GF Shell: refactoring for improved modularity and reusability:

+ Generalize the CommandInfo type by parameterizing it on the monad
  instead of just the environment.
+ Generalize the commands defined in
  GF.Command.{Commands,Commands2,CommonCommands,SourceCommands,HelpCommand}
  to work in any monad that supports the needed operations.
+ Liberate GF.Command.Interpreter from the IO monad.
  Also, move the current PGF from CommandEnv to GFEnv in
  GF.Interactive, making the command interpreter even more generic.
+ Use a state monad to maintain the state of the interpreter in
  GF.{Interactive,Interactive2}.

src/compiler/GF/Infra/UseIO.hs

@@ -34,8 +34,9 @@ import System.CPUTime
 --import System.Cmd
 import Text.Printf
 --import Control.Applicative(Applicative(..))
-import Control.Monad
+import Control.Monad(when,liftM,foldM)
 import Control.Monad.Trans(MonadIO(..))
+import Control.Monad.State(StateT,lift)
 import Control.Exception(evaluate)
 
 --putIfVerb :: MonadIO io => Options -> String -> io ()
@@ -201,6 +202,13 @@ instance Output IOE where
   putStrLnE = liftIO . putStrLnE
   putStrE   = liftIO . putStrE
 -}
+
+instance Output m => Output (StateT s m) where
+  ePutStr = lift . ePutStr
+  ePutStrLn = lift . ePutStrLn
+  putStrE = lift . putStrE
+  putStrLnE = lift . putStrLnE
+
 --putPointE :: Verbosity -> Options -> String -> IO a -> IO a
 putPointE v opts msg act = do
   when (verbAtLeast opts v) $ putStrE msg