from itertools import imap, chain, count, islice, groupby, tee
from operator import add, mul
from heapq import merge
class clone(object):
'''A decorator to simplify the creation of recursively defined generators.'''
def __init__(self, generator):
self.clones = iter(tee(generator()))
self.cache = None
def __call__(self):
try:
self.cache = next(self.clones)
return next(self.clones)
except StopIteration:
self.clones = iter(tee(self.cache))
return next(self.clones)
# examples #
# helper function
def itail(iterable):
return islice(iterable, 1, None)
# Haskell -- fibonacci
# fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
@clone
def fibs():
for i in chain([0, 1], imap(add, fibs(), itail(fibs()))):
yield i
# Haskell -- factorial
# facs = 1 : zipWith (*) [1 ..] facs
@clone
def facs():
for i in chain([1], imap(mul, count(1), facs())):
yield i
# Haskell -- http://rosettacode.org/wiki/Hamming_numbers
#
# hamming = 1 : map (2*) hamming `union` map (3*) hamming `union` map (5*) hamming
#
# union a@(x:xs) b@(y:ys) = case compare x y of
# LT -> x : union xs b
# EQ -> x : union xs ys
# GT -> y : union a ys
# hamming numbers generator adapted from Raymond Hettinger's algorithm
# http://code.activestate.com/recipes/576961-technique-for-cyclical-iteration/
@clone
def hamming():
for i in (k for k, v in groupby(chain([1],
merge((2*x for x in hamming()),
(3*x for x in hamming()),
(5*x for x in hamming()))))):
yield i
Diff to Previous Revision
--- revision 1 2012-05-04 13:01:45
+++ revision 2 2012-05-04 14:09:14
@@ -3,7 +3,7 @@
from heapq import merge
class clone(object):
- '''A decorator to enable recursively defined, Haskell-style infinite lists.'''
+ '''A decorator to simplify the creation of recursively defined generators.'''
def __init__(self, generator):
self.clones = iter(tee(generator()))
self.cache = None
@@ -14,6 +14,8 @@
except StopIteration:
self.clones = iter(tee(self.cache))
return next(self.clones)
+
+# examples #
# helper function
def itail(iterable):
