Switch from glide to dep. Check in vendor/

vendor/github.com/BurntSushi/toml/lex.go

@@ -0,0 +1,953 @@
+package toml
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+type itemType int
+
+const (
+	itemError itemType = iota
+	itemNIL            // used in the parser to indicate no type
+	itemEOF
+	itemText
+	itemString
+	itemRawString
+	itemMultilineString
+	itemRawMultilineString
+	itemBool
+	itemInteger
+	itemFloat
+	itemDatetime
+	itemArray // the start of an array
+	itemArrayEnd
+	itemTableStart
+	itemTableEnd
+	itemArrayTableStart
+	itemArrayTableEnd
+	itemKeyStart
+	itemCommentStart
+	itemInlineTableStart
+	itemInlineTableEnd
+)
+
+const (
+	eof              = 0
+	comma            = ','
+	tableStart       = '['
+	tableEnd         = ']'
+	arrayTableStart  = '['
+	arrayTableEnd    = ']'
+	tableSep         = '.'
+	keySep           = '='
+	arrayStart       = '['
+	arrayEnd         = ']'
+	commentStart     = '#'
+	stringStart      = '"'
+	stringEnd        = '"'
+	rawStringStart   = '\''
+	rawStringEnd     = '\''
+	inlineTableStart = '{'
+	inlineTableEnd   = '}'
+)
+
+type stateFn func(lx *lexer) stateFn
+
+type lexer struct {
+	input string
+	start int
+	pos   int
+	line  int
+	state stateFn
+	items chan item
+
+	// Allow for backing up up to three runes.
+	// This is necessary because TOML contains 3-rune tokens (""" and ''').
+	prevWidths [3]int
+	nprev      int // how many of prevWidths are in use
+	// If we emit an eof, we can still back up, but it is not OK to call
+	// next again.
+	atEOF bool
+
+	// A stack of state functions used to maintain context.
+	// The idea is to reuse parts of the state machine in various places.
+	// For example, values can appear at the top level or within arbitrarily
+	// nested arrays. The last state on the stack is used after a value has
+	// been lexed. Similarly for comments.
+	stack []stateFn
+}
+
+type item struct {
+	typ  itemType
+	val  string
+	line int
+}
+
+func (lx *lexer) nextItem() item {
+	for {
+		select {
+		case item := <-lx.items:
+			return item
+		default:
+			lx.state = lx.state(lx)
+		}
+	}
+}
+
+func lex(input string) *lexer {
+	lx := &lexer{
+		input: input,
+		state: lexTop,
+		line:  1,
+		items: make(chan item, 10),
+		stack: make([]stateFn, 0, 10),
+	}
+	return lx
+}
+
+func (lx *lexer) push(state stateFn) {
+	lx.stack = append(lx.stack, state)
+}
+
+func (lx *lexer) pop() stateFn {
+	if len(lx.stack) == 0 {
+		return lx.errorf("BUG in lexer: no states to pop")
+	}
+	last := lx.stack[len(lx.stack)-1]
+	lx.stack = lx.stack[0 : len(lx.stack)-1]
+	return last
+}
+
+func (lx *lexer) current() string {
+	return lx.input[lx.start:lx.pos]
+}
+
+func (lx *lexer) emit(typ itemType) {
+	lx.items <- item{typ, lx.current(), lx.line}
+	lx.start = lx.pos
+}
+
+func (lx *lexer) emitTrim(typ itemType) {
+	lx.items <- item{typ, strings.TrimSpace(lx.current()), lx.line}
+	lx.start = lx.pos
+}
+
+func (lx *lexer) next() (r rune) {
+	if lx.atEOF {
+		panic("next called after EOF")
+	}
+	if lx.pos >= len(lx.input) {
+		lx.atEOF = true
+		return eof
+	}
+
+	if lx.input[lx.pos] == '\n' {
+		lx.line++
+	}
+	lx.prevWidths[2] = lx.prevWidths[1]
+	lx.prevWidths[1] = lx.prevWidths[0]
+	if lx.nprev < 3 {
+		lx.nprev++
+	}
+	r, w := utf8.DecodeRuneInString(lx.input[lx.pos:])
+	lx.prevWidths[0] = w
+	lx.pos += w
+	return r
+}
+
+// ignore skips over the pending input before this point.
