Modifiers for test data.

These types do things such as restricting the kind of test data that can be generated. They can be pattern-matched on in properties as a stylistic alternative to using explicit quantification.

Examples:

 -- Functions cannot be shown (but see Test.QuickCheck.Function) prop_TakeDropWhile (Blind p) (xs :: [A]) = takeWhile p xs ++ dropWhile p xs == xs 

 prop_TakeDrop (NonNegative n) (xs :: [A]) = take n xs ++ drop n xs == xs 

 -- cycle does not work for empty lists prop_Cycle (NonNegative n) (NonEmpty (xs :: [A])) = take n (cycle xs) == take n (xs ++ cycle xs) 

 -- Instead of forAll orderedList prop_Sort (Ordered (xs :: [OrdA])) = sort xs == xs