Re: [Haskell-cafe] Type classes and type equality

At Mon, 16 Apr 2007 13:44:13 +0100, Neil Mitchell wrote:

Hi,

So my question is if this is safe? Will the compiler always pick the "right one"? Is there a better way to do this?

I noticed that the results can be a bit suprising sometimes. See if you can predict the answers to these (in ghci):

same 1 1

let x = (undefined :: a) in same x x

f :: a -> Bool f a = same a a

f (undefined :: a)

Here is what ghci says: *Main> same 1 1 False *Main> :t 1 1 :: forall t. (Num t) => t *Main> let x = (undefined :: a) in same x x False

f :: a -> Bool f a = same a a

*Main> f (undefined :: a) True I'm not saying anything is wrong here. Just be careful how you use it :) j.