "define",
 	itemElse:     "else",
 	itemIf:       "if",
 	itemEnd:      "end",
 	itemRange:    "range",
 	itemTemplate: "template",
 	itemWith:     "with",
 }

 func (i itemType) String() string {
 	s := itemName[i]
 	if s == "" {
 		return fmt.Sprintf("item%d", int(i))
 	}
 	return s
 }

 var key = map[string]itemType{
 	".":        itemDot,
 	"define":   itemDefine,
 	"else":     itemElse,
 	"end":      itemEnd,
 	"if":       itemIf,
 	"range":    itemRange,
 	"template": itemTemplate,
 	"with":     itemWith,
 }

 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.
 	state stateFn   // the next lexing function to enter
 	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) {
 		l.width = 0
 		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) {
 	l.items <- item{t, l.input[l.start:l.pos]}
 	l.start = l.pos
 }

 // ignore skips over the pending input 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) errorf(format string, args ...interface{}) stateFn {
 	l.items <- item{itemError, fmt.Sprintf(format, args...)}
 	return nil
 }

 // nextItem returns the next item from the input.
 func (l *lexer) nextItem() item {
 	for {
 		select {
 		case item := <-l.items:
 			return item
 		default:
 			l.state = l.state(l)
 		}
 	}
 	panic("not reached")
 }

 // lex creates a new scanner for the input string.
 func lex(name, input string) *lexer {
 	l := &lexer{
 		name:  name,
 		input: input,
 		state: lexText,
 		items: make(chan item, 2), // Two items sufficient.
 	}
 	return l
 }

 // state functions

 const (
 	leftDelim    = "{{"
 	rightDelim   = "}}"
 	leftComment  = "{{/*"
 	rightComment = "*/}}"
 )

 // lexText scans until an opening action delimiter, "{{".
 func lexText(l *lexer) stateFn {
 	for {
 		if strings.HasPrefix(l.input[l.pos:], leftDelim) {
 			if l.pos > l.start {
 				l.emit(itemText)
 			}
 			return lexLeftDelim
 		}
 		if l.next() == eof {
 			break
 		}
 	}
 	// Correctly reached EOF.
 	if l.pos > l.start {
 		l.emit(itemText)
 	}
 	l.emit(itemEOF)
 	return nil
 }

 // lexLeftDelim scans the left delimiter, which is known to be present.
 func lexLeftDelim(l *lexer) stateFn {
 	if strings.HasPrefix(l.input[l.pos:], leftComment) {
 		return lexComment
 	}
 	l.pos += len(leftDelim)
 	l.emit(itemLeftDelim)
 	return lexInsideAction
 }

 // lexComment scans a comment. The left comment marker is known to be present.
 func lexComment(l *lexer) stateFn {
 	i := strings.Index(l.input[l.pos:], rightComment)
 	if i < 0 {
 		return l.errorf("unclosed comment")
 	}
 	l.pos += i + len(rightComment)
 	l.ignore()
 	return lexText
 }

 // lexRightDelim scans the right delimiter, which is known to be present.
 func lexRightDelim(l *lexer) stateFn {
 	l.pos += len(rightDelim)
 	l.emit(itemRightDelim)
 	return lexText
 }

 // lexInsideAction scans the elements inside action delimiters.
 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:], rightDelim) {
 			return lexRightDelim
 		}
 		switch r := l.next(); {
 		case r == eof || r == '\n':
 			return l.errorf("unclosed action")
 		case isSpace(r):
 			l.ignore()
 		case r == '|':
 			l.emit(itemPipe)
 		case r == '"':
 			return lexQuote
 		case r == '`':
 			return lexRawQuote
 		case r == '.':
 			// special look-ahead for ".field" so we don't break l.backup().
 			if l.pos < len(l.input) {
 				r := l.input[l.pos]
 				if r < '0' || '9' < r {
 					return lexIdentifier // itemDot comes from the keyword table.
 				}
 			}
 			fallthrough // '.' can start a number.
 		case r == '+' || r == '-' || ('0' <= r && r <= '9'):
 			l.backup()
 			return lexNumber
 		case isAlphaNumeric(r):
 			l.backup()
 			return lexIdentifier
 		default:
 			return l.errorf("unrecognized character in action: %#U", r)
 		}
 	}
 	return nil
 }

