Introduction

This provides file watching as a Streamly stream. You can either watch recursively (namely, a directory's contents and all its subdirectories as well), or not. You can also filter out file system events you are not interested in. Lastly, we provide a compositional scheme for constructing filters for file system events.

Example

This example program watches /home/koz/c-project (and any of its subdirectories) for added or modified files with a .c extension, and emits the change to the terminal, along with a timestamp of when it happened, forever:

{-# LANGUAGE LambdaCase #-}

import Streamly.FSNotify (EventPredicate, 
                          hasExtension, isDirectory, 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 ()