rapid_check_forall.hs

forAll :: (Show a, Testable testable) => Gen a -> (a -> testable) -> Property
forAll argGen prop =
  Property $ Gen $ \rand ->             -- Create a new property that will
    let (rand1, rand2) = split rand     -- Split the generator in two
        arg = runGen argGen rand1       -- Use the first generator to produce an arg
        subProp = property (prop arg)   -- Use the `a` to access the sub-property
        result = runProp subProp rand2  -- Use the second generator to run it
    in overFailure result $ \failure -> -- Enrich the counter-example with `arg`
        failure { counterExample = show arg : counterExample failure }