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Diffstat (limited to 'compiler/utils/ListT.hs')
| -rw-r--r-- | compiler/utils/ListT.hs | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/compiler/utils/ListT.hs b/compiler/utils/ListT.hs index 2b81db1ed4..c16701419d 100644 --- a/compiler/utils/ListT.hs +++ b/compiler/utils/ListT.hs @@ -29,9 +29,12 @@ module ListT ( fold ) where +import GhcPrelude + import Control.Applicative import Control.Monad +import Control.Monad.Fail as MonadFail ------------------------------------------------------------------------- -- | A monad transformer for performing backtracking computations @@ -64,6 +67,9 @@ instance Alternative (ListT f) where instance Monad (ListT m) where m >>= f = ListT $ \sk fk -> unListT m (\a fk' -> unListT (f a) sk fk') fk + fail = MonadFail.fail + +instance MonadFail (ListT m) where fail _ = ListT $ \_ fk -> fk instance MonadPlus (ListT m) where |