PureScript by Example - 4.17 Listing All Files - Exercise 1-3 Solutions

FileOperations.purs

module FileOperations where

-- 4.17 Listing All Files of PureScript by Example
-- N.B. This module relies extensively on a non-standard module Data.Path
--      whose source code can be found on
--      https://github.com/paf31/purescript-book/blob/master/exercises/chapter4/src/Data/Path.purs

import Prelude
import Data.Array
import Partial.Unsafe
import Data.Maybe
import Data.Path

-- Boilerplate code provided in 4.17 Listing All Files of PureScript by Example

allFiles :: Path -> Array Path
allFiles file = file : concatMap allFiles (ls file)

allFiles' :: Path -> Array Path
allFiles' file = file : do
  child <- ls file
  allFiles' child

-- Exercise 1
onlyFiles :: Path -> Array Path
onlyFiles path = if isDirectory path
  then concatMap onlyFiles (ls path)
  else pure path

-- Exercise 2
largestFile :: Path -> Path
largestFile path =
  foldl (\file1 file2 -> if unsafePartial fromJust (size file1) > unsafePartial fromJust (size file2)
    then file1
    else file2) (unsafePartial fromJust (head files)) files
  where
    files :: Array Path
    files = onlyFiles path

smallestFile :: Path -> Path
smallestFile path =
  foldl (\file1 file2 -> if unsafePartial fromJust (size file1) < unsafePartial fromJust (size file2)
    then file1
    else file2) (unsafePartial fromJust (head files)) files
  where
    files :: Array Path
    files = onlyFiles path

-- Exercise 3
whereIs :: String -> Maybe Path
whereIs = whereIs' root
  where
    whereIs' :: Path -> String -> Maybe Path
    whereIs' path name = if isDirectory path
      then (if null otherResults then result' else head otherResults)
      else Nothing
        where
          result' :: Maybe Path
          result' = if elem name (map filename (onlyFiles path))
            then Just path
            else Nothing
          otherResults :: Array Path
          otherResults =
            catMaybes (map (\path -> whereIs' path name) (ls path))