úÎ Ò H SafeAbstract Stack data typeCreate new StackPush item onto Stack 0("x)("s)(stackPop (stackPush s x) == Just (s,x))<Pop most recently added item without removing from the Stack vstackPeek stackNew == Nothing ("x)("s)(stackPeek (stackPush s x) == Just x) ("s)(stackPeek s == fmap snd (stackPop s))'Pop most recently added item from Stack MstackPop stackNew == Nothing ("x)("s)(stackPop (stackPush s x) == Just (s,x))Test if stack is empty €stackIsEmpty stackNew == True ("x)("s)(stackIsEmpty (stackPush s x) == True) ("s)((stackSize s == 0) !Ô (stackIsEmpty s == True))1Compute number of elements contained in the Stack YstackSize stackNew == 0 ("x)("s)((stackSize s == n) !Ò (stackSize (stackPush s x) == n+1))      "Stack-0.2.0-C9ugMJ2Zd8ALB3qzyQ5riM Data.StackStackstackNew stackPush stackPeekstackPop stackIsEmpty stackSize $fReadStack $fShowStack