Monitoring

One process Pid1 can monitor another process Pid2. If Pid2 terminates, Pid1 will receive a ‘DOWN’ message from Pid2.

import Prelude
import Control.Process (killProc)
go :: forall a. IO a
go = do
  pid <- spawn proc
  ref <- monitor pid
  killProc pid
  receive msg -> return msg
proc :: Process ()
proc = receive _ -> return ()