IO.hs

-- |
-- Module:     FRP.NetWire.IO
-- Copyright:  (c) 2011 Ertugrul Soeylemez
-- License:    BSD3
-- Maintainer: Ertugrul Soeylemez <es@ertes.de>
--
-- Access the rest of the universe.

module FRP.NetWire.IO
    ( -- * IO Actions
      execute,
      executeOnce
    )
    where

import Control.Exception.Control
import Control.Monad
import Control.Monad.IO.Control
import FRP.NetWire.Tools
import FRP.NetWire.Wire


-- | Execute the IO action in the input signal at every instant.
--
-- Note: If the action throws an exception, then this wire inhibits the
-- signal.
--
-- Inhibits on exception.  No feedback.

execute :: MonadControlIO m => Wire m (m a) a
execute = mkGen $ \_ c -> liftM (, execute) (try c)


-- | Executes the IO action in the input signal and inhibits, until it
-- succeeds without an exception.  Keeps the result forever.
--
-- Inhibits until the first result value.  No feedback.

executeOnce :: MonadControlIO m => Wire m (m a) a
executeOnce =
    mkGen $ \_ c -> do
        mx <- try c
        return (mx, either (const executeOnce) constant mx)