Haskell script that checks the number of files in a specified directory.

check-files.hs

#!/usr/bin/env stack
{- stack script
   --resolver lts-9.1
   --package turtle
   --package foldl
   --package system-filepath
   --package bytestring
   --package text
   --package containers
-}
{-# LANGUAGE OverloadedStrings #-}
import Turtle
import Data.List
import Prelude hiding (FilePath)
import qualified Control.Foldl as Fold
import qualified Filesystem.Path.CurrentOS as FS
import qualified Data.ByteString.Lazy as BS
import qualified Data.Set as Set
import Control.Applicative
import qualified Data.ByteString.Char8 as C8

-- this is faster than the Text-based version
dropPackageVersion :: FilePath -> C8.ByteString
dropPackageVersion = fst . C8.breakEnd (== '-') . FS.encode

parseDirectory :: Parser FilePath
parseDirectory = argPath "DIR" "The packages directory"

countFiles :: MonadIO io => FilePath -> io Int
countFiles dir = fold (ls dir) Fold.length

nubWith :: Ord b => (a -> b) -> [a] -> Set.Set b
nubWith = func Set.empty
  where
    func s _ [] = s
    func set f (x:xs)
      | Set.member x' set = func set f xs
      | otherwise = func (Set.insert x' set) f xs
      where x' = f x

listOfFiles :: MonadIO io => FilePath -> io [FilePath]
listOfFiles dir = fold (ls dir) Fold.list

numberOfDifferentPackages :: MonadIO io => FilePath -> io Int
numberOfDifferentPackages directory = do
  listOfPackages <- listOfFiles directory
  return $ (length . nubWith dropPackageVersion) listOfPackages

main :: IO ()
main = do
  directory <- options "" parseDirectory
  total <- countFiles directory
  diffs <- numberOfDifferentPackages directory

  printf ("# packages in this directory: " %w% "\n") total
  printf ("# different packages in this directory: " %w% "\n") diffs
                   

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