vendor.conf: pin branches to releases or commits

Most of the dependencies have been copied from libpod's vendor.conf
where such a cleanup has been executed recently.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

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

@@ -3,7 +3,6 @@ package toml
 import (
 	"fmt"
 	"strings"
-	"unicode"
 	"unicode/utf8"
 )
 
@@ -30,28 +29,24 @@ const (
 	itemArrayTableEnd
 	itemKeyStart
 	itemCommentStart
-	itemInlineTableStart
-	itemInlineTableEnd
 )
 
 const (
-	eof              = 0
-	comma            = ','
-	tableStart       = '['
-	tableEnd         = ']'
-	arrayTableStart  = '['
-	arrayTableEnd    = ']'
-	tableSep         = '.'
-	keySep           = '='
-	arrayStart       = '['
-	arrayEnd         = ']'
-	commentStart     = '#'
-	stringStart      = '"'
-	stringEnd        = '"'
-	rawStringStart   = '\''
-	rawStringEnd     = '\''
-	inlineTableStart = '{'
-	inlineTableEnd   = '}'
+	eof             = 0
+	tableStart      = '['
+	tableEnd        = ']'
+	arrayTableStart = '['
+	arrayTableEnd   = ']'
+	tableSep        = '.'
+	keySep          = '='
+	arrayStart      = '['
+	arrayEnd        = ']'
+	arrayValTerm    = ','
+	commentStart    = '#'
+	stringStart     = '"'
+	stringEnd       = '"'
+	rawStringStart  = '\''
+	rawStringEnd    = '\''
 )
 
 type stateFn func(lx *lexer) stateFn
@@ -60,18 +55,11 @@ type lexer struct {
 	input string
 	start int
 	pos   int
+	width 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
@@ -99,7 +87,7 @@ func (lx *lexer) nextItem() item {
 
 func lex(input string) *lexer {
 	lx := &lexer{
-		input: input,
+		input: input + "\n",
 		state: lexTop,
 		line:  1,
 		items: make(chan item, 10),
@@ -114,7 +102,7 @@ func (lx *lexer) push(state stateFn) {
 
 func (lx *lexer) pop() stateFn {
 	if len(lx.stack) == 0 {
-		return lx.errorf("BUG in lexer: no states to pop")
+		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]
@@ -136,25 +124,16 @@ func (lx *lexer) emitTrim(typ itemType) {
 }
 
 func (lx *lexer) next() (r rune) {
-	if lx.atEOF {
-		panic("next called after EOF")
-	}
 	if lx.pos >= len(lx.input) {
-		lx.atEOF = true
+		lx.width = 0
 		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
+	r, lx.width = utf8.DecodeRuneInString(lx.input[lx.pos:])
+	lx.pos += lx.width
 	return r
 }
 
@@ -163,20 +142,9 @@ func (lx *lexer) ignore() {
 	lx.start = lx.pos
 }
 
-// backup steps back one rune. Can be called only twice between calls to next.
+// backup steps back one rune. Can be called only once per call of 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
+	lx.pos -= lx.width
 	if lx.pos < len(lx.input) && lx.input[lx.pos] == '\n' {
 		lx.line--
 	}
@@ -198,22 +166,9 @@ func (lx *lexer) peek() rune {
 	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.).
+// character (new lines, tabs, etc.).
 func (lx *lexer) errorf(format string, values ...interface{}) stateFn {
 	lx.items <- item{
 		itemError,
@@ -229,6 +184,7 @@ func lexTop(lx *lexer) stateFn {
 	if isWhitespace(r) || isNL(r) {
 		return lexSkip(lx, lexTop)
 	}
+
 	switch r {
 	case commentStart:
 		lx.push(lexTop)
@@ -237,7 +193,7 @@ func lexTop(lx *lexer) stateFn {
 		return lexTableStart
 	case eof:
 		if lx.pos > lx.start {
-			return lx.errorf("unexpected EOF")
+			return lx.errorf("Unexpected EOF.")
 		}
 		lx.emit(itemEOF)
 		return nil
@@ -252,12 +208,12 @@ func lexTop(lx *lexer) stateFn {
 
