Hello! It sounds like you're looking for the ParallelListComp language extension[1] Another option might be to leverage the Arbitrary typeclass in QuickCheck[2]. It has instances for tuples, so if each component of the tuple has an Arbitrary instance, you can generate the whole tuple with one invocation of "arbitrary". The CoArbitrary typeclass is also rather handy and clever, as it allows you to create random functions, as long as the arguments are instances of CoArbitrary and the result is an instance of Arbitrary. Your concept of specifying run length is very similar to QuickCheck's "size parameter". I hope that's helpful! -Michael [1] https://downloads.haskell.org/~ghc/7.8.3/docs/html/users_guide/syntax-extns.... [2] http://hackage.haskell.org/package/QuickCheck