MonadFail: Make backwards-compatible

src/compiler/GF/Compile/GeneratePMCFG.hs

@@ -41,6 +41,7 @@ import Control.Monad
 import Control.Monad.Identity
 --import Control.Exception
 --import Debug.Trace(trace)
+import qualified Control.Monad.Fail as Fail
 
 ----------------------------------------------------------------------
 -- main conversion function
@@ -196,7 +197,7 @@ newtype CnvMonad a = CM {unCM :: SourceGrammar
                               -> ([ProtoFCat],[Symbol])
                               -> Branch b}
 
-instance MonadFail CnvMonad where
+instance Fail.MonadFail CnvMonad where
   fail = bug
 
 instance Applicative CnvMonad where

src/compiler/GF/Compile/TypeCheck/ConcreteNew.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module GF.Compile.TypeCheck.ConcreteNew( checkLType, inferLType ) where
 
 -- The code here is based on the paper:
@@ -19,6 +20,7 @@ import GF.Text.Pretty
 import Data.List (nub, (\\), tails)
 import qualified Data.IntMap as IntMap
 import Data.Maybe(fromMaybe,isNothing)
+import qualified Control.Monad.Fail as Fail
 
 checkLType :: GlobalEnv -> Term -> Type -> Check (Term, Type)
 checkLType ge t ty = runTcM $ do
@@ -647,7 +649,12 @@ instance Monad TcM where
                                 TcOk x ms msgs -> unTcM (g x) ms msgs
                                 TcFail    msgs -> TcFail msgs)
 
-instance MonadFail TcM where
+#if !(MIN_VERSION_base(4,13,0))
+  -- Monad(fail) will be removed in GHC 8.8+
+  fail = Fail.fail
+#endif
+
+instance Fail.MonadFail TcM where
   fail     = tcError . pp
 
 

src/compiler/GF/Compile/Update.hs

@@ -27,9 +27,10 @@ import Data.List
 import qualified Data.Map as Map
 import Control.Monad
 import GF.Text.Pretty
+import qualified Control.Monad.Fail as Fail
 
 -- | combine a list of definitions into a balanced binary search tree
-buildAnyTree :: MonadFail m => ModuleName -> [(Ident,Info)] -> m (Map.Map Ident Info)
+buildAnyTree :: Fail.MonadFail m => ModuleName -> [(Ident,Info)] -> m (Map.Map Ident Info)
 buildAnyTree m = go Map.empty
   where
     go map []         = return map