Quickcheck in Elm

Quickcheck.elm

quickCheck : Generator a -> Int -> (a -> Bool) -> String
quickCheck randomGenerator numberOfCases testingCondition =
  let listGenerator = list numberOfCases <| randomGenerator
      testInputs = fst <| generate listGenerator (initialSeed 1)
      getOutput input = (input, testingCondition input)
      testOutputs = map getOutput testInputs
      failingOutputs = filter (\x -> (snd x) == False) testOutputs
      successString = "Ok, passed " ++ (toString numberOfCases) ++ " tests."
      failingString fail = "The following input has failed the test: " ++ (toString fail)
  in
    if failingOutputs == []
    then successString
    else failingString <| fst <| head failingOutputs
    
{-
Examples : 

> quickCheck (float 0 1) 100 (\x -> (x + 1) == x)
"The following input has failed the test: 0.35925459858478387"

> quickCheck (float 0 1) 1000 (\x -> x == x)
"Ok, passed 1000 tests."
-}