I'm writing tests using QuickCheck to test data types that are not an instance of QC's Arbitrary. To prevent orphan instances I use forAll function instead of instantiating these types as Arbitrary. The problems arise when I need to generate several different variables for one test. To do this I either nest calls to forAll or create a pair generator like this: genPair = liftM2 (,) (myGenerator1) (myGenerator2) Running time of such tests is very long (both with nesting forAll and using pair generator) and it gets shorter when I resize myGenerator1 and myGenerator2. This leads me to conslusion that, due to nesting of generators QC is generating 100*100*100 test cases instead of 100. How do I "flatten" my generators to always get 100 test cases (or whatever the default number of test is)? Janek