iavor.diatchki:
Hello, I think that it is a really bad idea to make 'unsafeCoerce' a part of the standard libraries. As far as I understand, 'unsafeCoerce' is only "safe" if the programmer assumes something about the representations of values (in particular, that values of different types have the same representations). Haskell makes no such guarantees so, by definition, any program that uses 'unsafeCoerce' is using an implementation specific extension. I was trying ot think of cases where 'unsafeCoerce' might be somewhat safe, and the main example I came up with is when the coersion happens on a phantom type. Are there other reasonably portable examples?
Perhaps the implementations of Data.Typeable (assuming the underlying Typeable stuff was portable): cast :: (Typeable a, Typeable b) => a -> Maybe b cast x = r where r = if typeOf x == typeOf (fromJust r) then Just $ unsafeCoerce x else Nothing Its another case of the programmer having a proof not expressible in the type system. I suspect there will be more of these in the future as people write more and more proof/type system preprocessing tools and compilers. -- Don