Merge pull request #148 from anka-213/fix-ghc-7.10-build

Fix ghc-7.10 build

gf.cabal

@@ -85,6 +85,8 @@ library
 
   if impl(ghc<8.0)
     build-depends:
+      -- We need this in order for ghc-7.10 to build
+      transformers-compat >= 0.6.3 && < 0.7,
       fail >= 4.9.0 && < 4.10
 
   hs-source-dirs: src/runtime/haskell

src/compiler/GF/Interactive.hs

@@ -38,6 +38,10 @@ import GF.Server(server)
 #endif
 
 import GF.Command.Messages(welcome)
+#if !(MIN_VERSION_base(4,9,0))
+-- Needed to make it compile on GHC < 8
+import Control.Monad.Trans.Instances ()
+#endif
 
 -- | Run the GF Shell in quiet mode (@gf -run@).
 mainRunGFI :: Options -> [FilePath] -> IO ()

src/tools/c/GFCC/ErrM.hs

@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveFunctor #-}
 -- BNF Converter: Error Monad
 -- Copyright (C) 2004  Author:  Aarne Ranta
 
@@ -6,12 +8,17 @@ module GFCC.ErrM where
 
 -- Control.Monad.Fail import will become redundant in GHC 8.8+
 import qualified Control.Monad.Fail as Fail
+import Control.Monad (ap)
 
 
 -- the Error monad: like Maybe type with error msgs
 
 data Err a = Ok a | Bad String
-  deriving (Read, Show, Eq)
+  deriving (Read, Show, Eq, Functor)
+
+instance Applicative Err where
+  pure = Ok
+  (<*>) = ap
 
 instance Monad Err where
   return      = Ok