TraceOff.hs

-- Communicating Haskell Processes.
-- Copyright (c) 2008, University of Kent.
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-- This module contains a trace-type that does not record anything.  This is
-- generally not needed (just use runCSP without tracing) but is included in
-- the library for completeness.
module Control.Concurrent.CHP.Traces.TraceOff (TraceOff, runCHP_TraceOff) where

import Control.Monad
import Data.Unique
import Text.PrettyPrint.HughesPJ

import Control.Concurrent.CHP.Base
import Control.Concurrent.CHP.ProcessId
import Control.Concurrent.CHP.Traces.Base



-- | A trace type that does not record anything.
newtype TraceOff a = TraceOff ()

instance Show (TraceOff a) where
  show = const ""

instance Trace TraceOff where
  runCHPAndTrace = liftM (flip (,) (TraceOff ())) . runCHPProgramWith (NoTrace rootProcessId)
  emptyTrace = TraceOff ()
  prettyPrint = const empty
  labelAll = const emptyTrace


-- | A type-constrained version of 'runCHPAndTrace'.  This is semantically identical
-- to 'runCHP', but this function is useful with the 'qcCHP'' function in the testing
-- module.
runCHP_TraceOff :: CHP a -> IO (Maybe a, TraceOff Unique)
runCHP_TraceOff = runCHPAndTrace