1 files changed, 9 insertions, 0 deletions
diff --git a/src/compiler/GF/Data/BacktrackM.hs b/src/compiler/GF/Data/BacktrackM.hs
index 4e84022f4..f5ae63997 100644
--- a/src/compiler/GF/Data/BacktrackM.hs
+++ b/src/compiler/GF/Data/BacktrackM.hs
@@ -29,6 +29,7 @@ module GF.Data.BacktrackM (
 		  ) where
 
 import Data.List
+import Control.Applicative
 import Control.Monad
 import Control.Monad.State.Class
 
@@ -60,6 +61,10 @@ foldFinalStates f b (BM m) s = m (\x s b -> f s b) s b
 finalStates :: BacktrackM s () -> s -> [s]
 finalStates bm = map fst . runBM bm
 
+instance Applicative (BacktrackM s) where
+    pure = return
+    (<*>) = ap
+
 instance Monad (BacktrackM s) where
     return a   = BM (\c s b -> c a s b)
     BM m >>= k = BM (\c s b -> m (\a s b -> unBM (k a) c s b) s b)
@@ -69,6 +74,10 @@ instance Monad (BacktrackM s) where
 instance Functor (BacktrackM s) where
     fmap f (BM m) = BM (\c s b -> m (\a s b -> c (f a) s b) s b)
 
+instance Alternative (BacktrackM s) where
+   empty = mzero
+   (<|>) = mplus
+
 instance MonadPlus (BacktrackM s) where
     mzero                 = BM (\c s b -> b)
     (BM f) `mplus` (BM g) = BM (\c s b -> g c s $! f c s b)