+func (lx *lexer) ignore() {
+	lx.start = lx.pos
+}
+
+// backup steps back one rune. Can be called only twice between calls to next.
+func (lx *lexer) backup() {
+	if lx.atEOF {
+		lx.atEOF = false
+		return
+	}
+	if lx.nprev < 1 {
+		panic("backed up too far")
+	}
+	w := lx.prevWidths[0]
+	lx.prevWidths[0] = lx.prevWidths[1]
+	lx.prevWidths[1] = lx.prevWidths[2]
+	lx.nprev--
+	lx.pos -= w
+	if lx.pos < len(lx.input) && lx.input[lx.pos] == '\n' {
+		lx.line--
+	}
+}
+
+// accept consumes the next rune if it's equal to `valid`.
+func (lx *lexer) accept(valid rune) bool {
+	if lx.next() == valid {
+		return true
+	}
+	lx.backup()
+	return false
+}
+
+// peek returns but does not consume the next rune in the input.
+func (lx *lexer) peek() rune {
+	r := lx.next()
+	lx.backup()
+	return r
+}
+
+// skip ignores all input that matches the given predicate.
+func (lx *lexer) skip(pred func(rune) bool) {
+	for {
+		r := lx.next()
+		if pred(r) {
+			continue
+		}
+		lx.backup()
+		lx.ignore()
+		return
+	}
+}
+
+// errorf stops all lexing by emitting an error and returning `nil`.
+// Note that any value that is a character is escaped if it's a special
+// character (newlines, tabs, etc.).
+func (lx *lexer) errorf(format string, values ...interface{}) stateFn {
+	lx.items <- item{
+		itemError,
+		fmt.Sprintf(format, values...),
+		lx.line,
+	}
+	return nil
+}
+
+// lexTop consumes elements at the top level of TOML data.
+func lexTop(lx *lexer) stateFn {
+	r := lx.next()
+	if isWhitespace(r) || isNL(r) {
+		return lexSkip(lx, lexTop)
+	}
+	switch r {
+	case commentStart:
+		lx.push(lexTop)
+		return lexCommentStart
+	case tableStart:
+		return lexTableStart
+	case eof:
+		if lx.pos > lx.start {
+			return lx.errorf("unexpected EOF")
+		}
+		lx.emit(itemEOF)
+		return nil
+	}
+
+	// At this point, the only valid item can be a key, so we back up
+	// and let the key lexer do the rest.
+	lx.backup()
+	lx.push(lexTopEnd)
+	return lexKeyStart
+}
+
+// lexTopEnd is entered whenever a top-level item has been consumed. (A value
+// or a table.) It must see only whitespace, and will turn back to lexTop
+// upon a newline. If it sees EOF, it will quit the lexer successfully.
+func lexTopEnd(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case r == commentStart:
+		// a comment will read to a newline for us.
+		lx.push(lexTop)
+		return lexCommentStart
+	case isWhitespace(r):
+		return lexTopEnd
+	case isNL(r):
+		lx.ignore()
+		return lexTop
+	case r == eof:
+		lx.emit(itemEOF)
+		return nil
+	}
+	return lx.errorf("expected a top-level item to end with a newline, "+
+		"comment, or EOF, but got %q instead", r)
+}
+
+// lexTable lexes the beginning of a table. Namely, it makes sure that
+// it starts with a character other than '.' and ']'.
+// It assumes that '[' has already been consumed.
+// It also handles the case that this is an item in an array of tables.
+// e.g., '[[name]]'.
