thrice

tail_cps.hs

tail_cps s k = k (tail s)

thrice_ausgabe.txt

*Main> thrice tail "foobar"
"bar"

thrice_cont.hs

tail_cont :: [a] -> Cont r [a]
tail_cont x = return $ tail x

thrice_cont :: (a -> Cont r a) -> a -> Cont r a
thrice_cont f x = do
  fx <- f x
  ffx <- f fx
  fffx <- f ffx
  return fffx

thrice_cont_ausgabe.txt

*Main> runCont (thrice_cont tail_cont "foobar") print
"bar"

thrice_cont_prime.hs

thrice_cont' :: (a -> Cont r a) -> a -> Cont r a
thrice_cont' f x = f x >>= f >>= f >>= return

thrice_cps.hs

thrice_cps :: (o -> (o -> r) -> r) -> o -> (o -> r) -> r
thrice_cps f_cps x k =
 f_cps x $ \fx ->
 f_cps fx $ \ffx ->
 f_cps ffx $ \fffx ->
 k fffx

thrice_cps_ausgabe.txt

Main*> thrice_cps tail_cps "foobar" print
"bar"

thrice_normal.hs

thrice :: (o -> o) -> o -> o
thrice f x = f (f (f x))