Is there some directory walker in Haskell?

Question

Is there some recursive directory walker in Haskell so I could write something like

listing <- walkDir "/tmp"

I would not like to write my own. I can install some dependency from cabal but I want it to be cross platform (at least Linux and Windows).

I wrote the [dir-tree](http://hackage.haskell.org/package/directory-tree) package which should allow a lazy `walkDir` to be defined pretty easily I would guess, e.g. with `toList` provided by the `Foldable` instance. — jberryman, Nov 10 '12 at 03:35

score 13 · Answer 1 · answered Nov 15 '12 at 11:47

13

Here is one way to list all Haskell files in a directory tree, using directory-tree that is not in a hidden directory (whose name starts with '.'):

import Data.Traversable (traverse)
import System.Directory.Tree (
    AnchoredDirTree(..), DirTree(..),
    filterDir, readDirectoryWith
    )
import System.FilePath (takeExtension)

listFilesDirFiltered = do
    _:/tree <- readDirectoryWith return "C:\\devmy\\code"
    traverse print $ filterDir myPred tree
    return ()
  where myPred (Dir ('.':_) _) = False
        myPred (File n _) = takeExtension n == ".hs"
        myPred _ = True

main = listFilesDirFiltered

Works on both Windows and Linux.

answered Nov 15 '12 at 11:47

Björn Lindqvist

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It's just a constructor defined in the library: http://hackage.haskell.org/packages/archive/directory-tree/0.11.0/doc/html/System-Directory-Tree.html – Mateusz Kowalczyk Aug 12 '13 at 20:11
1

I like this library a little better than the accepted answer - it's simpler and has less dependencies, yet still just as powerful. It's also compatible with lens, yet doesn't depended on the (huge) lens library if you're not using it. Here's a link to the main hackage page: [directory-tree](http://hackage.haskell.org/package/directory-tree) [EDIT: but don't get me wrong; FilePather is also excellent] – Yitz Aug 19 '13 at 17:42

score 6 · Answer 2 · edited Nov 03 '15 at 21:20

I have a recursive definition for traversing a directory using filepath package:

import Control.Monad
import System.Directory
import System.FilePath
import System.Posix.Files

-- | Traverse from 'top' directory and return all the files by
-- filtering out the 'exclude' predicate.
traverseDir :: FilePath -> (FilePath -> Bool) -> IO [FilePath]
traverseDir top exclude = do
  ds <- getDirectoryContents top
  paths <- forM (filter (not.exclude) ds) $ \d -> do
    let path = top </> d
    s <- getFileStatus path
    if isDirectory s
      then traverseDir path exclude
      else return [path]
  return (concat paths)

Thank you @StephaneRolland. – aycanirican Nov 04 '15 at 07:40 — aycanirican, Nov 04 '15 at 07:40

score 5 · Answer 3 · answered Nov 08 '12 at 21:16

5

http://hackage.haskell.org/package/FilePather has that sort of recursive directory walking functionality.

answered Nov 08 '12 at 21:16

singpolyma

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Is there some tutorial for that library? It does not look like easy one. – Trismegistos Nov 09 '12 at 09:29
I made use of it in https://github.com/singpolyma/imapmd, but only used the docs as presented on hackage. – singpolyma Nov 09 '12 at 18:19

danza · Answer 4 · 2017-01-19T13:46:47.853

2

The filemanip package provides powerful and elegant functions for that. For example it provides a fold function that will recursively call your function down a directory tree. As an example i used it here to recursively list files in a directory starting from the oldest

edited Jan 19 '17 at 13:46

answered May 22 '14 at 22:10

danza

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@Trismegistos There are some examples [in the source code](http://hackage.haskell.org/package/filemanip-0.3.6.2/docs/src/System-FilePath-Find.html) but it's certainly true that Haskell libraries tend to be under-documented in terms of practical, tutorial advice. I often find I get more out of messing around in ghci than reading the docs. – Daniel Lyons Nov 03 '15 at 21:27

Is there some directory walker in Haskell?

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