Example

Here is a program which watches /home/georgefst/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.

import Data.Functor.Contravariant (Predicate (Predicate))
import Streamly.Data.Fold qualified as SF
import Streamly.Data.Stream.Prelude qualified as SP
import System.FilePath (isExtensionOf, (</>))

import Streamly.FSNotify

isCSourceFile :: Predicate Event
isCSourceFile = Predicate \e ->
    "c" `isExtensionOf` eventPath e && eventIsDirectory e == IsFile

notDeletion :: Predicate Event
notDeletion = Predicate \case
    Removed{} -> False
    _ -> True

srcPath :: FilePath
srcPath = "/" </> "home" </> "gthomas" </> "c-project"

main :: IO ()
main = SP.fold (SF.drainMapM go) $ watchTree srcPath $ isCSourceFile <> notDeletion
  where
    go = \case
        Added p t _ -> putStrLn $ "Created: " ++ show p ++ " at " ++ show t
        Modified p t _ -> putStrLn $ "Modified: " ++ show p ++ " at " ++ show t
        _ -> pure ()