-- QuickCheck experiments/play

module Main where

import Test.QuickCheck
import Control.Monad

newtype Int' = Int' {unInt' :: Int}
  deriving (Eq,Ord,Show)

prop_IsEven :: Int -> Bool
prop_IsEven = even

prop_IsEven' :: Int' -> Bool
prop_IsEven' = even . unInt'

q0  = quickCheck (\x ->             prop_IsEven x)
q0b = quickCheck (\x -> collect x $ prop_IsEven x)

q1  = quickCheck (\x -> not (odd x) ==>             prop_IsEven x)
q1b = quickCheck (\x -> not (odd x) ==> collect x $ prop_IsEven x)

q2  = quickCheck (\x -> not (odd $ unInt' x) ==>             prop_IsEven' x)
q2b = quickCheck (\x -> not (odd $ unInt' x) ==> collect x $ prop_IsEven' x)

genEven1 :: Gen Int
genEven1 = do i <- arbitrary 
              return (i*2)

genEven2 :: Gen Int
genEven2 = frequency  $ zip (iterate (2*) 1) $
           map return $ reverse l
  where l = [2,4..20]
        len = length l

q3  = quickCheck (forAll genEven2 (\x -> not (odd x) ==> collect x $ prop_IsEven x))

instance Arbitrary Int' where
  arbitrary = fmap Int' genEven2

{-
instance Arbitrary Int' where
  arbitrary = oneof $
              map (return . Int') [2,4..10]

instance Arbitrary Int' where
  arbitrary = liftM Int' arbitrary

instance Arbitrary Int' where
  arbitrary = do i <- arbitrary
                 return (Int' i)
-}

main = q2b