ContIf.hs

{-# LANGUAGE Rank2Types #-}
module Main where
-- data Cont r a = Cont { runCont :: (a -> r) -> r }

import Control.Monad.Cont

calculateLength :: [a] -> Cont r Int
calculateLength l = return (length l)

type ContS r a = (a -> r) -> r

type ContH a = forall r . (a -> r) -> r

-- iff :: Bool -> Cont () a -> Cont () a -> Cont a
iff :: Bool -> ContH a -> ContH a -> ContH a
iff b k1 k2 k = if b
        then k1 k
        else k2 k

returnH :: a -> ContH a
returnH = flip ($)

succK, predK :: Int -> ContS a Int

succH :: Int -> ContH Int
succH x k = k (succ x)

succK x k = k (succ x)
predK x k = k (pred x)

succM, predM :: Int -> Cont a Int

succM x = return (succ x)
predM x = return (pred x)

true, false :: a -> a -> a
true  x y = x
false x y = y

type BoolC = forall a . a -> a -> a

ifc :: BoolC -> a -> a -> a
ifc f x y = f x y

ifcK :: BoolC -> ContH a -> ContH a -> ContH a
ifcK b k1 k2 = \k -> ifc b (k1 k) (k2 k)