Looking forward in the input text without actually stepping the current position.
        returns None if the current position is at the end of the input.

def peek(self, offset=0):
        """ Looking forward in the input text without actually stepping the current position.
        returns None if the current position is at the end of the input. """
        pos = self.pos + offset
        if pos >= self.end:
            return None
        return self.text[pos]