You are right! If I try to compile it, then it complains about a Show instance for a, what in fact forces a monomorphic type signature for t.
I have found under Test.Quickcheck.Poly a way to generate Int values for a polymorphic type, but because it requires an abstraction Poly a for some type a I do not see how it can improve. What it concretely states the module is - This is the basic pseudo-polymorphic object. - The idea is you can't cheat, and use the integer - directly, but need to use the abstraction. Is it possible to cheat? I would like to... Thanks, hugo On Tue, Jun 17, 2008 at 12:17 PM, Sebastiaan Visser <[EMAIL PROTECTED]> wrote: > On Jun 17, 2008, at 11:53 AM, Hugo Pacheco wrote: > >> Hi all, >> >> There is something about polymorphic tests in QuickCheck that I do not >> understand. >> >> If you write the simplest dummy test function >> >> tst :: a -> Bool >> tst _ = True >> >> and evaluate it we get >> >> > verboseCheck tst >> 0: >> () >> 1: >> () >> ... >> > > > How come did the polymorphic value a get instanciated to ()? Is this done >> via the Testable type class? >> Could someone please explain this to me? I'm not saying it does not make >> sense, but I would like to understand how it works. Being possible to change >> this behavior, this is, assign another "default type" whenever polymorphic >> types occur, would be awesome. >> > > I think it is GHCi that is instantiating the type with (). Try compiling > the program, it will probably be rejected by the compiler when you do not > specify a concrete type. > > You can, for example, try this: > > verboseCheck (tst :: [Int] -> Bool) > > Cheers, >> hugo >> > -- www.di.uminho.pt/~hpacheco
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
