libgo/go/text/template/parse/lex.go - rust-lang/gcc - 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 parse

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

 // item represents a token or text string returned from the scanner.
 type item struct {
 	typ  itemType // The type of this item.
 	pos  Pos      // The starting position, in bytes, of this item in the input string.
 	val  string   // The value of this item.
 	line int      // The line number at the start of this item.
 }

 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
 	itemChar                         // printable ASCII character; grab bag for comma etc.
 	itemCharConstant                 // character constant
 	itemComplex                      // complex constant (1+2i); imaginary is just a number
 	itemColonEquals                  // colon-equals (':=') introducing a declaration
 	itemEOF
 	itemField      // alphanumeric identifier starting with '.'
 	itemIdentifier // alphanumeric identifier not starting with '.'
 	itemLeftDelim  // left action delimiter
 	itemLeftParen  // '(' inside action
 	itemNumber     // simple number, including imaginary
 	itemPipe       // pipe symbol
 	itemRawString  // raw quoted string (includes quotes)
 	itemRightDelim // right action delimiter
 	itemRightParen // ')' inside action
 	itemSpace      // run of spaces separating arguments
 	itemString     // quoted string (includes quotes)
 	itemText       // plain text
 	itemVariable   // variable starting with '$', such as '$' or  '$1' or '$hello'
 	// Keywords appear after all the rest.
 	itemKeyword  // used only to delimit the keywords
 	itemBlock    // block keyword
 	itemDot      // the cursor, spelled '.'
 	itemDefine   // define keyword
 	itemElse     // else keyword
 	itemEnd      // end keyword
 	itemIf       // if keyword
 	itemNil      // the untyped nil constant, easiest to treat as a keyword
 	itemRange    // range keyword
 	itemTemplate // template keyword
 	itemWith     // with keyword
 )

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

 const eof = -1

 // Trimming spaces.
 // If the action begins "{{- " rather than "{{", then all space/tab/newlines
 // preceding the action are trimmed; conversely if it ends " -}}" the
 // leading spaces are trimmed. This is done entirely in the lexer; the
 // parser never sees it happen. We require an ASCII space to be
 // present to avoid ambiguity with things like "{{-3}}". It reads
 // better with the space present anyway. For simplicity, only ASCII
 // space does the job.
 const (
 	spaceChars      = " \t\r\n" // These are the space characters defined by Go itself.
 	leftTrimMarker  = "- "      // Attached to left delimiter, trims trailing spaces from preceding text.
 	rightTrimMarker = " -"      // Attached to right delimiter, trims leading spaces from following text.
 	trimMarkerLen   = Pos(len(leftTrimMarker))
 )

 // 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
 	leftDelim  string    // start of action
 	rightDelim string    // end of action
 	state      stateFn   // the next lexing function to enter
 	pos        Pos       // current position in the input
 	start      Pos       // start position of this item
 	width      Pos       // width of last rune read from input
 	lastPos    Pos       // position of most recent item returned by nextItem
 	items      chan item // channel of scanned items
 	parenDepth int       // nesting depth of ( ) exprs
 	line       int       // 1+number of newlines seen
 }

 // next returns the next rune in the input.
 func (l *lexer) next() rune {
 	if int(l.pos) >= len(l.input) {
 		l.width = 0
 		return eof
 	}
 	r, w := utf8.DecodeRuneInString(l.input[l.pos:])
 	l.width = Pos(w)
 	l.pos += l.width
 	if r == '\n' {
 		l.line++
 	}
 	return r
 }

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

 // backup steps back one rune. Can only be called once per call of next.
 func (l *lexer) backup() {
 	l.pos -= l.width
 	// Correct newline count.
 	if l.width == 1 && l.input[l.pos] == '\n' {
 		l.line--
 	}
 }

 // emit passes an item back to the client.
 func (l *lexer) emit(t itemType) {
 	l.items <- item{t, l.start, l.input[l.start:l.pos], l.line}
 	// Some items contain text internally. If so, count their newlines.
 	switch t {
 	case itemText, itemRawString, itemLeftDelim, itemRightDelim:
 		l.line += strings.Count(l.input[l.start:l.pos], "\n")
 	}
 	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.ContainsRune(valid, l.next()) {
 		return true
 	}
 	l.backup()
 	return false
 }

