######################################################################
## From Diving into Python
##
## remember making plurals of words?
##

import re
import string                                                                     
def buildRule((pattern, search, replace)):                                        
    return lambda word: re.search(pattern, word) and re.sub(search, replace, word) 

def plural(noun, language='en'):                             
    lines = file('rules.%s' % language).readlines()          
    patterns = map(string.split, lines)                      
    rules = map(buildRule, patterns)                         
    for rule in rules:                                      
        result = rule(noun)                                  
        if result: return result                            


import re

def rules(language):
   for line in file('rules.%s' % language):
      pattern, search, replace = line.split()
      yield lambda word: re.search(pattern, word) and re.sub(search, replace, word)
      
def plural(noun, language='en'):      
   for applyRule in rules(language): 
      result = applyRule(noun)      
      if result: return result

######################################################################
## Fibonacci

def fib():
    x = 0
    y = 1
    while True:
        x, y = y, x+y
        yield x

######################################################################
## Streams

def ones():
   x = 1
   while True:
      yield x

def twos():
   o1 = ones()
   o2 = ones()
   while True:
      yield o1.next() + o2.next()
      
def ints():
   o = ones()
   i = ints()
   yield 1
   while True:
      yield i.next() + o.next()

def odd():
   i = ints()
   while True:
      a = i.next()
      if a % 2:
         yield a


######################################################################
## Sieve of Eratosthenes
      

def exclude_multiples(n, ints):
	for i in ints:
		if (i % n):
			yield i

def sieve(ints):
    while 1:
        prime = ints.next()
        if prime == 1:
            prime = ints.next()
        yield prime
        ints = exclude_multiples(prime, ints)