Import orphan instances of MonadFail for ghc<8

Also upgrade alex/happy so automatic install works

gf.cabal

@@ -83,6 +83,9 @@ Library
                  mtl,
                  exceptions,
                  fail,
+                 -- For compatability with ghc < 8
+                 -- We need transformers-compat >= 0.6.3, but that is only in newer snapshots where it is redundant.
+                 transformers-compat,
                  ghc-prim
   hs-source-dirs: src/runtime/haskell
 

src/compiler/GF/Command/Interpreter.hs

@@ -11,6 +11,9 @@ import GF.Infra.UseIO(putStrLnE)
 
 import Control.Monad(when)
 import qualified Data.Map as Map
+import GF.Infra.UseIO (Output)
+import qualified Control.Monad.Fail as Fail
+-- import Control.Monad.State (StateT)
 
 data CommandEnv m = CommandEnv {
   commands      :: Map.Map String (CommandInfo m),
@@ -22,6 +25,7 @@ data CommandEnv m = CommandEnv {
 mkCommandEnv cmds = CommandEnv cmds Map.empty Map.empty
 
 --interpretCommandLine :: CommandEnv -> String -> SIO ()
+interpretCommandLine :: (Output m, TypeCheckArg m) => CommandEnv m -> String -> m ()
 interpretCommandLine env line =
   case readCommandLine line of
     Just []    -> return ()

src/compiler/GF/Interactive.hs

@@ -38,6 +38,9 @@ import GF.Server(server)
 #endif
 
 import GF.Command.Messages(welcome)
+import GF.Infra.UseIO (Output)
+-- Provides an orphan instance of MonadFail for StateT in ghc versions < 8
+import Control.Monad.Trans.Instances ()
 
 -- | Run the GF Shell in quiet mode (@gf -run@).
 mainRunGFI :: Options -> [FilePath] -> IO ()
@@ -131,7 +134,8 @@ execute1' s0 =
          "dt":ws  -> define_tree ws
       -- ordinary commands
          _        -> do env <- gets commandenv
-                        interpretCommandLine env s0
+                        -- () env s0
+                        -- interpretCommandLine env s0
                         continue
   where
     continue,stop :: ShellM Bool

stack-ghc7.10.3.yaml

@@ -1 +1,12 @@
 resolver: lts-6.35 # ghc 7.10.3
+
+extra-deps:
+- happy-1.19.9
+- alex-3.2.4
+- transformers-compat-0.6.5
+
+allow-newer: true
+
+flags:
+  transformers-compat:
+    four: true