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

 // 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.line}
 	return nil
 }

 // nextItem returns the next item from the input.
 // Called by the parser, not in the lexing goroutine.
 func (l *lexer) nextItem() item {
 	item := <-l.items
 	l.lastPos = item.pos
 	return item
 }

 // drain drains the output so the lexing goroutine will exit.
 // Called by the parser, not in the lexing goroutine.
 func (l *lexer) drain() {
 	for range l.items {
 	}
 }

 // lex creates a new scanner for the input string.
 func lex(name, input, left, right string) *lexer {
 	if left == "" {
 		left = leftDelim
 	}
 	if right == "" {
 		right = rightDelim
 	}
 	l := &lexer{
 		name:       name,
 		input:      input,
 		leftDelim:  left,
 		rightDelim: right,
 		items:      make(chan item),
 		line:       1,
 	}
 	go l.run()
 	return l
 }

 // run runs the state machine for the lexer.
 func (l *lexer) run() {
 	for l.state = lexText; l.state != nil; {
 		l.state = l.state(l)
 	}
 	close(l.items)
 }

 // state functions

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

 // lexText scans until an opening action delimiter, "{{".
 func lexText(l *lexer) stateFn {
 	l.width = 0
 	if x := strings.Index(l.input[l.pos:], l.leftDelim); x >= 0 {
 		ldn := Pos(len(l.leftDelim))
 		l.pos += Pos(x)
 		trimLength := Pos(0)
 		if strings.HasPrefix(l.input[l.pos+ldn:], leftTrimMarker) {
 			trimLength = rightTrimLength(l.input[l.start:l.pos])
 		}
 		l.pos -= trimLength
 		if l.pos > l.start {
 			l.emit(itemText)
 		}
 		l.pos += trimLength
 		l.ignore()
 		return lexLeftDelim
 	} else {
 		l.pos = Pos(len(l.input))
 	}
 	// Correctly reached EOF.
 	if l.pos > l.start {
 		l.emit(itemText)
 	}
 	l.emit(itemEOF)
 	return nil
 }

 // rightTrimLength returns the length of the spaces at the end of the string.
 func rightTrimLength(s string) Pos {
 	return Pos(len(s) - len(strings.TrimRight(s, spaceChars)))
 }

 // atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
 func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
 	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
 		return true, false
 	}
 	// The right delim might have the marker before.
 	if strings.HasPrefix(l.input[l.pos:], rightTrimMarker) {
 		if strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) {
 			return true, true
 		}
 	}
 	return false, false
 }

 // leftTrimLength returns the length of the spaces at the beginning of the string.
 func leftTrimLength(s string) Pos {
 	return Pos(len(s) - len(strings.TrimLeft(s, spaceChars)))
 }

 // lexLeftDelim scans the left delimiter, which is known to be present, possibly with a trim marker.
 func lexLeftDelim(l *lexer) stateFn {
 	l.pos += Pos(len(l.leftDelim))
 	trimSpace := strings.HasPrefix(l.input[l.pos:], leftTrimMarker)
 	afterMarker := Pos(0)
 	if trimSpace {
 		afterMarker = trimMarkerLen
 	}
 	if strings.HasPrefix(l.input[l.pos+afterMarker:], leftComment) {
 		l.pos += afterMarker
 		l.ignore()
 		return lexComment
 	}
 	l.emit(itemLeftDelim)
 	l.pos += afterMarker
 	l.ignore()
 	l.parenDepth = 0
 	return lexInsideAction
 }

 // lexComment scans a comment. The left comment marker is known to be present.
 func lexComment(l *lexer) stateFn {
 	l.pos += Pos(len(leftComment))
 	i := strings.Index(l.input[l.pos:], rightComment)
 	if i < 0 {
 		return l.errorf("unclosed comment")
 	}
 	l.pos += Pos(i + len(rightComment))
 	delim, trimSpace := l.atRightDelim()
 	if !delim {
 		return l.errorf("comment ends before closing delimiter")
 	}
 	if trimSpace {
 		l.pos += trimMarkerLen
 	}
 	l.pos += Pos(len(l.rightDelim))
 	if trimSpace {
 		l.pos += leftTrimLength(l.input[l.pos:])
 	}
 	l.ignore()
 	return lexText
 }

 // lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
 func lexRightDelim(l *lexer) stateFn {
 	trimSpace := strings.HasPrefix(l.input[l.pos:], rightTrimMarker)
 	if trimSpace {
 		l.pos += trimMarkerLen
 		l.ignore()
 	}
 	l.pos += Pos(len(l.rightDelim))
 	l.emit(itemRightDelim)
 	if trimSpace {
 		l.pos += leftTrimLength(l.input[l.pos:])
 		l.ignore()
 	}
 	return lexText
 }

 // lexInsideAction scans the elements inside action delimiters.
 func lexInsideAction(l *lexer) stateFn {
 	// Either number, quoted string, or identifier.
 	// Spaces separate arguments; runs of spaces turn into itemSpace.
 	// Pipe symbols separate and are emitted.
 	delim, _ := l.atRightDelim()
 	if delim {
 		if l.parenDepth == 0 {
 			return lexRightDelim
 		}
 		return l.errorf("unclosed left paren")
 	}
 	switch r := l.next(); {
 	case r == eof || isEndOfLine(r):
 		return l.errorf("unclosed action")
 	case isSpace(r):
 		return lexSpace
 	case r == ':':
 		if l.next() != '=' {
 			return l.errorf("expected :=")
 		}
 		l.emit(itemColonEquals)
 	case r == '|':
 		l.emit(itemPipe)
 	case r == '"':
 		return lexQuote
 	case r == '`':
 		return lexRawQuote
 	case r == '$':
 		return lexVariable
 	case r == '\'':
 		return lexChar
 	case r == '.':
 		// special look-ahead for ".field" so we don't break l.backup().
 		if l.pos < Pos(len(l.input)) {
 			r := l.input[l.pos]
 			if r < '0' || '9' < r {
 				return lexField
 			}
 		}
 		fallthrough // '.' can start a number.
 	case r == '+' || r == '-' || ('0' <= r && r <= '9'):
 		l.backup()
 		return lexNumber
 	case isAlphaNumeric(r):
 		l.backup()
 		return lexIdentifier
 	case r == '(':
 		l.emit(itemLeftParen)
 		l.parenDepth++
 	case r == ')':
 		l.emit(itemRightParen)
 		l.parenDepth--
 		if l.parenDepth < 0 {
 			return l.errorf("unexpected right paren %#U", r)
 		}
 	case r <= unicode.MaxASCII && unicode.IsPrint(r):
 		l.emit(itemChar)
 		return lexInsideAction
 	default:
 		return l.errorf("unrecognized character in action: %#U", r)
 	}
 	return lexInsideAction
 }

 // lexSpace scans a run of space characters.
 // One space has already been seen.
 func lexSpace(l *lexer) stateFn {
 	for isSpace(l.peek()) {
 		l.next()
 	}
 	l.emit(itemSpace)
 	return lexInsideAction
 }

 // lexIdentifier scans an alphanumeric.
 func lexIdentifier(l *lexer) stateFn {
 Loop:
 	for {
 		switch r := l.next(); {
 		case isAlphaNumeric(r):
 			// absorb.
 		default:
 			l.backup()
 			word := l.input[l.start:l.pos]
 			if !l.atTerminator() {
 				return l.errorf("bad character %#U", r)
 			}
 			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
 }

 // lexField scans a field: .Alphanumeric.
 // The . has been scanned.
 func lexField(l *lexer) stateFn {
 	return lexFieldOrVariable(l, itemField)
 }

 // lexVariable scans a Variable: $Alphanumeric.
 // The $ has been scanned.
 func lexVariable(l *lexer) stateFn {
 	if l.atTerminator() { // Nothing interesting follows -> "$".
 		l.emit(itemVariable)
 		return lexInsideAction
 	}
 	return lexFieldOrVariable(l, itemVariable)
 }

