def StrPrefixOf(prefix, input_string):
return re.match(r'<STR_LIT>' + prefix.value, input_string.value) is not None<EOL>
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