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implementation module StdStack
import StdEnv
:: Stack a = Stack [a]
newStack :: Stack a
newStack = Stack []
push :: a (Stack a) -> Stack a
push x (Stack xs) = Stack [x:xs]
pushes :: [a] (Stack a) -> Stack a
pushes [] (Stack s) = Stack s
pushes [x:xs] (Stack s) = pushes xs (push x (Stack s))
pop :: (Stack a) -> Stack a
pop (Stack []) = abort "Can't pop from empty stack..."
pop (Stack [x:xs]) = Stack xs
popn :: Int (Stack a) -> Stack a
popn 0 s = s
popn n s = popn (n-1) (pop s)
top :: (Stack a) -> a
top (Stack []) = abort "Can't give top of empty stack..."
top (Stack [x:_]) = x
topn :: Int (Stack a) -> [a]
topn 0 _ = []
topn n x = [top x:topn (n-1) (pop x)]
elements :: (Stack a) -> [a]
elements (Stack s) = s
count :: (Stack a) -> Int
count (Stack []) = 0
count (Stack [_:xs]) = 1 + count (Stack xs)
Start = ( "s0 = newStack = ", s0,'\n'
, "s1 = push 1 s0 = ", s1,'\n'
, "s2 = pushes [2..5] s1 = ",s2,'\n'
, "s3 = pop s2 = ", s3,'\n'
, "s4 = popn 3 s3 = ", s4,'\n'
, "s5 = top s4 = ", s5,'\n'
, "s6 = topn 3 s2 = ", s6,'\n'
, "s7 = elements s2 = ", s7,'\n'
)
where
s0 = newStack
s1 = push 1 s0
s2 = pushes [2..5] s1
s3 = pop s2
s4 = popn 3 s3
s5 = top s4
s6 = topn 3 s2
s7 = elements s2
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