FIX #1767 :show documentation claimed too much

[ghc-hetmet.git] / compiler / ghci / InteractiveUI.hs

diff --git a/compiler/ghci/InteractiveUI.hs b/compiler/ghci/InteractiveUI.hs
index 30f1de6..d98b6bc 100644 (file)
--- a/compiler/ghci/InteractiveUI.hs
+++ b/compiler/ghci/InteractiveUI.hs
@@ -82,9 +82,10 @@ import Data.Array
 import Control.Monad as Monad
 import Text.Printf
 import Foreign
 import Control.Monad as Monad
 import Text.Printf
 import Foreign

-import Foreign.C        ( withCStringLen )
+import Foreign.C

 import GHC.Exts                ( unsafeCoerce# )
 import GHC.IOBase      ( IOErrorType(InvalidArgument) )
 import GHC.Exts                ( unsafeCoerce# )
 import GHC.IOBase      ( IOErrorType(InvalidArgument) )

+import GHC.TopHandler

 
 import Data.IORef      ( IORef, readIORef, writeIORef )
 
 
 import Data.IORef      ( IORef, readIORef, writeIORef )
 

@@ -138,6 +139,7 @@ builtin_commands = [
   ("print",     keepGoing printCmd,             Nothing, completeIdentifier),
   ("quit",     quit,                           Nothing, completeNone),
   ("reload",   keepGoing reloadModule,         Nothing, completeNone),
   ("print",     keepGoing printCmd,             Nothing, completeIdentifier),
   ("quit",     quit,                           Nothing, completeNone),
   ("reload",   keepGoing reloadModule,         Nothing, completeNone),

+  ("run",      keepGoing runRun,               Nothing, completeIdentifier),

   ("set",      keepGoing setCmd,               Just flagWordBreakChars, completeSetOptions),
   ("show",     keepGoing showCmd,              Nothing, completeNone),
   ("sprint",    keepGoing sprintCmd,            Nothing, completeIdentifier),
   ("set",      keepGoing setCmd,               Just flagWordBreakChars, completeSetOptions),
   ("show",     keepGoing showCmd,              Nothing, completeNone),
   ("sprint",    keepGoing sprintCmd,            Nothing, completeIdentifier),

@@ -176,7 +178,11 @@ keepGoing :: (String -> GHCi ()) -> (String -> GHCi Bool)
 keepGoing a str = a str >> return False
 
 keepGoingPaths :: ([FilePath] -> GHCi ()) -> (String -> GHCi Bool)
 keepGoing a str = a str >> return False
 
 keepGoingPaths :: ([FilePath] -> GHCi ()) -> (String -> GHCi Bool)

-keepGoingPaths a str = a (toArgs str) >> return False
+keepGoingPaths a str
+ = do case toArgs str of
+          Left err -> io (hPutStrLn stderr err)
+          Right args -> a args
+      return False

 
 shortHelpText :: String
 shortHelpText = "use :? for help.\n"
 
 shortHelpText :: String
 shortHelpText = "use :? for help.\n"

@@ -206,6 +212,7 @@ helpText =
  "   :module [+/-] [*]<mod> ...  set the context for expression evaluation\n" ++
  "   :quit                       exit GHCi\n" ++
  "   :reload                     reload the current module set\n" ++
  "   :module [+/-] [*]<mod> ...  set the context for expression evaluation\n" ++
  "   :quit                       exit GHCi\n" ++
  "   :reload                     reload the current module set\n" ++

+ "   :run function [<arguments> ...] run the function with the given arguments\n" ++

  "   :type <expr>                show the type of <expr>\n" ++
  "   :undef <cmd>                undefine user-defined command :<cmd>\n" ++
  "   :!<command>                 run the shell command <command>\n" ++
  "   :type <expr>                show the type of <expr>\n" ++
  "   :undef <cmd>                undefine user-defined command :<cmd>\n" ++
  "   :!<command>                 run the shell command <command>\n" ++

@@ -221,15 +228,15 @@ helpText =
  "   :delete *                   delete all breakpoints\n" ++
  "   :force <expr>               print <expr>, forcing unevaluated parts\n" ++
  "   :forward                    go forward in the history (after :back)\n" ++
  "   :delete *                   delete all breakpoints\n" ++
  "   :force <expr>               print <expr>, forcing unevaluated parts\n" ++
  "   :forward                    go forward in the history (after :back)\n" ++

