module revtwice

/*
Reversing a list a number of times using Twice.

Increase stack size to 1m and heap size to 4m to run this program.

A list containing 25 integers is reversed 65536 times by means
of four applications of the higher order function Twice.
*/

(<) infix 4 :: !Int !Int -> Bool
(<) a b = code inline {
	ltI
}

(+) infixl 6 :: !Int !Int -> Int
(+) a b = code inline {
	addI
}

(-) infixl 6 :: !Int !Int -> Int
(-) a b = code inline {
	subI
}

fromto :: !Int !Int -> [Int]
fromto a b
| b < a     = []
| otherwise = [a:fromto (a+1) b]

//import StdInt, StdEnum

Revv:: [Int] -> [Int]
Revv l  =  Rev l []
where
	Rev::[Int] [Int] -> [Int]
	Rev [x:r] list	=  Rev r [x : list]
	Rev []    list	=  list

Twice::(x -> x) x -> x
Twice f x =  f (f x)

Start::[Int]
Start = Twice Twice Twice Twice Revv (fromto 1 25)