Re: [Haskell-cafe] Polymorphic QuickCheck arguments
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
Re: [Haskell-cafe] Polymorphic QuickCheck arguments
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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic QuickCheck arguments
It does not seem like printing the result value from IO (), because with a more complicated example for lists. t :: [a] -> Bool t x = True then it randomly generates values of type [()]. *Quick> verboseCheck t 0: [] 1: [()] 2: [(),(),()] 3: [] 4: [()] 5: [(),(),(),()] I just wonder how the a got instantiated to (). Thanks, hugo On Tue, Jun 17, 2008 at 11:05 AM, Dougal Stanton <[EMAIL PROTECTED]> wrote: > 2008/6/17 Hugo Pacheco <[EMAIL PROTECTED]>: > > 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? > > I haven't got something here to check with, but from the formatting it > looks like every odd line is a randomly-chosen boolean value, and the > following line is the result? It might be just printing the result > value of IO (). Maybe try a more complete test to see how that looks? > > Cheers, > > D > > > -- > Dougal Stanton > [EMAIL PROTECTED] // http://www.dougalstanton.net > -- www.di.uminho.pt/~hpacheco ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic QuickCheck arguments
2008/6/17 Hugo Pacheco <[EMAIL PROTECTED]>: > 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? I haven't got something here to check with, but from the formatting it looks like every odd line is a randomly-chosen boolean value, and the following line is the result? It might be just printing the result value of IO (). Maybe try a more complete test to see how that looks? Cheers, D -- Dougal Stanton [EMAIL PROTECTED] // http://www.dougalstanton.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
