diff options
Diffstat (limited to 'compiler/utils')
| -rw-r--r-- | compiler/utils/IOEnv.hs | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/compiler/utils/IOEnv.hs b/compiler/utils/IOEnv.hs index 583e875903..04c11cf531 100644 --- a/compiler/utils/IOEnv.hs +++ b/compiler/utils/IOEnv.hs @@ -42,6 +42,7 @@ import System.IO.Unsafe ( unsafeInterleaveIO ) import System.IO ( fixIO ) import Control.Monad import MonadUtils +import Control.Applicative (Alternative(..)) ---------------------------------------------------------------------- -- Defining the monad type @@ -150,9 +151,13 @@ unsafeInterleaveM (IOEnv m) = IOEnv (\ env -> unsafeInterleaveIO (m env)) ---------------------------------------------------------------------- --- MonadPlus +-- Alternative/MonadPlus ---------------------------------------------------------------------- +instance MonadPlus IO => Alternative (IOEnv env) where + empty = mzero + (<|>) = mplus + -- For use if the user has imported Control.Monad.Error from MTL -- Requires UndecidableInstances instance MonadPlus IO => MonadPlus (IOEnv env) where |