import random

#
#  Generating random strings from a context-free grammar.
#
def noun():
    return random.choice(['idea', 'bagel', 'milk', 'cow'])

def verb():
    return random.choice(['sleeps', 'eats', 'swims', 'sprints'])

def article():
    return random.choice(['the', 'a'])

def adjective():
    return random.choice(['colorless','green','smelly'])

def adverb():
    return random.choice(['furiously','soothingly','intentionally'])

def pre_noun_phrase():
    return random.choice([[noun],[adjective, pre_noun_phrase]])

def noun_phrase():
    return [article, pre_noun_phrase]

def verb_phrase():
    return random.choice([[verb],[verb, adverb]])

def sentence():
    return [noun_phrase, verb_phrase]

def process(cfg):
    if isinstance(cfg, str):
	return cfg
    else:
	# we know it's an instance of a list of functions
	result = ""
	
	for item in cfg:
	    result += process(item()) + " "
	    
	return result.strip()