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 wrote:

2008/6/17 Hugo Pacheco :

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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

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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 dougal@dougalstanton.net // http://www.dougalstanton.net

-- www.di.uminho.pt/~hpacheco