On 9/17/07, Lorenzo Stella <[EMAIL PROTECTED]> wrote: > Hi all, > I haven't experienced functional programming very much, but now I'm > trying to learn Haskell and I've learned that: 1) in functional > programming LISTS are fundmental; 2) any "cycle" in FP become > recursion. > I also know that Python got some useful tool such as map, filter, > reduce... so I told: "let's try some FP-style programming with > Python!". I took a little example of Haskell: > > listprimes :: Integer -> [Integer] > listprimes n = if n == 0 then sieve [2..] else sieve [2..(n-1)] > where > sieve [] = [] > sieve (p:xs) = p : sieve (filter (\x -> mod x p > 0) xs) > > and I tried to "translate" it in Python: > > def sieve(s): > if s == []: > return [] > else: > return [s[0]] + sieve(filter((lambda x: x % s[0] > 0), > s[1:])) > > def listprimes(n): > return sieve(range(2,n)) > > These should be almost the same: listprimes actually lists prime > integers up to n-1. The result is: Haskell implementation works well, > maybe it's not the better way to do it, but it does what I wanted. > Python implementation gives me > > RuntimeError: maximum recursion depth exceeded in cmp > > My question is: how can we call a language "functional" if it's major > implementation has a limited stack? Or is my code wrong?
Python does not optimize tail recursion. You can increase the maximum recursion limit with sys.setrecursionlimit, but the code will still be slow. I am a fan of functional programming languages (including Haskell!), but I wouldn't try to write functional code in Python -- the language isn't optimized for this type of code, and the syntax it provides isn't very elegant, compared to other functional languages. If you want to write functional code, use a real functional language! -- Evan Klitzke <[EMAIL PROTECTED]> -- http://mail.python.org/mailman/listinfo/python-list
