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magnusth
playing with callCC
255 days ago

half :: Int -> (Int -> Cont r Int) -> Cont r Int
half n next = if n `mod` 2 == 0
        then next (n `div` 2)
        else return (-1)

> runCont (callCC (half 4)) (2 *)
4
> runCont (callCC (half 3)) (2 *)
-2

magnusth
the expected results using callCC
255 days ago

half :: Int -> (Int -> Cont r Int) -> Cont r Int
half n next = if n `mod` 2 == 0
        then next (n `div` 2)
        else return (-1)

double :: Int -> Cont r Int
double = return . (2 *)

> runCont (callCC $ \ e -> half 3 e >>= double) id
-1
> runCont (callCC $ \ e -> half 4 e >>= double) id
4

magnusth
correcting definition of half
255 days ago

half :: Int -> (Int -> Cont r Int) -> Cont r Int
half n exit = if n `mod` 2 == 0
        then return (n `div` 2)
        else exit (-1)

double :: Int -> Cont r Int
double = return . (2 *)

> runCont (callCC $ \ e -> half 3 e >>= double) id
-1
> runCont (callCC $ \ e -> half 4 e >>= double) id
4