import re


def StrPrefixOf(prefix, input_string):
    """
    Return True if the concrete value of the input_string starts with prefix
    otherwise false.

    :param prefix: prefix we want to check
    :param input_string: the string we want to check

    :return: True if the input_string starts with prefix else false
    """
    return re.match(r'^' + prefix.value, input_string.value) is not None