composability-example06.purs

module Main where

import Prelude

import Control.Comonad (class Comonad, class Extend, extract)
import Control.Monad.Eff.Console (logShow)

-- Javascript - const Functor = x => ({})
newtype Box a = Box a
-- Javascript - map: f => (f(x))
instance functorBox :: Functor Box where
  map f (Box x) = Box (f x)
-- Javascript - fold: f => f(x)
instance extendBox :: Extend Box where
  extend f m = Box (f m)
instance comonadBox :: Comonad Box where
  extract (Box x) = x

app :: Int -> Int
app n =
  Box n #
  map (\n -> n * 2) #
  map (\n -> n + 1) #
  extract


main = do
  logShow $ app $ 10
  -- 21