+func lexTableStart(lx *lexer) stateFn {
+	if lx.peek() == arrayTableStart {
+		lx.next()
+		lx.emit(itemArrayTableStart)
+		lx.push(lexArrayTableEnd)
+	} else {
+		lx.emit(itemTableStart)
+		lx.push(lexTableEnd)
+	}
+	return lexTableNameStart
+}
+
+func lexTableEnd(lx *lexer) stateFn {
+	lx.emit(itemTableEnd)
+	return lexTopEnd
+}
+
+func lexArrayTableEnd(lx *lexer) stateFn {
+	if r := lx.next(); r != arrayTableEnd {
+		return lx.errorf("expected end of table array name delimiter %q, "+
+			"but got %q instead", arrayTableEnd, r)
+	}
+	lx.emit(itemArrayTableEnd)
+	return lexTopEnd
+}
+
+func lexTableNameStart(lx *lexer) stateFn {
+	lx.skip(isWhitespace)
+	switch r := lx.peek(); {
+	case r == tableEnd || r == eof:
+		return lx.errorf("unexpected end of table name " +
+			"(table names cannot be empty)")
+	case r == tableSep:
+		return lx.errorf("unexpected table separator " +
+			"(table names cannot be empty)")
+	case r == stringStart || r == rawStringStart:
+		lx.ignore()
+		lx.push(lexTableNameEnd)
+		return lexValue // reuse string lexing
+	default:
+		return lexBareTableName
+	}
+}
+
+// lexBareTableName lexes the name of a table. It assumes that at least one
+// valid character for the table has already been read.
+func lexBareTableName(lx *lexer) stateFn {
+	r := lx.next()
+	if isBareKeyChar(r) {
+		return lexBareTableName
+	}
+	lx.backup()
+	lx.emit(itemText)
+	return lexTableNameEnd
+}
+
+// lexTableNameEnd reads the end of a piece of a table name, optionally
+// consuming whitespace.
+func lexTableNameEnd(lx *lexer) stateFn {
+	lx.skip(isWhitespace)
+	switch r := lx.next(); {
+	case isWhitespace(r):
+		return lexTableNameEnd
+	case r == tableSep:
+		lx.ignore()
+		return lexTableNameStart
+	case r == tableEnd:
+		return lx.pop()
+	default:
+		return lx.errorf("expected '.' or ']' to end table name, "+
+			"but got %q instead", r)
+	}
+}
+
+// lexKeyStart consumes a key name up until the first non-whitespace character.
+// lexKeyStart will ignore whitespace.
+func lexKeyStart(lx *lexer) stateFn {
+	r := lx.peek()
+	switch {
+	case r == keySep:
+		return lx.errorf("unexpected key separator %q", keySep)
+	case isWhitespace(r) || isNL(r):
+		lx.next()
+		return lexSkip(lx, lexKeyStart)
+	case r == stringStart || r == rawStringStart:
+		lx.ignore()
+		lx.emit(itemKeyStart)
+		lx.push(lexKeyEnd)
+		return lexValue // reuse string lexing
+	default:
+		lx.ignore()
+		lx.emit(itemKeyStart)
+		return lexBareKey
+	}
+}
+
+// lexBareKey consumes the text of a bare key. Assumes that the first character
+// (which is not whitespace) has not yet been consumed.
+func lexBareKey(lx *lexer) stateFn {
+	switch r := lx.next(); {
+	case isBareKeyChar(r):
+		return lexBareKey
+	case isWhitespace(r):
+		lx.backup()
+		lx.emit(itemText)
+		return lexKeyEnd
+	case r == keySep:
+		lx.backup()
+		lx.emit(itemText)
+		return lexKeyEnd
+	default:
+		return lx.errorf("bare keys cannot contain %q", r)
+	}
+}
+
+// lexKeyEnd consumes the end of a key and trims whitespace (up to the key
+// separator).
+func lexKeyEnd(lx *lexer) stateFn {
+	switch r := lx.next(); {
+	case r == keySep:
+		return lexSkip(lx, lexValue)
+	case isWhitespace(r):
+		return lexSkip(lx, lexKeyEnd)
+	default:
+		return lx.errorf("expected key separator %q, but got %q instead",
+			keySep, r)
+	}
+}
+
+// lexValue starts the consumption of a value anywhere a value is expected.
+// lexValue will ignore whitespace.
+// After a value is lexed, the last state on the next is popped and returned.
