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
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