Hi,

I am trying to use Quickcheck to check that pushing an element increases the size of a stack.

Something like:

prop_size2 x s = (size (Push x s)) > (size s)

Is this possible? Below is my effort using an empty stack.

Thanks in advance,

Pat

module Stack (empty, push, pop, top, isEmpty) where

import Test.QuickCheck

data Stack a = Empty | Push a (Stack a) deriving Show

empty :: Stack a

empty = Empty

push :: a -> Stack a -> Stack a

push x ss = Push x ss

pop :: Stack a -> Stack a

pop Empty = error "pop emptyStack"

pop (Push x ss) = ss

top :: Stack a -> a

top Empty = error "top emptyStack"

top (Push x ss) = x

isEmpty :: Stack a -> Bool

isEmpty Empty = True

isEmpty (Push x ss) = False

size :: (Stack a) -> Int

size Empty = 0

size (Push x ss) = succ (size ss)

prop_size x = (size (Push x Empty)) > (size Empty)

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