+func lexValue(lx *lexer) stateFn {
+	// We allow whitespace to precede a value, but NOT newlines.
+	// In array syntax, the array states are responsible for ignoring newlines.
+	r := lx.next()
+	switch {
+	case isWhitespace(r):
+		return lexSkip(lx, lexValue)
+	case isDigit(r):
+		lx.backup() // avoid an extra state and use the same as above
+		return lexNumberOrDateStart
+	}
+	switch r {
+	case arrayStart:
+		lx.ignore()
+		lx.emit(itemArray)
+		return lexArrayValue
+	case inlineTableStart:
+		lx.ignore()
+		lx.emit(itemInlineTableStart)
+		return lexInlineTableValue
+	case stringStart:
+		if lx.accept(stringStart) {
+			if lx.accept(stringStart) {
+				lx.ignore() // Ignore """
+				return lexMultilineString
+			}
+			lx.backup()
+		}
+		lx.ignore() // ignore the '"'
+		return lexString
+	case rawStringStart:
+		if lx.accept(rawStringStart) {
+			if lx.accept(rawStringStart) {
+				lx.ignore() // Ignore """
+				return lexMultilineRawString
+			}
+			lx.backup()
+		}
+		lx.ignore() // ignore the "'"
+		return lexRawString
+	case '+', '-':
+		return lexNumberStart
+	case '.': // special error case, be kind to users
+		return lx.errorf("floats must start with a digit, not '.'")
+	}
+	if unicode.IsLetter(r) {
+		// Be permissive here; lexBool will give a nice error if the
+		// user wrote something like
+		//   x = foo
+		// (i.e. not 'true' or 'false' but is something else word-like.)
+		lx.backup()
+		return lexBool
+	}
+	return lx.errorf("expected value but found %q instead", r)
+}
+
+// lexArrayValue consumes one value in an array. It assumes that '[' or ','
+// have already been consumed. All whitespace and newlines are ignored.
+func lexArrayValue(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case isWhitespace(r) || isNL(r):
+		return lexSkip(lx, lexArrayValue)
+	case r == commentStart:
+		lx.push(lexArrayValue)
+		return lexCommentStart
+	case r == comma:
+		return lx.errorf("unexpected comma")
+	case r == arrayEnd:
+		// NOTE(caleb): The spec isn't clear about whether you can have
+		// a trailing comma or not, so we'll allow it.
+		return lexArrayEnd
+	}
+
+	lx.backup()
+	lx.push(lexArrayValueEnd)
+	return lexValue
+}
+
+// lexArrayValueEnd consumes everything between the end of an array value and
+// the next value (or the end of the array): it ignores whitespace and newlines
+// and expects either a ',' or a ']'.
+func lexArrayValueEnd(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case isWhitespace(r) || isNL(r):
+		return lexSkip(lx, lexArrayValueEnd)
+	case r == commentStart:
+		lx.push(lexArrayValueEnd)
+		return lexCommentStart
+	case r == comma:
+		lx.ignore()
+		return lexArrayValue // move on to the next value
+	case r == arrayEnd:
+		return lexArrayEnd
+	}
+	return lx.errorf(
+		"expected a comma or array terminator %q, but got %q instead",
+		arrayEnd, r,
+	)
+}
+
+// lexArrayEnd finishes the lexing of an array.
+// It assumes that a ']' has just been consumed.
+func lexArrayEnd(lx *lexer) stateFn {
+	lx.ignore()
+	lx.emit(itemArrayEnd)
+	return lx.pop()
+}
+
+// lexInlineTableValue consumes one key/value pair in an inline table.
+// It assumes that '{' or ',' have already been consumed. Whitespace is ignored.
+func lexInlineTableValue(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case isWhitespace(r):
+		return lexSkip(lx, lexInlineTableValue)
+	case isNL(r):
+		return lx.errorf("newlines not allowed within inline tables")
+	case r == commentStart:
+		lx.push(lexInlineTableValue)
+		return lexCommentStart
+	case r == comma:
+		return lx.errorf("unexpected comma")
+	case r == inlineTableEnd:
+		return lexInlineTableEnd
+	}
+	lx.backup()
+	lx.push(lexInlineTableValueEnd)
+	return lexKeyStart
+}
+
+// lexInlineTableValueEnd consumes everything between the end of an inline table
+// key/value pair and the next pair (or the end of the table):
+// it ignores whitespace and expects either a ',' or a '}'.