 // 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.
+// upon a new line. 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.
+		// a comment will read to a new line for us.
 		lx.push(lexTop)
 		return lexCommentStart
 	case isWhitespace(r):
@@ -266,11 +222,11 @@ func lexTopEnd(lx *lexer) stateFn {
 		lx.ignore()
 		return lexTop
 	case r == eof:
-		lx.emit(itemEOF)
-		return nil
+		lx.ignore()
+		return lexTop
 	}
-	return lx.errorf("expected a top-level item to end with a newline, "+
-		"comment, or EOF, but got %q instead", r)
+	return lx.errorf("Expected a top-level item to end with a new line, "+
+		"comment or EOF, but got %q instead.", r)
 }
 
 // lexTable lexes the beginning of a table. Namely, it makes sure that
@@ -297,22 +253,21 @@ func lexTableEnd(lx *lexer) stateFn {
 
 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)
+		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)")
+		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)")
+		return lx.errorf("Unexpected table separator. (Table names cannot " +
+			"be empty.)")
 	case r == stringStart || r == rawStringStart:
 		lx.ignore()
 		lx.push(lexTableNameEnd)
@@ -322,22 +277,24 @@ func lexTableNameStart(lx *lexer) stateFn {
 	}
 }
 
-// lexBareTableName lexes the name of a table. It assumes that at least one
+// lexTableName 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) {
+	switch r := lx.next(); {
+	case isBareKeyChar(r):
 		return lexBareTableName
+	case r == tableSep || r == tableEnd:
+		lx.backup()
+		lx.emitTrim(itemText)
+		return lexTableNameEnd
+	default:
+		return lx.errorf("Bare keys cannot contain %q.", r)
 	}
-	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
@@ -347,8 +304,8 @@ func lexTableNameEnd(lx *lexer) stateFn {
 	case r == tableEnd:
 		return lx.pop()
 	default:
-		return lx.errorf("expected '.' or ']' to end table name, "+
-			"but got %q instead", r)
+		return lx.errorf("Expected '.' or ']' to end table name, but got %q "+
+			"instead.", r)
 	}
 }
 
@@ -358,7 +315,7 @@ func lexKeyStart(lx *lexer) stateFn {
 	r := lx.peek()
 	switch {
 	case r == keySep:
-		return lx.errorf("unexpected key separator %q", keySep)
+		return lx.errorf("Unexpected key separator %q.", keySep)
 	case isWhitespace(r) || isNL(r):
 		lx.next()
 		return lexSkip(lx, lexKeyStart)
@@ -381,15 +338,14 @@ func lexBareKey(lx *lexer) stateFn {
 	case isBareKeyChar(r):
 		return lexBareKey
 	case isWhitespace(r):
-		lx.backup()
-		lx.emit(itemText)
+		lx.emitTrim(itemText)
 		return lexKeyEnd
 	case r == keySep:
 		lx.backup()
-		lx.emit(itemText)
+		lx.emitTrim(itemText)
 		return lexKeyEnd
 	default:
-		return lx.errorf("bare keys cannot contain %q", r)
+		return lx.errorf("Bare keys cannot contain %q.", r)
 	}
 }
 
