streamly-fsnotify: Folder watching as a Streamly stream.

[ bsd3, library, streamly, system ] [ Propose Tags ]

Provides Streamly streams for both single-level and recursive folder watching. Also contains a principled and compositional system for filtering file system events.

[Skip to Readme]


[Index] [Quick Jump]


Maintainer's Corner

Package maintainers

For package maintainers and hackage trustees


Versions [RSS],,,,
Change log
Dependencies base (>=4.9 && <5), fsnotify (>= && <, paths (>= && <, semirings (>=0.5.2 && <0.6.0), streamly (>=0.7.0 && <0.8.0), text (>= && <, time (>=1.9.3 && <2.0.0) [details]
License GPL-3.0-or-later
Copyright (C) Koz Ross 2019
Author Koz Ross
Category Streamly
Home page
Uploaded by koz_ross at 2019-12-06T20:17:51Z
Distributions NixOS:
Reverse Dependencies 2 direct, 0 indirect [details]
Downloads 1189 total (13 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Docs uploaded by user
Build status unknown [no reports yet]

Readme for streamly-fsnotify-

[back to package description]


What's the deal with this library?

streamly is an undoubtedly awesome library - fast, flexible, and well-documented. File system watching is a natural fit for a streaming library, and this is exactly what streamly-notify provides you.

As an example, here is a program which watches /home/koz/c-project/ and any of its subdirectories for added or modified C source files (which we take to be anything with a .c extension). This program then writes that the event occurred, to what file, and when, forever.

{-# LANGUAGE LambdaCase #-}

import Streamly.FSNotify (EventPredicate,
                          hasExtension, is Directory, invert, isDeletion, conj,
import System.Path (FsPath, FileExt, fromFilePath)

import qualified Streamly.Prelude as SP

-- conj -> both must be true
-- invert -> true when the argument would be false and vice versa
isCSourceFile :: EventPredicate
isCSourceFile = hasExtension (FileExt "c") `conj` (invert isDirectory)

notDeletion :: EventPredicate
notDeletion = invert isDeletion

srcPath :: FsPath
srcPath = fromFilePath "/home/koz/c-project"

-- first value given by watchTree stops the watcher
-- we don't use it here, but if you want to, just call it
main :: IO ()
main = do (_, stream) <- watchTree srcPath (isCSourceFile `conj` notDeletion)
          SP.drain . SP.mapM go $ stream
  where go = \case (Added p t _) -> putStrLn ("Created: " ++ show p ++ " at " ++ show t)
                   (Modified p t _) -> putStrLn ("Modified: " ++ show p ++ " at " ++ show t)
                   _ -> pure ()

That seems pretty cool! What kind of features can I expect?

  • Cross-platform - should work anywhere both streamly and fsnotify do.
  • Efficient (event-driven, so won't shred your CPU or load your RAM).
  • Able to do one-level and recursive watching.
  • Extensive set of filtering predicates, so you don't have to see events you don't care about!
  • Compositional and principled treatment of file paths and event filtering predicates.

Sounds good? Can I use it?

We've test-built this library for GHCs 8.2.2 through 8.8.1 on GNU/Linux. In theory, streamly-fsnotify should work everywhere both streamly and fsnotify will, which includes older GHCs (7.10) and other OSes (such as Windows). However, we haven't tried it ourselves - let us know if you do!


This library is under the GNU General Public License, version 3 or later (SPDX code GPL-3.0-or-later). For more details, see the file.