System.FSNotify

Minimal example:

{-# LANGUAGE OverloadedStrings #-} -- for FilePath literals

import System.FSNotify
import Control.Concurrent (threadDelay)
import Control.Monad (forever)

main =
  withManager $ \mgr -> do
    -- start a watching job (in the background)
    watchDir
      mgr          -- manager
      "."          -- directory to watch
      (const True) -- predicate
      print        -- action

    -- sleep forever (until interrupted)
    forever $ threadDelay maxBound

Events

data Event

A file event reported by a file watcher. Each event contains the canonical path for the file and a timestamp guaranteed to be after the event occurred (timestamps represent current time when FSEvents receives it from the OS and/or platform-specific Haskell modules).

Constructors

Added FilePath UTCTime

Modified FilePath UTCTime

Removed FilePath UTCTime

Instances

Eq Event

Show Event

type EventChannel = Chan Event

eventTime :: Event -> UTCTime

Helper for extracting the time associated with an event.

eventPath :: Event -> FilePath

Helper for extracting the path associated with an event.

type Action = Event -> IO ()

An action to be performed in response to an event.

type ActionPredicate = Event -> Bool

A predicate used to determine whether to act on an event.

Starting/Stopping

data WatchManager

Watch manager. You need one in order to create watching jobs.

withManager :: (WatchManager -> IO a) -> IO a

Perform an IO action with a WatchManager in place. Tear down the WatchManager after the action is complete.

startManager :: IO WatchManager

Start a file watch manager. Directories can only be watched when they are managed by a started watch watch manager. When finished watching. you must release resources via stopManager. It is preferrable if possible to use withManager to handle this automatically.

stopManager :: WatchManager -> IO ()

Stop a file watch manager. Stopping a watch manager will immediately stop watching for files and free resources.

defaultConfig :: WatchConfig

Default configuration

data WatchConfig

Watch configuration

Constructors

WatchConfig

Fields

confDebounce :: Debounce

Debounce configuration

confPollInterval :: Int

Polling interval if polling is used (microseconds)

confUsePolling :: Bool

Force use of polling, even if a more effective method may be available. This is mostly for testing purposes.

data Debounce

This specifies whether events close to each other should be collapsed together, and how close is close enough.

Constructors

DebounceDefault

perform debouncing based on the default time interval

Debounce NominalDiffTime

perform debouncing based on the specified time interval

NoDebounce

do not perform debouncing

withManagerConf :: WatchConfig -> (WatchManager -> IO a) -> IO a

Like withManager, but configurable

startManagerConf :: WatchConfig -> IO WatchManager

Like startManager, but configurable

type StopListening = IO ()

An action that cancels a watching/listening job

isPollingManager :: WatchManager -> Bool

Does this manager use polling?

Watching

watchDir :: WatchManager -> FilePath -> ActionPredicate -> Action -> IO StopListening

Watch the immediate contents of a directory by committing an Action for each event. Watching the immediate contents of a directory will only report events associated with files within the specified directory, and not files within its subdirectories. No two events pertaining to the same FilePath will be executed concurrently.

watchDirChan :: WatchManager -> FilePath -> ActionPredicate -> EventChannel -> IO StopListening

Watch the immediate contents of a directory by streaming events to a Chan. Watching the immediate contents of a directory will only report events associated with files within the specified directory, and not files within its subdirectories.

watchTree :: WatchManager -> FilePath -> ActionPredicate -> Action -> IO StopListening

Watch all the contents of a directory by committing an Action for each event. Watching all the contents of a directory will report events associated with files within the specified directory and its subdirectories. No two events pertaining to the same FilePath will be executed concurrently.

watchTreeChan :: WatchManager -> FilePath -> ActionPredicate -> EventChannel -> IO StopListening

Watch all the contents of a directory by streaming events to a Chan. Watching all the contents of a directory will report events associated with files within the specified directory and its subdirectories.