 // lexIdentifier scans an alphanumeric or field.
 func lexIdentifier(l *lexer) stateFn {
 Loop:
 	for {
 		switch r := l.next(); {
 		case isAlphaNumeric(r):
 			// absorb.
 		case r == '.' && l.input[l.start] == '.':
 			// field chaining; absorb into one token.
 		default:
 			l.backup()
 			word := l.input[l.start:l.pos]
 			switch {
 			case key[word] > itemKeyword:
 				l.emit(key[word])
 			case word[0] == '.':
 				l.emit(itemField)
 			case word == "true", word == "false":
 				l.emit(itemBool)
 			default:
 				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.
 func lexNumber(l *lexer) stateFn {
 	if !l.scanNumber() {
 		return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
 	}
 	if sign := l.peek(); sign == '+' || sign == '-' {
 		// Complex: 1+2i.  No spaces, must end in 'i'.
 		if !l.scanNumber() || l.input[l.pos-1] != 'i' {
 			return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
 		}
 		l.emit(itemComplex)
 	} else {
 		l.emit(itemNumber)
 	}
 	return lexInsideAction
 }

 func (l *lexer) scanNumber() bool {
 	// 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 false
 	}
 	return true
 }

 // 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.errorf("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.errorf("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.

	// +build ignore

	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
	}

	func (i item) String() string {
	switch {
	case i.typ == itemEOF:
	return "EOF"
	case i.typ == itemError:
	return i.val
	case i.typ > itemKeyword:
	return fmt.Sprintf("<%s>", i.val)
	case len(i.val) > 10:
	return fmt.Sprintf("%.10q...", i.val)
	}
	return fmt.Sprintf("%q", i.val)
	}

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

	const (
	itemError itemType = iota // error occurred; value is text of error
	itemBool // boolean constant
	itemComplex // complex constant (1+2i); imaginary is just a number
	itemEOF
	itemField // alphanumeric identifier, starting with '.', possibly chained ('.x.y')
	itemIdentifier // alphanumeric identifier
	itemLeftDelim // left action delimiter
	itemNumber // simple number, including imaginary
	itemPipe // pipe symbol
	itemRawString // raw quoted string (includes quotes)
	itemRightDelim // right action delimiter
	itemString // quoted string (includes quotes)
	itemText // plain text
	// Keywords appear after all the rest.
	itemKeyword // used only to delimit the keywords
	itemDot // the cursor, spelled '.'.
	itemDefine // define keyword
	itemElse // else keyword
	itemEnd // end keyword
	itemIf // if keyword
	itemRange // range keyword
	itemTemplate // template keyword
	itemWith // with keyword
	)

	// Make the types prettyprint.
	var itemName = map[itemType]string{
	itemError: "error",
	itemBool: "bool",
	itemComplex: "complex",
	itemEOF: "EOF",
	itemField: "field",
	itemIdentifier: "identifier",
	itemLeftDelim: "left delim",
	itemNumber: "number",
	itemPipe: "pipe",
	itemRawString: "raw string",
	itemRightDelim: "right delim",
	itemString: "string",
	// keywords
	itemDot: ".",
	itemDefine: "define",
	itemElse: "else",
	itemIf: "if",
	itemEnd: "end",
	itemRange: "range",
	itemTemplate: "template",
	itemWith: "with",
	}

	func (i itemType) String() string {
	s := itemName[i]
	if s == "" {
	return fmt.Sprintf("item%d", int(i))
	}
	return s
	}

	var key = map[string]itemType{
	".": itemDot,
	"define": itemDefine,
	"else": itemElse,
	"end": itemEnd,
	"if": itemIf,
	"range": itemRange,
	"template": itemTemplate,
	"with": itemWith,
	}

	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.
	state stateFn // the next lexing function to enter
	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) {
	l.width = 0
	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) {
	l.items <- item{t, l.input[l.start:l.pos]}
	l.start = l.pos
	}

	// ignore skips over the pending input 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) errorf(format string, args ...interface{}) stateFn {
	l.items <- item{itemError, fmt.Sprintf(format, args...)}
	return nil
	}

