Stack.hs

-- | Abstract Stack data type
module Data.Stack (
    Stack,
    stackNew,
    stackIsEmpty,
    stackPush,
    stackPeek,
    stackPop,
    stackSize,
  )
  where

-- | Abstract Stack data type
data Stack a = Stack [a] deriving (Read,Show)

-- | Create new Stack
stackNew :: Stack a
stackNew = Stack []

-- | Test if stack is empty
stackIsEmpty :: Stack a -> Bool
stackIsEmpty (Stack []) = True
stackIsEmpty (Stack _)  = False

-- | Push item onto Stack
stackPush :: Stack a -> a -> Stack a
stackPush (Stack items) item = Stack (item : items)

-- | Pop most recently added item without removing from the Stack
stackPeek :: Stack a -> a
stackPeek (Stack items) = head items

-- | Pop most recently item from Stack
stackPop :: Stack a -> (Stack a, a)
stackPop (Stack items) = (Stack (tail items), stackPeek (Stack items))

-- | Compute number of elements contained in the Stack
stackSize :: Stack a -> Int
stackSize (Stack items) = length items