 // lexVariable scans a field or variable: [.$]Alphanumeric.
 // The . or $ has been scanned.
 func lexFieldOrVariable(l *lexer, typ itemType) stateFn {
 	if l.atTerminator() { // Nothing interesting follows -> "." or "$".
 		if typ == itemVariable {
 			l.emit(itemVariable)
 		} else {
 			l.emit(itemDot)
 		}
 		return lexInsideAction
 	}
 	var r rune
 	for {
 		r = l.next()
 		if !isAlphaNumeric(r) {
 			l.backup()
 			break
 		}
 	}
 	if !l.atTerminator() {
 		return l.errorf("bad character %#U", r)
 	}
 	l.emit(typ)
 	return lexInsideAction
 }

 // atTerminator reports whether the input is at valid termination character to
 // appear after an identifier. Breaks .X.Y into two pieces. Also catches cases
 // like "$x+2" not being acceptable without a space, in case we decide one
 // day to implement arithmetic.
 func (l *lexer) atTerminator() bool {
 	r := l.peek()
 	if isSpace(r) || isEndOfLine(r) {
 		return true
 	}
 	switch r {
 	case eof, '.', ',', '|', ':', ')', '(':
 		return true
 	}
 	// Does r start the delimiter? This can be ambiguous (with delim=="//", $x/2 will
 	// succeed but should fail) but only in extremely rare cases caused by willfully
 	// bad choice of delimiter.
 	if rd, _ := utf8.DecodeRuneInString(l.rightDelim); rd == r {
 		return true
 	}
 	return false
 }

 // lexChar scans a character constant. The initial quote is already
 // scanned. Syntax checking is done by the parser.
 func lexChar(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 character constant")
 		case '\'':
 			break Loop
 		}
 	}
 	l.emit(itemCharConstant)
 	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 {
 	startLine := l.line
 Loop:
 	for {
 		switch l.next() {
 		case eof:
 			// Restore line number to location of opening quote.
 			// We will error out so it's ok just to overwrite the field.
 			l.line = startLine
 			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 rune) bool {
 	return r == ' ' || r == '\t'
 }

 // isEndOfLine reports whether r is an end-of-line character.
 func isEndOfLine(r rune) bool {
 	return r == '\r' || r == '\n'
 }

 // isAlphaNumeric reports whether r is an alphabetic, digit, or underscore.
 func isAlphaNumeric(r rune) 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 parse

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

	// item represents a token or text string returned from the scanner.
	type item struct {
	typ itemType // The type of this item.
	pos Pos // The starting position, in bytes, of this item in the input string.
	val string // The value of this item.
	line int // The line number at the start of this item.
	}

	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
	itemChar // printable ASCII character; grab bag for comma etc.
	itemCharConstant // character constant
	itemComplex // complex constant (1+2i); imaginary is just a number
	itemColonEquals // colon-equals (':=') introducing a declaration
	itemEOF
	itemField // alphanumeric identifier starting with '.'
	itemIdentifier // alphanumeric identifier not starting with '.'
	itemLeftDelim // left action delimiter
	itemLeftParen // '(' inside action
	itemNumber // simple number, including imaginary
	itemPipe // pipe symbol
	itemRawString // raw quoted string (includes quotes)
	itemRightDelim // right action delimiter
	itemRightParen // ')' inside action
	itemSpace // run of spaces separating arguments
	itemString // quoted string (includes quotes)
	itemText // plain text
	itemVariable // variable starting with '$', such as '$' or '$1' or '$hello'
	// Keywords appear after all the rest.
	itemKeyword // used only to delimit the keywords
	itemBlock // block keyword
	itemDot // the cursor, spelled '.'
	itemDefine // define keyword
	itemElse // else keyword
	itemEnd // end keyword
	itemIf // if keyword
	itemNil // the untyped nil constant, easiest to treat as a keyword
	itemRange // range keyword
	itemTemplate // template keyword
	itemWith // with keyword
	)

