Main.purs

module Main where

import Prelude

import Data.Foldable (sum)
import Data.List.Lazy (filter, takeWhile)
import Data.List.Lazy.Types (List)
import Data.Maybe (Maybe(..))
import Data.Tuple (Tuple(..))
import Data.Unfoldable (unfoldr)
import Control.Monad.Eff.Console (logShow)
import TryPureScript (render, withConsole)

fibs :: List Int
fibs =
  unfoldr next (Tuple 1 2)
  where
    next (Tuple i j) = Just (Tuple i (Tuple j (i + j)))

result :: Int
result =
  fibs
  # filter (\n -> n `mod` 2 == 0)
  # takeWhile (_ <= 4000000)
  # sum

main :: _
main = render =<< withConsole do
  logShow result