	// nextItem returns the next item from the input.
	func (l *lexer) nextItem() item {
	for {
	select {
	case item := <-l.items:
	return item
	default:
	l.state = l.state(l)
	}
	}
	panic("not reached")
	}

	// lex creates a new scanner for the input string.
	func lex(name, input string) *lexer {
	l := &lexer{
	name: name,
	input: input,
	state: lexText,
	items: make(chan item, 2), // Two items sufficient.
	}
	return l
	}

	// state functions

	const (
	leftDelim = "{{"
	rightDelim = "}}"
	leftComment = "{{/*"
	rightComment = "*/}}"
	)

	// lexText scans until an opening action delimiter, "{{".
	func lexText(l *lexer) stateFn {
	for {
	if strings.HasPrefix(l.input[l.pos:], leftDelim) {
	if l.pos > l.start {
	l.emit(itemText)
	}
	return lexLeftDelim
	}
	if l.next() == eof {
	break
	}
	}
	// Correctly reached EOF.
	if l.pos > l.start {
	l.emit(itemText)
	}
	l.emit(itemEOF)
	return nil
	}

	// lexLeftDelim scans the left delimiter, which is known to be present.
	func lexLeftDelim(l *lexer) stateFn {
	if strings.HasPrefix(l.input[l.pos:], leftComment) {
	return lexComment
	}
	l.pos += len(leftDelim)
	l.emit(itemLeftDelim)
	return lexInsideAction
	}

	// lexComment scans a comment. The left comment marker is known to be present.
	func lexComment(l *lexer) stateFn {
	i := strings.Index(l.input[l.pos:], rightComment)
	if i < 0 {
	return l.errorf("unclosed comment")
	}
	l.pos += i + len(rightComment)
	l.ignore()
	return lexText
	}

	// lexRightDelim scans the right delimiter, which is known to be present.
	func lexRightDelim(l *lexer) stateFn {
	l.pos += len(rightDelim)
	l.emit(itemRightDelim)
	return lexText
	}

	// lexInsideAction scans the elements inside action delimiters.
	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:], rightDelim) {
	return lexRightDelim
	}
	switch r := l.next(); {
	case r == eof \|\| r == '\n':
	return l.errorf("unclosed action")
	case isSpace(r):
	l.ignore()
	case r == '\|':
	l.emit(itemPipe)
	case r == '"':
	return lexQuote
	case r == '`':
	return lexRawQuote
	case r == '.':
	// special look-ahead for ".field" so we don't break l.backup().
	if l.pos < len(l.input) {
	r := l.input[l.pos]
	if r < '0' \|\| '9' < r {
	return lexIdentifier // itemDot comes from the keyword table.
	}
	}
	fallthrough // '.' can start a number.
	case r == '+' \|\| r == '-' \|\| ('0' <= r && r <= '9'):
	l.backup()
	return lexNumber
	case isAlphaNumeric(r):
	l.backup()
	return lexIdentifier
	default:
	return l.errorf("unrecognized character in action: %#U", r)
	}
	}
	return nil
	}

	// lexIdentifier scans an alphanumeric or field.
	func lexIdentifier(l *lexer) stateFn {
	Loop:
	for {
	switch r := l.next(); {
	case isAlphaNumeric(r):
	// absorb.
	case r == '.' && l.input[l.start] == '.':
	// field chaining; absorb into one token.
	default:
	l.backup()
	word := l.input[l.start:l.pos]
	switch {
	case key[word] > itemKeyword:
	l.emit(key[word])
	case word[0] == '.':
	l.emit(itemField)
	case word == "true", word == "false":
	l.emit(itemBool)
	default:
	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.
	func lexNumber(l *lexer) stateFn {
	if !l.scanNumber() {
	return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
	}
	if sign := l.peek(); sign == '+' \|\| sign == '-' {
	// Complex: 1+2i. No spaces, must end in 'i'.
	if !l.scanNumber() \|\| l.input[l.pos-1] != 'i' {
	return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
	}
	l.emit(itemComplex)
	} else {
	l.emit(itemNumber)
	}
	return lexInsideAction
	}

	func (l *lexer) scanNumber() bool {
	// 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 false
	}
	return true
	}

	// 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.errorf("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.errorf("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)
	}