Having fun with 'Learn PureScript" - naive 'whereIs' function implementation

file-operations.purs

module Data.FileOperations where

  import Prelude
  import Data.Maybe (Maybe(Nothing), Maybe(Just))
  import Data.String (contains, Pattern(Pattern))
  import Data.Array (foldl)
  import Data.Path

  whereIs :: Path -> String -> Maybe Path
  whereIs path filePattern =
      foldl (whereIsReducerFactory filePattern) Nothing $ transform (ls path)
        where
          transform :: Array Path -> Array (Maybe Path)
          transform arr =
            map (\item -> Just item) arr

          whereIsReducerFactory :: String -> Maybe Path -> Maybe Path -> Maybe Path
          whereIsReducerFactory file acc curr =
            case acc, curr of
              Just accValue, _ -> searchForFile accValue file
              _, Just currValue -> searchForFile currValue file
              _, _ -> Nothing

          searchForFile :: Path -> String -> Maybe Path
          searchForFile p f =
            case isDirectory p of
              true -> whereIs p f
              _ -> checkFile p f

          checkFile :: Path -> String -> Maybe Path
          checkFile p f =
            case contains (Pattern f) (filename p) of
                  true -> Just p
                  _ -> Nothing