+func lexInlineTableValueEnd(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case isWhitespace(r):
+		return lexSkip(lx, lexInlineTableValueEnd)
+	case isNL(r):
+		return lx.errorf("newlines not allowed within inline tables")
+	case r == commentStart:
+		lx.push(lexInlineTableValueEnd)
+		return lexCommentStart
+	case r == comma:
+		lx.ignore()
+		return lexInlineTableValue
+	case r == inlineTableEnd:
+		return lexInlineTableEnd
+	}
+	return lx.errorf("expected a comma or an inline table terminator %q, "+
+		"but got %q instead", inlineTableEnd, r)
+}
+
+// lexInlineTableEnd finishes the lexing of an inline table.
+// It assumes that a '}' has just been consumed.
+func lexInlineTableEnd(lx *lexer) stateFn {
+	lx.ignore()
+	lx.emit(itemInlineTableEnd)
+	return lx.pop()
+}
+
+// lexString consumes the inner contents of a string. It assumes that the
+// beginning '"' has already been consumed and ignored.
+func lexString(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case r == eof:
+		return lx.errorf("unexpected EOF")
+	case isNL(r):
+		return lx.errorf("strings cannot contain newlines")
+	case r == '\\':
+		lx.push(lexString)
+		return lexStringEscape
+	case r == stringEnd:
+		lx.backup()
+		lx.emit(itemString)
+		lx.next()
+		lx.ignore()
+		return lx.pop()
+	}
+	return lexString
+}
+
+// lexMultilineString consumes the inner contents of a string. It assumes that
+// the beginning '"""' has already been consumed and ignored.
+func lexMultilineString(lx *lexer) stateFn {
+	switch lx.next() {
+	case eof:
+		return lx.errorf("unexpected EOF")
+	case '\\':
+		return lexMultilineStringEscape
+	case stringEnd:
+		if lx.accept(stringEnd) {
+			if lx.accept(stringEnd) {
+				lx.backup()
+				lx.backup()
+				lx.backup()
+				lx.emit(itemMultilineString)
+				lx.next()
+				lx.next()
+				lx.next()
+				lx.ignore()
+				return lx.pop()
+			}
+			lx.backup()
+		}
+	}
+	return lexMultilineString
+}
+
+// lexRawString consumes a raw string. Nothing can be escaped in such a string.
+// It assumes that the beginning "'" has already been consumed and ignored.
+func lexRawString(lx *lexer) stateFn {
+	r := lx.next()
+	switch {
+	case r == eof:
+		return lx.errorf("unexpected EOF")
+	case isNL(r):
+		return lx.errorf("strings cannot contain newlines")
+	case r == rawStringEnd:
+		lx.backup()
+		lx.emit(itemRawString)
+		lx.next()
+		lx.ignore()
+		return lx.pop()
+	}
+	return lexRawString
+}
+
+// lexMultilineRawString consumes a raw string. Nothing can be escaped in such
+// a string. It assumes that the beginning "'''" has already been consumed and
+// ignored.
+func lexMultilineRawString(lx *lexer) stateFn {
+	switch lx.next() {
+	case eof:
+		return lx.errorf("unexpected EOF")
+	case rawStringEnd:
+		if lx.accept(rawStringEnd) {
+			if lx.accept(rawStringEnd) {
+				lx.backup()
+				lx.backup()
+				lx.backup()
+				lx.emit(itemRawMultilineString)
+				lx.next()
+				lx.next()
+				lx.next()
+				lx.ignore()
+				return lx.pop()
+			}
+			lx.backup()
+		}
+	}
+	return lexMultilineRawString
+}
+
+// lexMultilineStringEscape consumes an escaped character. It assumes that the
+// preceding '\\' has already been consumed.