@@ -402,7 +358,7 @@ func lexKeyEnd(lx *lexer) stateFn {
 	case isWhitespace(r):
 		return lexSkip(lx, lexKeyEnd)
 	default:
-		return lx.errorf("expected key separator %q, but got %q instead",
+		return lx.errorf("Expected key separator %q, but got %q instead.",
 			keySep, r)
 	}
 }
@@ -411,26 +367,20 @@ func lexKeyEnd(lx *lexer) stateFn {
 // 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.
+	// We allow whitespace to precede a value, but NOT new lines.
+	// In array syntax, the array states are responsible for ignoring new
+	// lines.
 	r := lx.next()
-	switch {
-	case isWhitespace(r):
+	if 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:
+
+	switch {
+	case r == arrayStart:
 		lx.ignore()
 		lx.emit(itemArray)
 		return lexArrayValue
-	case inlineTableStart:
-		lx.ignore()
-		lx.emit(itemInlineTableStart)
-		return lexInlineTableValue
-	case stringStart:
+	case r == stringStart:
 		if lx.accept(stringStart) {
 			if lx.accept(stringStart) {
 				lx.ignore() // Ignore """
@@ -440,7 +390,7 @@ func lexValue(lx *lexer) stateFn {
 		}
 		lx.ignore() // ignore the '"'
 		return lexString
-	case rawStringStart:
+	case r == rawStringStart:
 		if lx.accept(rawStringStart) {
 			if lx.accept(rawStringStart) {
 				lx.ignore() // Ignore """
@@ -450,24 +400,23 @@ func lexValue(lx *lexer) stateFn {
 		}
 		lx.ignore() // ignore the "'"
 		return lexRawString
-	case '+', '-':
+	case r == 't':
+		return lexTrue
+	case r == 'f':
+		return lexFalse
+	case r == '-':
 		return lexNumberStart
-	case '.': // special error case, be kind to users
-		return lx.errorf("floats must start with a digit, not '.'")
+	case isDigit(r):
+		lx.backup() // avoid an extra state and use the same as above
+		return lexNumberOrDateStart
+	case r == '.': // 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)
+	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.
+// have already been consumed. All whitespace and new lines are ignored.
 func lexArrayValue(lx *lexer) stateFn {
 	r := lx.next()
 	switch {
@@ -476,11 +425,10 @@ func lexArrayValue(lx *lexer) stateFn {
 	case r == commentStart:
 		lx.push(lexArrayValue)
 		return lexCommentStart
-	case r == comma:
-		return lx.errorf("unexpected comma")
+	case r == arrayValTerm:
+		return lx.errorf("Unexpected array value terminator %q.",
+			arrayValTerm)
 	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
 	}
 
@@ -489,9 +437,8 @@ func lexArrayValue(lx *lexer) stateFn {
 	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 ']'.
+// lexArrayValueEnd consumes the cruft between values of an array. Namely,
+// it ignores whitespace and expects either a ',' or a ']'.
 func lexArrayValueEnd(lx *lexer) stateFn {
 	r := lx.next()
 	switch {
@@ -500,88 +447,31 @@ func lexArrayValueEnd(lx *lexer) stateFn {
 	case r == commentStart:
 		lx.push(lexArrayValueEnd)
 		return lexCommentStart
-	case r == comma:
+	case r == arrayValTerm:
 		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,
-	)
+	return lx.errorf("Expected an array value terminator %q or an array "+
+		"terminator %q, but got %q instead.", arrayValTerm, arrayEnd, r)
 }
 
-// lexArrayEnd finishes the lexing of an array.
-// It assumes that a ']' has just been consumed.
+// 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")
+		return lx.errorf("Strings cannot contain new lines.")
 	case r == '\\':
 		lx.push(lexString)
 		return lexStringEscape
@@ -598,12 +488,11 @@ func lexString(lx *lexer) stateFn {
 // 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 '\\':
+	r := lx.next()
+	switch {
+	case r == '\\':
 		return lexMultilineStringEscape
-	case stringEnd:
+	case r == stringEnd:
 		if lx.accept(stringEnd) {
 			if lx.accept(stringEnd) {
 				lx.backup()
@@ -627,10 +516,8 @@ func lexMultilineString(lx *lexer) stateFn {
 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")
+		return lx.errorf("Strings cannot contain new lines.")
 	case r == rawStringEnd:
 		lx.backup()
 		lx.emit(itemRawString)
@@ -642,13 +529,12 @@ func lexRawString(lx *lexer) stateFn {
 }
 
