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module revtwice
/*
Reversing a list a number of times using Twice.
Increase stack size to 1m and heap size to 2m to run this program.
A list containing 25 integers is reversed 65536 times by means
of four applications of the higher order function Twice.
*/
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 [1..25]
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