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