prop_evenNumberPlusOneIsOdd :: Integer -> Property prop_evenNumberPlusOneIsOdd x = even x ==> odd (x + 1)
If you want to check that a property holds given that a precondition holds, you can use the
==> operator. Note that if it's very unlikely for arbitrary inputs to match the precondition, QuickCheck can give up early.
prop_overlySpecific x y = x == 0 ==> x * y == 0 ghci> quickCheck prop_overlySpecific *** Gave up! Passed only 31 tests.