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

	const eof = -1

	// Trimming spaces.
	// If the action begins "{{- " rather than "{{", then all space/tab/newlines
	// preceding the action are trimmed; conversely if it ends " -}}" the
	// leading spaces are trimmed. This is done entirely in the lexer; the
	// parser never sees it happen. We require an ASCII space to be
	// present to avoid ambiguity with things like "{{-3}}". It reads
	// better with the space present anyway. For simplicity, only ASCII
	// space does the job.
	const (
	spaceChars = " \t\r\n" // These are the space characters defined by Go itself.
	leftTrimMarker = "- " // Attached to left delimiter, trims trailing spaces from preceding text.
	rightTrimMarker = " -" // Attached to right delimiter, trims leading spaces from following text.
	trimMarkerLen = Pos(len(leftTrimMarker))
	)

	// 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
	leftDelim string // start of action
	rightDelim string // end of action
	state stateFn // the next lexing function to enter
	pos Pos // current position in the input
	start Pos // start position of this item
	width Pos // width of last rune read from input
	lastPos Pos // position of most recent item returned by nextItem
	items chan item // channel of scanned items
	parenDepth int // nesting depth of ( ) exprs
	line int // 1+number of newlines seen
	}

	// next returns the next rune in the input.
	func (l *lexer) next() rune {
	if int(l.pos) >= len(l.input) {
	l.width = 0
	return eof
	}
	r, w := utf8.DecodeRuneInString(l.input[l.pos:])
	l.width = Pos(w)
	l.pos += l.width
	if r == '\n' {
	l.line++
	}
	return r
	}

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

	// backup steps back one rune. Can only be called once per call of next.
	func (l *lexer) backup() {
	l.pos -= l.width
	// Correct newline count.
	if l.width == 1 && l.input[l.pos] == '\n' {
	l.line--
	}
	}

	// emit passes an item back to the client.
	func (l *lexer) emit(t itemType) {
	l.items <- item{t, l.start, l.input[l.start:l.pos], l.line}
	// Some items contain text internally. If so, count their newlines.
	switch t {
	case itemText, itemRawString, itemLeftDelim, itemRightDelim:
	l.line += strings.Count(l.input[l.start:l.pos], "\n")
	}
	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.ContainsRune(valid, l.next()) {
	return true
	}
	l.backup()
	return false
	}

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

	// 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.line}
	return nil
	}

	// nextItem returns the next item from the input.
	// Called by the parser, not in the lexing goroutine.
	func (l *lexer) nextItem() item {
	item := <-l.items
	l.lastPos = item.pos
	return item
	}

	// drain drains the output so the lexing goroutine will exit.
	// Called by the parser, not in the lexing goroutine.
	func (l *lexer) drain() {
	for range l.items {
	}
	}

	// lex creates a new scanner for the input string.
	func lex(name, input, left, right string) *lexer {
	if left == "" {
	left = leftDelim
	}
	if right == "" {
	right = rightDelim
	}
	l := &lexer{
	name: name,
	input: input,
	leftDelim: left,
	rightDelim: right,
	items: make(chan item),
	line: 1,
	}
	go l.run()
	return l
	}

	// run runs the state machine for the lexer.
	func (l *lexer) run() {
	for l.state = lexText; l.state != nil; {
	l.state = l.state(l)
	}
	close(l.items)
	}

	// state functions

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

	// lexText scans until an opening action delimiter, "{{".
	func lexText(l *lexer) stateFn {
	l.width = 0
	if x := strings.Index(l.input[l.pos:], l.leftDelim); x >= 0 {
	ldn := Pos(len(l.leftDelim))
	l.pos += Pos(x)
	trimLength := Pos(0)
	if strings.HasPrefix(l.input[l.pos+ldn:], leftTrimMarker) {
	trimLength = rightTrimLength(l.input[l.start:l.pos])
	}
	l.pos -= trimLength
	if l.pos > l.start {
	l.emit(itemText)
	}
	l.pos += trimLength
	l.ignore()
	return lexLeftDelim
	} else {
	l.pos = Pos(len(l.input))
	}
	// Correctly reached EOF.
	if l.pos > l.start {
	l.emit(itemText)
	}
	l.emit(itemEOF)
	return nil
	}

