implementation module StdStack import StdEnv import StdList :: Stack a :== [a] newStack :: (Stack a) newStack = [] push :: a (Stack a) -> (Stack a) push a s = [a] ++ s pop :: (Stack a) -> (Stack a) pop [a:s] = s pop [] = [] popn :: Int (Stack a) -> (Stack a) popn 0 s = s popn n s = popn (n-1) (pop s) pushes :: [a] (Stack a) -> (Stack a) pushes [] s = s pushes a s = pushes (tl a) (push (hd a) s) top :: (Stack a) -> a top [] = abort "`top s` with s = []" top s = hd s topn :: Int (Stack a) -> [a] topn n s | n > length s = abort "`topn n s` with n > length s" | otherwise = take n s count :: (Stack a) -> Int count s = length s elements :: (Stack a) -> [a] elements s = s 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' // , "s8 = push 10 s1 = ", s8,'\n' // , "s9 = popn 10 s8 = ", s9,'\n' // , "sa = topn 5 s4 = ", sa,'\n' // , "sb = top s0 = ", sb,'\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 // s8 = push 10 s1 // s9 = popn 10 s8 // sa = topn 5 s4 // sb = top s0