func lexValueSequence(l *lexer) stateFn {
	switch r := l.next(); {
	case r == eof:
		return lexStatements
	case isSpace(r):
		l.emit(ItemSpace)
		lexSpace(l)
	case r == '+':
		l.emit(ItemADD)
	case r == '-':
		l.emit(ItemSUB)
	case r == 'x':
		l.emit(ItemTimes)
	case r == '_':
		l.emit(ItemBlank)
	case isDigit(r) || (r == '.' && isDigit(l.peek())):
		l.backup()
		lexNumber(l)
	case isAlpha(r):
		l.backup()
		// We might lex invalid items here but this will be caught by the parser.
		return lexKeywordOrIdentifier
	default:
		return l.errorf("unexpected character in series sequence: %q", r)
	}
	return lexValueSequence
}
func lexValueSequence(l *lexer) stateFn {
	switch r := l.next(); {
	case r == eof:
		return lexStatements
	case isSpace(r):
		l.emit(ItemSpace)
		lexSpace(l)
	case r == '+':
		l.emit(ItemADD)
	case r == '-':
		l.emit(ItemSUB)
	case r == 'x':
		l.emit(ItemTimes)
	case r == '_':
		l.emit(ItemBlank)
	case isDigit(r) || (r == '.' && isDigit(l.peek())):
		l.backup()
		lexNumber(l)
	case isAlpha(r):
		l.backup()
		// We might lex invalid items here but this will be caught by the parser.
		return lexKeywordOrIdentifier
	default:
		return l.errorf("unexpected character in series sequence: %q", r)
	}
	return lexValueSequence
}
// lexValueSequence scans a value sequence of a series description.