# ``streamly-fsnotify``
## What's the deal with this library?
[``streamly``][1] is an undoubtedly awesome library - [fast][2], 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.
```haskell
{-# LANGUAGE LambdaCase #-}
import Streamly.FSNotify (EventPredicate,
hasExtension, is Directory, invert, isDeletion, conj,
watchTree)
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!
## License
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 ``LICENSE.md`` file.
[1]: http://hackage.haskell.org/package/streamly
[2]: https://github.com/composewell/streaming-benchmarks