+func lexMultilineStringEscape(lx *lexer) stateFn {
+	// Handle the special case first:
+	if isNL(lx.next()) {
+		return lexMultilineString
+	}
+	lx.backup()
+	lx.push(lexMultilineString)
+	return lexStringEscape(lx)
+}
+
+func lexStringEscape(lx *lexer) stateFn {
+	r := lx.next()
+	switch r {
+	case 'b':
+		fallthrough
+	case 't':
+		fallthrough
+	case 'n':
+		fallthrough
+	case 'f':
+		fallthrough
+	case 'r':
+		fallthrough
+	case '"':
+		fallthrough
+	case '\\':
+		return lx.pop()
+	case 'u':
+		return lexShortUnicodeEscape
+	case 'U':
+		return lexLongUnicodeEscape
+	}
+	return lx.errorf("invalid escape character %q; only the following "+
+		"escape characters are allowed: "+
+		`\b, \t, \n, \f, \r, \", \\, \uXXXX, and \UXXXXXXXX`, r)
+}
+
+func lexShortUnicodeEscape(lx *lexer) stateFn {
+	var r rune
+	for i := 0; i < 4; i++ {
+		r = lx.next()
+		if !isHexadecimal(r) {
+			return lx.errorf(`expected four hexadecimal digits after '\u', `+
+				"but got %q instead", lx.current())
+		}
+	}
+	return lx.pop()
+}
+
+func lexLongUnicodeEscape(lx *lexer) stateFn {
+	var r rune
+	for i := 0; i < 8; i++ {
+		r = lx.next()
+		if !isHexadecimal(r) {
+			return lx.errorf(`expected eight hexadecimal digits after '\U', `+
+				"but got %q instead", lx.current())
+		}
+	}
+	return lx.pop()
+}
+
+// lexNumberOrDateStart consumes either an integer, a float, or datetime.
+func lexNumberOrDateStart(lx *lexer) stateFn {
+	r := lx.next()
+	if isDigit(r) {
+		return lexNumberOrDate
+	}
+	switch r {
+	case '_':
+		return lexNumber
+	case 'e', 'E':
+		return lexFloat
+	case '.':
+		return lx.errorf("floats must start with a digit, not '.'")
+	}
+	return lx.errorf("expected a digit but got %q", r)
+}
+
+// lexNumberOrDate consumes either an integer, float or datetime.
+func lexNumberOrDate(lx *lexer) stateFn {
+	r := lx.next()
+	if isDigit(r) {
+		return lexNumberOrDate
+	}
+	switch r {
+	case '-':
+		return lexDatetime
+	case '_':
+		return lexNumber
+	case '.', 'e', 'E':
+		return lexFloat
+	}
+
+	lx.backup()
+	lx.emit(itemInteger)
+	return lx.pop()
+}
+
+// lexDatetime consumes a Datetime, to a first approximation.
+// The parser validates that it matches one of the accepted formats.
+func lexDatetime(lx *lexer) stateFn {
+	r := lx.next()
+	if isDigit(r) {
+		return lexDatetime
+	}
+	switch r {
+	case '-', 'T', ':', '.', 'Z':
+		return lexDatetime
+	}
+
+	lx.backup()
+	lx.emit(itemDatetime)
+	return lx.pop()
+}
+
+// lexNumberStart consumes either an integer or a float. It assumes that a sign
+// has already been read, but that *no* digits have been consumed.
+// lexNumberStart will move to the appropriate integer or float states.
+func lexNumberStart(lx *lexer) stateFn {
+	// We MUST see a digit. Even floats have to start with a digit.
+	r := lx.next()
+	if !isDigit(r) {
+		if r == '.' {
+			return lx.errorf("floats must start with a digit, not '.'")
+		}
+		return lx.errorf("expected a digit but got %q", r)
+	}
+	return lexNumber
+}
+
+// lexNumber consumes an integer or a float after seeing the first digit.
