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/Data/Utilities.hs

@@ -16,7 +16,7 @@ module GF.Data.Utilities(module GF.Data.Utilities, module PGF.Utilities) where
 
 import Data.Maybe
 import Data.List
-import Control.Monad (MonadPlus(..),liftM)
+import Control.Monad (MonadPlus(..),liftM,when)
 import PGF.Utilities
 
 -- * functions on lists
@@ -136,6 +136,10 @@ mapBoth = map . apBoth
 whenMP :: MonadPlus m => Bool -> a -> m a
 whenMP b x = if b then return x else mzero
 
+whenM bm m = flip when m =<< bm
+
+repeatM m = whenM m (repeatM m)
+
 -- * functions on Maybes
 
 -- | Returns true if the argument is Nothing or Just []