 // lexMultilineRawString consumes a raw string. Nothing can be escaped in such
-// a string. It assumes that the beginning "'''" has already been consumed and
+// 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:
+	r := lx.next()
+	switch {
+	case r == rawStringEnd:
 		if lx.accept(rawStringEnd) {
 			if lx.accept(rawStringEnd) {
 				lx.backup()
@@ -673,10 +559,11 @@ func lexMultilineStringEscape(lx *lexer) stateFn {
 	// Handle the special case first:
 	if isNL(lx.next()) {
 		return lexMultilineString
+	} else {
+		lx.backup()
+		lx.push(lexMultilineString)
+		return lexStringEscape(lx)
 	}
-	lx.backup()
-	lx.push(lexMultilineString)
-	return lexStringEscape(lx)
 }
 
 func lexStringEscape(lx *lexer) stateFn {
@@ -701,9 +588,10 @@ func lexStringEscape(lx *lexer) stateFn {
 	case 'U':
 		return lexLongUnicodeEscape
 	}
-	return lx.errorf("invalid escape character %q; only the following "+
+	return lx.errorf("Invalid escape character %q. Only the following "+
 		"escape characters are allowed: "+
-		`\b, \t, \n, \f, \r, \", \\, \uXXXX, and \UXXXXXXXX`, r)
+		"\\b, \\t, \\n, \\f, \\r, \\\", \\/, \\\\, "+
+		"\\uXXXX and \\UXXXXXXXX.", r)
 }
 
 func lexShortUnicodeEscape(lx *lexer) stateFn {
@@ -711,8 +599,8 @@ func lexShortUnicodeEscape(lx *lexer) stateFn {
 	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.errorf("Expected four hexadecimal digits after '\\u', "+
+				"but got '%s' instead.", lx.current())
 		}
 	}
 	return lx.pop()
@@ -723,43 +611,40 @@ func lexLongUnicodeEscape(lx *lexer) stateFn {
 	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.errorf("Expected eight hexadecimal digits after '\\U', "+
+				"but got '%s' instead.", lx.current())
 		}
 	}
 	return lx.pop()
 }
 
-// lexNumberOrDateStart consumes either an integer, a float, or datetime.
+// lexNumberOrDateStart consumes either a (positive) integer, float or
+// datetime. It assumes that NO negative sign has been consumed.
 func lexNumberOrDateStart(lx *lexer) stateFn {
 	r := lx.next()
-	if isDigit(r) {
-		return lexNumberOrDate
+	if !isDigit(r) {
+		if r == '.' {
+			return lx.errorf("Floats must start with a digit, not '.'.")
+		} else {
+			return lx.errorf("Expected a digit but got %q.", r)
+		}
 	}
-	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)
+	return lexNumberOrDate
 }
 
-// lexNumberOrDate consumes either an integer, float or datetime.
+// lexNumberOrDate consumes either a (positive) integer, float or datetime.
 func lexNumberOrDate(lx *lexer) stateFn {
 	r := lx.next()
-	if isDigit(r) {
+	switch {
+	case r == '-':
+		if lx.pos-lx.start != 5 {
+			return lx.errorf("All ISO8601 dates must be in full Zulu form.")
+		}
+		return lexDateAfterYear
+	case isDigit(r):
 		return lexNumberOrDate
-	}
-	switch r {
-	case '-':
-		return lexDatetime
-	case '_':
-		return lexNumber
-	case '.', 'e', 'E':
-		return lexFloat
+	case r == '.':
+		return lexFloatStart
 	}
 
