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