Bryan O'Sullivan wrote:
Milos Hasan wrote:
so let's say I want to generate a list of N random floats. The elegant way of doing it would be to create an infinite lazy list of floats and take the first N, but for N = 1,000,000 or more, this overflows the stack. The reason is apparently that the take function is not tail-recursive, and so it uses O(N) stack space..
You might want to post your code. The reason take isn't tail recursive is that it will be evaluated lazily, so it will not consume O(n) stack space.
Yup, see the code I sent to Luke Palmer. The problem is that I really need the whole list to do further processing on it, instead of just consuming the elements one-by-one as they are produced by the random generator. I'm trying to build a search tree, but for simplicity you might assume that I just need to sort the list (or any other operation that is not a simple fold).
However, using take is the wrong approach anyway, as the user of the random numbers needs to return the unconsumed portion of the list so that the next user can consume them. This is why code that uses random numbers is usually written in the context of a state monad, such as MonadRandom: http://www.haskell.org/haskellwiki/New_monads/MonadRandom
That sounds interesting, but I'm not sure it's the randomness that's the problem here. I could as well have a completely deterministic function f :: Int -> Float, and I could try to produce the list "map f [1..1000000]", hitting the same issue. Cheers, Milos