Page 562 exercises

Spec.hs

module Page562Tests where

import Page562
import Test.QuickCheck
import Data.List (sort)

--Ex 1
halfIdentity :: (Fractional a, Num a) => a -> a
halfIdentity = (*2) . half

prop_halfIdentity :: Float -> Bool
prop_halfIdentity x = x == halfIdentity x

--Ex 2
listGen :: Arbitrary => Gen [a]
listGen = do
  a <- arbitrary
  return (a)

listIsOrdered :: [a] -> Bool
listIsOrdered xs =
  snd $ foldr go (Nothing, True) xs
  where go _ status@(_, False) = status
        go y (Nothing, t) = (Just y, t)
        go y (Just x, t) = (Just y, x >= y)

prop_listOrdered :: Property
prop_listOrdered =
  forAll listGen (\l -> (listIsOrdered $ sort l))

runQC :: IO ()
runQC = do
  quickCheck prop_halfIdentity
  quickCheck prop_listOrdered