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Diffstat (limited to 'src/compiler/GF/Data/BacktrackM.hs')
| -rw-r--r-- | src/compiler/GF/Data/BacktrackM.hs | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/src/compiler/GF/Data/BacktrackM.hs b/src/compiler/GF/Data/BacktrackM.hs index 87ea4dc5a..f947b838e 100644 --- a/src/compiler/GF/Data/BacktrackM.hs +++ b/src/compiler/GF/Data/BacktrackM.hs @@ -13,6 +13,7 @@ ----------------------------------------------------------------------------- {-# LANGUAGE Rank2Types, MultiParamTypeClasses, FlexibleInstances #-} +{-# LANGUAGE CPP #-} module GF.Data.BacktrackM ( -- * the backtracking state monad BacktrackM, @@ -32,6 +33,7 @@ import Data.List import Control.Applicative import Control.Monad import Control.Monad.State.Class +import qualified Control.Monad.Fail as Fail ---------------------------------------------------------------------- -- Combining endomorphisms and continuations @@ -70,7 +72,12 @@ instance Monad (BacktrackM s) where BM m >>= k = BM (\c s b -> m (\a s b -> unBM (k a) c s b) s b) where unBM (BM m) = m -instance MonadFail (BacktrackM s) where +#if !(MIN_VERSION_base(4,13,0)) + -- Monad(fail) will be removed in GHC 8.8+ + fail = Fail.fail +#endif + +instance Fail.MonadFail (BacktrackM s) where fail _ = mzero instance Functor (BacktrackM s) where |