+func lexNumber(lx *lexer) stateFn {
+	r := lx.next()
+	if isDigit(r) {
+		return lexNumber
+	}
+	switch r {
+	case '_':
+		return lexNumber
+	case '.', 'e', 'E':
+		return lexFloat
+	}
+
+	lx.backup()
+	lx.emit(itemInteger)
+	return lx.pop()
+}
+
+// lexFloat consumes the elements of a float. It allows any sequence of
+// float-like characters, so floats emitted by the lexer are only a first
+// approximation and must be validated by the parser.
+func lexFloat(lx *lexer) stateFn {
+	r := lx.next()
+	if isDigit(r) {
+		return lexFloat
+	}
+	switch r {
+	case '_', '.', '-', '+', 'e', 'E':
+		return lexFloat
+	}
+
+	lx.backup()
+	lx.emit(itemFloat)
+	return lx.pop()
+}
+
+// lexBool consumes a bool string: 'true' or 'false.
+func lexBool(lx *lexer) stateFn {
+	var rs []rune
+	for {
+		r := lx.next()
+		if !unicode.IsLetter(r) {
+			lx.backup()
+			break
+		}
+		rs = append(rs, r)
+	}
+	s := string(rs)
+	switch s {
+	case "true", "false":
+		lx.emit(itemBool)
+		return lx.pop()
+	}
+	return lx.errorf("expected value but found %q instead", s)
+}
+
+// lexCommentStart begins the lexing of a comment. It will emit
+// itemCommentStart and consume no characters, passing control to lexComment.
+func lexCommentStart(lx *lexer) stateFn {
+	lx.ignore()
+	lx.emit(itemCommentStart)
+	return lexComment
+}
+
+// lexComment lexes an entire comment. It assumes that '#' has been consumed.
+// It will consume *up to* the first newline character, and pass control
+// back to the last state on the stack.
+func lexComment(lx *lexer) stateFn {
+	r := lx.peek()
+	if isNL(r) || r == eof {
+		lx.emit(itemText)
+		return lx.pop()
+	}
+	lx.next()
+	return lexComment
+}
+
+// lexSkip ignores all slurped input and moves on to the next state.
+func lexSkip(lx *lexer, nextState stateFn) stateFn {
+	return func(lx *lexer) stateFn {
+		lx.ignore()
+		return nextState
+	}
+}
+
+// isWhitespace returns true if `r` is a whitespace character according
+// to the spec.
+func isWhitespace(r rune) bool {
+	return r == '\t' || r == ' '
+}
+
+func isNL(r rune) bool {
+	return r == '\n' || r == '\r'
+}
+
+func isDigit(r rune) bool {
+	return r >= '0' && r <= '9'
+}
+
+func isHexadecimal(r rune) bool {
+	return (r >= '0' && r <= '9') ||
+		(r >= 'a' && r <= 'f') ||
+		(r >= 'A' && r <= 'F')
+}
+
+func isBareKeyChar(r rune) bool {
+	return (r >= 'A' && r <= 'Z') ||
+		(r >= 'a' && r <= 'z') ||
+		(r >= '0' && r <= '9') ||
+		r == '_' ||
+		r == '-'
+}
+
+func (itype itemType) String() string {
+	switch itype {
+	case itemError:
+		return "Error"
+	case itemNIL:
+		return "NIL"
+	case itemEOF:
+		return "EOF"
+	case itemText:
+		return "Text"
+	case itemString, itemRawString, itemMultilineString, itemRawMultilineString:
+		return "String"
+	case itemBool:
+		return "Bool"
+	case itemInteger:
+		return "Integer"
+	case itemFloat:
+		return "Float"
+	case itemDatetime:
+		return "DateTime"
+	case itemTableStart:
+		return "TableStart"
+	case itemTableEnd:
+		return "TableEnd"
+	case itemKeyStart:
+		return "KeyStart"
+	case itemArray:
+		return "Array"
+	case itemArrayEnd:
+		return "ArrayEnd"
+	case itemCommentStart:
+		return "CommentStart"
+	}
+	panic(fmt.Sprintf("BUG: Unknown type '%d'.", int(itype)))
+}
+
+func (item item) String() string {
+	return fmt.Sprintf("(%s, %s)", item.typ.String(), item.val)
+}