Nested Maybes

Main.purs

module Main where

import Prelude (Unit, pure, bind, ($), show, class Show)
import Effect (Effect)
import Data.Maybe (Maybe(Just, Nothing))
import Data.Array (head)
import TryPureScript (p, text, render)
import Data.Foldable (fold)


-- Data.Array provides `head` function which has to return a Maybe because the array could be empty

main :: Effect Unit
main = render $ fold
  [ p $ text $ showMaybe $ unpackNested nested
  , p $ text $ showMaybe $ unpackNested nested'
  ]
  
showMaybe :: forall a. (Show a) => Maybe a -> String
showMaybe (Just a) = show a
showMaybe Nothing = "Nothing"

nested :: Array (Array (Array Int))
nested = [[[1,2,3]]] 

nested' :: Array (Array (Array Int))
nested' = [[[]]]

unpackNested :: forall a. Array (Array (Array a)) -> Maybe a
unpackNested nest = do
  first  <- head nest
  second <- head first
  third  <- head second
  pure third