Main.purs

module Main where

import Prelude
import Control.Monad.Eff.Console (log, logShow)
import TryPureScript (render, withConsole)
import Control.Lazy (fix)


-- From https://github.com/awkure/purescript-birds/blob/v1.0.4/src/Aviary/Birds.purs#L38-L38
fixB :: forall a. (a -> a) -> a
fixB f = (compose f fixB) f
--fixB f = (f <<< fixB) f

-- From https://en.wikipedia.org/wiki/Fixed-point_combinator#Strict_functional_implementation
fixW :: forall a b. ((a -> b) -> a -> b) -> a -> b
fixW f x = f (fixW f) x


factF :: (Int -> Int) -> Int -> Int
factF fact' i = case i of
  0 -> 1
  i' -> i' * fact' (i' - 1)

-- !!! The Birds implementation doesn't work.
fact = fixW factF


main = render =<< withConsole do
  logShow $ fact 4