ghc's Int is 32-bit on 32-bit platforms, according to maxBound. On Mon, 21 Jan 2013 02:26:34 +0100 Benoit T <benoit.triquet@gmail.com> wrote:
On Mon, Jan 21, 2013 at 01:17:17AM +0200, miphis@meta.ua wrote:
The program looks like this:
--*********************** factorial :: Int->Int factorial n = product [1..n]
main = do print $ factorial 50 --***********************
And that yields "0" (no errors). Is it a bug or feature? :)
Int is fixed-size (*) and is expected to use modular arithmetics (**) therefore there is no notion of overflow, it just computes modulo maxBound::Int
You must have been using a 32-bit haskell, that uses full-word Int, such as HUGS, and it turns out that using 32-bit signed integers, you eventually get -2**31 (this happens for n==32) and then multiplying by any even integer yields 0 (34!==0).
GHC uses 31-bit or 63-bit Int (on 32- or 64-bit arch) and does not encounter this case before factorial 50 (however the answer is also not what you may have been expecting because it still doesn't fit).
cheers
*: this is specified in the standard **: this does not seem to be specified in the standard