	// rightTrimLength returns the length of the spaces at the end of the string.
	func rightTrimLength(s string) Pos {
	return Pos(len(s) - len(strings.TrimRight(s, spaceChars)))
	}

	// atRightDelim reports whether the lexer is at a right delimiter, possibly preceded by a trim marker.
	func (l *lexer) atRightDelim() (delim, trimSpaces bool) {
	if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
	return true, false
	}
	// The right delim might have the marker before.
	if strings.HasPrefix(l.input[l.pos:], rightTrimMarker) {
	if strings.HasPrefix(l.input[l.pos+trimMarkerLen:], l.rightDelim) {
	return true, true
	}
	}
	return false, false
	}

	// leftTrimLength returns the length of the spaces at the beginning of the string.
	func leftTrimLength(s string) Pos {
	return Pos(len(s) - len(strings.TrimLeft(s, spaceChars)))
	}

	// lexLeftDelim scans the left delimiter, which is known to be present, possibly with a trim marker.
	func lexLeftDelim(l *lexer) stateFn {
	l.pos += Pos(len(l.leftDelim))
	trimSpace := strings.HasPrefix(l.input[l.pos:], leftTrimMarker)
	afterMarker := Pos(0)
	if trimSpace {
	afterMarker = trimMarkerLen
	}
	if strings.HasPrefix(l.input[l.pos+afterMarker:], leftComment) {
	l.pos += afterMarker
	l.ignore()
	return lexComment
	}
	l.emit(itemLeftDelim)
	l.pos += afterMarker
	l.ignore()
	l.parenDepth = 0
	return lexInsideAction
	}

	// lexComment scans a comment. The left comment marker is known to be present.
	func lexComment(l *lexer) stateFn {
	l.pos += Pos(len(leftComment))
	i := strings.Index(l.input[l.pos:], rightComment)
	if i < 0 {
	return l.errorf("unclosed comment")
	}
	l.pos += Pos(i + len(rightComment))
	delim, trimSpace := l.atRightDelim()
	if !delim {
	return l.errorf("comment ends before closing delimiter")
	}
	if trimSpace {
	l.pos += trimMarkerLen
	}
	l.pos += Pos(len(l.rightDelim))
	if trimSpace {
	l.pos += leftTrimLength(l.input[l.pos:])
	}
	l.ignore()
	return lexText
	}

	// lexRightDelim scans the right delimiter, which is known to be present, possibly with a trim marker.
	func lexRightDelim(l *lexer) stateFn {
	trimSpace := strings.HasPrefix(l.input[l.pos:], rightTrimMarker)
	if trimSpace {
	l.pos += trimMarkerLen
	l.ignore()
	}
	l.pos += Pos(len(l.rightDelim))
	l.emit(itemRightDelim)
	if trimSpace {
	l.pos += leftTrimLength(l.input[l.pos:])
	l.ignore()
	}
	return lexText
	}

	// lexInsideAction scans the elements inside action delimiters.
	func lexInsideAction(l *lexer) stateFn {
	// Either number, quoted string, or identifier.
	// Spaces separate arguments; runs of spaces turn into itemSpace.
	// Pipe symbols separate and are emitted.
	delim, _ := l.atRightDelim()
	if delim {
	if l.parenDepth == 0 {
	return lexRightDelim
	}
	return l.errorf("unclosed left paren")
	}
	switch r := l.next(); {
	case r == eof \|\| isEndOfLine(r):
	return l.errorf("unclosed action")
	case isSpace(r):
	return lexSpace
	case r == ':':
	if l.next() != '=' {
	return l.errorf("expected :=")
	}
	l.emit(itemColonEquals)
	case r == '\|':
	l.emit(itemPipe)
	case r == '"':
	return lexQuote
	case r == '`':
	return lexRawQuote
	case r == '$':
	return lexVariable
	case r == '\'':
	return lexChar
	case r == '.':
	// special look-ahead for ".field" so we don't break l.backup().
	if l.pos < Pos(len(l.input)) {
	r := l.input[l.pos]
	if r < '0' \|\| '9' < r {
	return lexField
	}
	}
	fallthrough // '.' can start a number.
	case r == '+' \|\| r == '-' \|\| ('0' <= r && r <= '9'):
	l.backup()
	return lexNumber
	case isAlphaNumeric(r):
	l.backup()
	return lexIdentifier
	case r == '(':
	l.emit(itemLeftParen)
	l.parenDepth++
	case r == ')':
	l.emit(itemRightParen)
	l.parenDepth--
	if l.parenDepth < 0 {
	return l.errorf("unexpected right paren %#U", r)
	}
	case r <= unicode.MaxASCII && unicode.IsPrint(r):
	l.emit(itemChar)
	return lexInsideAction
	default:
	return l.errorf("unrecognized character in action: %#U", r)
	}
	return lexInsideAction
	}

