Question

Been trying to write my own Prelude, and to write QuickCheck properties along with it. Writing Prelude is going well, but in doing the QuickCheck I have managed to get blocked early. Here are snippets of the 2 files I have:

— MyLude.hs

module MyLude where

import Prelude (Bool(..))

(&&) :: Bool -> Bool -> Bool
(&&) True a = a
(&&) _ _ = False

— MyLudeTest.hs

module MyLudeTest where

import qualified MyLude as P

prop_test_and a b = a && b == a P.&& b

Then in ghci I run:

:load MyLudeTest.hs
:m +Test.QuickCheck
quickCheck prop_test_and

and get the following error:

*** Failed! Falsifiable (after 1 test):
False
False

What confuses me is that I have implemented (||) and implemented a quickcheck property for it that does pretty much the same thing the prop_test_and does, and that seems to have no problems. What am I missing?

Answer 1

This is just operator precedence at work. Your property is parsed as:

prop_test_and a b = a && (b == a) P.&& b