Hi, the difference is that you restrict your function to Int, whereas the default type is Integer. See: http://www.haskell.org/onlinereport/decls.html#sect4.3.4 and http://www.haskell.org/onlinereport/basic.html#sect6.4 hth, claus btw, you can ask ghci to give you the type of each expression you evaluate: Prelude> :set +t Prelude> 2^128 340282366920938463463374607431768211456 cmTypeOfName: it it :: Integer Prelude> 2^128 :: Int 0 cmTypeOfName: it it :: Int Prelude> maxBound :: Int 2147483647 cmTypeOfName: it it :: Int Prelude> maxBound :: Integer <interactive>:1:0: No instance for (Bounded Integer) arising from use of `maxBound' at <interactive>:1:0-7 Probable fix: add an instance declaration for (Bounded Integer) In the expression: maxBound :: Integer In the definition of `it': it = maxBound :: Integer ----- Original Message ----- From: "ting wang" <tting.wang@gmail.com> To: <haskell@haskell.org> Sent: Saturday, April 16, 2005 12:03 AM Subject: [Haskell] big integer in haskell

Hello all, I am a new learner, and i am trying to write a function to calculate factorial of a natural number: (I use ghc 6.4, window xp) fac :: Int -> Int fac n | n == 0 = 1 | n > 0 = fac (n-1) * n | otherwise = 0 this works when n < 14 and result is 1278945280, when n > 14 the answer is not right n = 15 result is 2004310016. I know it is maybe because of overflow. So i calclate 2^32, 2^64, 2^128 the result correct and is much bigger as 14!,Why? 2^n use some big integer or my implementation of n! is not correct, I'm really confused.

Someone can help me?

Thanks Ting Wang _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell