[Haskell-cafe] [Haskell] Silent error

[Henning Thielemann]

On Mon, 21 Jan 2013, miphis at 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? :)

This question is certainly better posted to haskell-cafe.

The answer is: Int has limited bitsize (32 ord 64 bit depending on your 
machine), thus it computes factorial modulo 2^32 or 2^64. You can get the 
correct result by replacing Int by Integer.