gistfile1.py

#!/usr/bin/env python
# -*- coding: utf8 -*-

# T → g(b|c)d

import sys


parseInput = sys.argv[1]


def match(parseInput, val, i):
	if len(parseInput)-1 < i:
		raise Exception("Too short")
	print "Checking if '%s' is '%s' => %r" % (parseInput[i], val, parseInput[i]==i)
	return parseInput[i] == i

def T(parseInput, i):
	if match(parseInput, 'g', i):
		if(match(parseInput, 'b', i+1)):
			True
		elif match(parseInput, 'c', i+1):
			True
		else:
			raise Exception("nope")

		if match(parseInput, 'd', i+2):
			True
		else:
			raise Exception("nope")
	else:
		raise Exception("nope")


T(parseInput, 0)