Optparse GHC 7.4 compatibility

ghc-mod.cabal

@@ -192,6 +192,7 @@ Executable ghc-mod
                       , GHCMod.Options.Commands
                       , GHCMod.Version
                       , GHCMod.Options.DocUtils
+                      , GHCMod.Options.GapUtils
   GHC-Options:          -Wall -fno-warn-deprecations -threaded
   Default-Extensions:   ConstraintKinds, FlexibleContexts
   HS-Source-Dirs:       src

src/GHCMod/Options/Commands.hs

@@ -3,8 +3,8 @@ module GHCMod.Options.Commands where
 import Options.Applicative
 import Options.Applicative.Types
 import Language.Haskell.GhcMod.Types
-import Text.Read (readMaybe)
 import GHCMod.Options.DocUtils
+import GHCMod.Options.GapUtils
 
 type Symbol = String
 type Expr = String
@@ -37,11 +37,6 @@ data GhcModCommands =
   | CmdAuto FilePath Point
   | CmdRefine FilePath Point Expr
 
-int :: ReadM Int
-int = do
-  v <- readerAsk
-  maybe (readerError $ "Not a number \"" ++ v ++ "\"") return $ readMaybe v
-
 commandsSpec :: Parser GhcModCommands
 commandsSpec =
   hsubparser (
@@ -228,3 +223,8 @@ autoArgSpec = locArgSpec CmdAuto
 splitArgSpec = locArgSpec CmdSplit
 sigArgSpec = locArgSpec CmdSig
 refineArgSpec = locArgSpec CmdRefine <*> strArg "SYMBOL"
+
+int :: ReadM Int
+int = do
+  v <- readerAsk
+  maybe (readerError $ "Not a number \"" ++ v ++ "\"") return $ readMaybe v

src/GHCMod/Options/GapUtils.hs

@@ -0,0 +1,12 @@
+{-# LANGUAGE CPP #-}
+
+module GHCMod.Options.GapUtils (
+  readMaybe
+) where
+
+#if __GLASGOW_HASKELL__ >= 706
+import Text.Read (readMaybe)
+#else
+readMaybe :: Read a => String -> Maybe a
+readMaybe = Just . read
+#endif