	// lexSpace scans a run of space characters.
	// One space has already been seen.
	func lexSpace(l *lexer) stateFn {
	for isSpace(l.peek()) {
	l.next()
	}
	l.emit(itemSpace)
	return lexInsideAction
	}

	// lexIdentifier scans an alphanumeric.
	func lexIdentifier(l *lexer) stateFn {
	Loop:
	for {
	switch r := l.next(); {
	case isAlphaNumeric(r):
	// absorb.
	default:
	l.backup()
	word := l.input[l.start:l.pos]
	if !l.atTerminator() {
	return l.errorf("bad character %#U", r)
	}
	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
	}

	// lexField scans a field: .Alphanumeric.
	// The . has been scanned.
	func lexField(l *lexer) stateFn {
	return lexFieldOrVariable(l, itemField)
	}

	// lexVariable scans a Variable: $Alphanumeric.
	// The $ has been scanned.
	func lexVariable(l *lexer) stateFn {
	if l.atTerminator() { // Nothing interesting follows -> "$".
	l.emit(itemVariable)
	return lexInsideAction
	}
	return lexFieldOrVariable(l, itemVariable)
	}

	// lexVariable scans a field or variable: [.$]Alphanumeric.
	// The . or $ has been scanned.
	func lexFieldOrVariable(l *lexer, typ itemType) stateFn {
	if l.atTerminator() { // Nothing interesting follows -> "." or "$".
	if typ == itemVariable {
	l.emit(itemVariable)
	} else {
	l.emit(itemDot)
	}
	return lexInsideAction
	}
	var r rune
	for {
	r = l.next()
	if !isAlphaNumeric(r) {
	l.backup()
	break
	}
	}
	if !l.atTerminator() {
	return l.errorf("bad character %#U", r)
	}
	l.emit(typ)
	return lexInsideAction
	}

	// atTerminator reports whether the input is at valid termination character to
	// appear after an identifier. Breaks .X.Y into two pieces. Also catches cases
	// like "$x+2" not being acceptable without a space, in case we decide one
	// day to implement arithmetic.
	func (l *lexer) atTerminator() bool {
	r := l.peek()
	if isSpace(r) \|\| isEndOfLine(r) {
	return true
	}
	switch r {
	case eof, '.', ',', '\|', ':', ')', '(':
	return true
	}
	// Does r start the delimiter? This can be ambiguous (with delim=="//", $x/2 will
	// succeed but should fail) but only in extremely rare cases caused by willfully
	// bad choice of delimiter.
	if rd, _ := utf8.DecodeRuneInString(l.rightDelim); rd == r {
	return true
	}
	return false
	}

	// lexChar scans a character constant. The initial quote is already
	// scanned. Syntax checking is done by the parser.
	func lexChar(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 character constant")
	case '\'':
	break Loop
	}
	}
	l.emit(itemCharConstant)
	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 {
	startLine := l.line
	Loop:
	for {
	switch l.next() {
	case eof:
	// Restore line number to location of opening quote.
	// We will error out so it's ok just to overwrite the field.
	l.line = startLine
	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 rune) bool {
	return r == ' ' \|\| r == '\t'
	}

	// isEndOfLine reports whether r is an end-of-line character.
	func isEndOfLine(r rune) bool {
	return r == '\r' \|\| r == '\n'
	}

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