On Wed, Oct 7, 2015 at 11:33 AM, Ozgur Akgun
This is not true, ==> still does generate and test.
I could have phrased that better. Sure, it generates values, but it will never provide them to your test, so your logic is simpler.
Prelude> import Test.QuickCheck Prelude Test.QuickCheck> let f x = x == 13 ==> mod x 2 == 1 Prelude Test.QuickCheck> quickCheck f *** Gave up! Passed only 6 tests.
That's unlikely to be a problem given the test inputs in the original question, but yes, it is certainly an issue to know about. Roelof - The issue Ozgur is demonstrating is that the ==> operator will just discard test inputs that were generated but which did not satisfy the predicate (here that x == 13). QuickCheck will eventually stop trying to generate inputs (you can tune this), and produce something like the above result. --Rogan
Also try verboseCheck to see what values are generated.
Ozgur