 	lx.backup()
@@ -767,34 +652,46 @@ func lexNumberOrDate(lx *lexer) stateFn {
 	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
+// lexDateAfterYear consumes a full Zulu Datetime in ISO8601 format.
+// It assumes that "YYYY-" has already been consumed.
+func lexDateAfterYear(lx *lexer) stateFn {
+	formats := []rune{
+		// digits are '0'.
+		// everything else is direct equality.
+		'0', '0', '-', '0', '0',
+		'T',
+		'0', '0', ':', '0', '0', ':', '0', '0',
+		'Z',
 	}
-	switch r {
-	case '-', 'T', ':', '.', 'Z', '+':
-		return lexDatetime
+	for _, f := range formats {
+		r := lx.next()
+		if f == '0' {
+			if !isDigit(r) {
+				return lx.errorf("Expected digit in ISO8601 datetime, "+
+					"but found %q instead.", r)
+			}
+		} else if f != r {
+			return lx.errorf("Expected %q in ISO8601 datetime, "+
+				"but found %q instead.", f, r)
+		}
 	}
-
-	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.
+// lexNumberStart consumes either an integer or a float. It assumes that
+// a negative 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.
+	// 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("Floats must start with a digit, not '.'.")
+		} else {
+			return lx.errorf("Expected a digit but got %q.", r)
 		}
-		return lx.errorf("expected a digit but got %q", r)
 	}
 	return lexNumber
 }
@@ -802,14 +699,11 @@ func lexNumberStart(lx *lexer) stateFn {
 // lexNumber consumes an integer or a float after seeing the first digit.
 func lexNumber(lx *lexer) stateFn {
 	r := lx.next()
-	if isDigit(r) {
+	switch {
+	case isDigit(r):
 		return lexNumber
-	}
-	switch r {
-	case '_':
-		return lexNumber
-	case '.', 'e', 'E':
-		return lexFloat
+	case r == '.':
+		return lexFloatStart
 	}
 
 	lx.backup()
@@ -817,42 +711,60 @@ func lexNumber(lx *lexer) stateFn {
 	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.
+// lexFloatStart starts the consumption of digits of a float after a '.'.
+// Namely, at least one digit is required.
+func lexFloatStart(lx *lexer) stateFn {
+	r := lx.next()
+	if !isDigit(r) {
+		return lx.errorf("Floats must have a digit after the '.', but got "+
+			"%q instead.", r)
+	}
+	return lexFloat
+}
+
+// lexFloat consumes the digits of a float after a '.'.
+// Assumes that one digit has been consumed after a '.' already.
 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
+// lexConst consumes the s[1:] in s. It assumes that s[0] has already been
+// consumed.
+func lexConst(lx *lexer, s string) stateFn {
+	for i := range s[1:] {
+		if r := lx.next(); r != rune(s[i+1]) {
+			return lx.errorf("Expected %q, but found %q instead.", s[:i+1],
+				s[:i]+string(r))
 		}
-		rs = append(rs, r)
 	}
-	s := string(rs)
-	switch s {
-	case "true", "false":
-		lx.emit(itemBool)
-		return lx.pop()
+	return nil
+}
+
+// lexTrue consumes the "rue" in "true". It assumes that 't' has already
+// been consumed.
+func lexTrue(lx *lexer) stateFn {
+	if fn := lexConst(lx, "true"); fn != nil {
+		return fn
 	}
-	return lx.errorf("expected value but found %q instead", s)
+	lx.emit(itemBool)
+	return lx.pop()
+}
+
+// lexFalse consumes the "alse" in "false". It assumes that 'f' has already
+// been consumed.
+func lexFalse(lx *lexer) stateFn {
+	if fn := lexConst(lx, "false"); fn != nil {
+		return fn
+	}
+	lx.emit(itemBool)
+	return lx.pop()
 }
 
 // lexCommentStart begins the lexing of a comment. It will emit
@@ -864,7 +776,7 @@ func lexCommentStart(lx *lexer) stateFn {
 }
 
 // lexComment lexes an entire comment. It assumes that '#' has been consumed.
-// It will consume *up to* the first newline character, and pass control
+// It will consume *up to* the first new line character, and pass control
 // back to the last state on the stack.
 func lexComment(lx *lexer) stateFn {
 	r := lx.peek()
@@ -922,7 +834,13 @@ func (itype itemType) String() string {
 		return "EOF"
 	case itemText:
 		return "Text"
-	case itemString, itemRawString, itemMultilineString, itemRawMultilineString:
+	case itemString:
+		return "String"
+	case itemRawString:
+		return "String"
+	case itemMultilineString:
+		return "String"
+	case itemRawMultilineString:
 		return "String"
 	case itemBool:
 		return "Bool"