- "   :history [<n>]              show the last <n> items in the history (after :trace)\n" ++
+ "   :history [<n>]              after :trace, show the execution history\n" ++

  "   :print [<name> ...]         prints a value without forcing its computation\n" ++
  "   :sprint [<name> ...]        simplifed version of :print\n" ++
  "   :step                       single-step after stopping at a breakpoint\n"++
  "   :step <expr>                single-step into <expr>\n"++
  "   :print [<name> ...]         prints a value without forcing its computation\n" ++
  "   :sprint [<name> ...]        simplifed version of :print\n" ++
  "   :step                       single-step after stopping at a breakpoint\n"++
  "   :step <expr>                single-step into <expr>\n"++

- "   :steplocal                  single-step restricted to the current top level decl.\n"++
+ "   :steplocal                  single-step within the current top-level binding\n"++

  "   :stepmodule                 single-step restricted to the current module\n"++
  "   :trace                      trace after stopping at a breakpoint\n"++
  "   :stepmodule                 single-step restricted to the current module\n"++
  "   :trace                      trace after stopping at a breakpoint\n"++

- "   :trace <expr>               trace into <expr> (remembers breakpoints for :history)\n"++
+ "   :trace <expr>               evaluate <expr> with tracing on (see :history)\n"++

 
  "\n" ++
  " -- Commands for changing settings:\n" ++
 
  "\n" ++
  " -- Commands for changing settings:\n" ++

@@ -260,7 +267,8 @@ helpText =
  "   :show modules               show the currently loaded modules\n" ++
  "   :show packages              show the currently active package flags\n" ++
  "   :show languages             show the currently active language flags\n" ++
  "   :show modules               show the currently loaded modules\n" ++
  "   :show packages              show the currently active package flags\n" ++
  "   :show languages             show the currently active language flags\n" ++

- "   :show <setting>             show anything that can be set with :set (e.g. args)\n" ++
+ "   :show <setting>             show value of <setting>, which is one of\n" ++
+ "                                  [args, prog, prompt, editor, stop]\n" ++

  "\n" 
 
 findEditor :: IO String
  "\n" 
 
 findEditor :: IO String

@@ -274,8 +282,9 @@ findEditor = do
         return ""
 #endif
 
         return ""
 #endif
 

-interactiveUI :: Session -> [(FilePath, Maybe Phase)] -> Maybe String -> IO ()
-interactiveUI session srcs maybe_expr = do
+interactiveUI :: Session -> [(FilePath, Maybe Phase)] -> Maybe [String]
+              -> IO ()
+interactiveUI session srcs maybe_exprs = do

    -- HACK! If we happen to get into an infinite loop (eg the user
    -- types 'let x=x in x' at the prompt), then the thread will block
    -- on a blackhole, and become unreachable during GC.  The GC will
    -- HACK! If we happen to get into an infinite loop (eg the user
    -- types 'let x=x in x' at the prompt), then the thread will block
    -- on a blackhole, and become unreachable during GC.  The GC will

@@ -291,7 +300,7 @@ interactiveUI session srcs maybe_expr = do
     -- Initialise buffering for the *interpreted* I/O system
    initInterpBuffering session
 
     -- Initialise buffering for the *interpreted* I/O system
    initInterpBuffering session
 

-   when (isNothing maybe_expr) $ do
+   when (isNothing maybe_exprs) $ do

         -- Only for GHCi (not runghc and ghc -e):
 
         -- Turn buffering off for the compiled program's stdout/stderr
         -- Only for GHCi (not runghc and ghc -e):
 
         -- Turn buffering off for the compiled program's stdout/stderr

@@ -322,7 +331,7 @@ interactiveUI session srcs maybe_expr = do
 
    default_editor <- findEditor
 
 
    default_editor <- findEditor
 

-   startGHCi (runGHCi srcs maybe_expr)
+   startGHCi (runGHCi srcs maybe_exprs)

         GHCiState{ progname = "<interactive>",
                    args = [],
                    prompt = "%s> ",
         GHCiState{ progname = "<interactive>",
                    args = [],
                    prompt = "%s> ",

@@ -336,7 +345,7 @@ interactiveUI session srcs maybe_expr = do
                    tickarrays = emptyModuleEnv,
                    last_command = Nothing,
                    cmdqueue = [],
                    tickarrays = emptyModuleEnv,
                    last_command = Nothing,
                    cmdqueue = [],

-                   remembered_ctx = Nothing
+                   remembered_ctx = []

                  }
 
 #ifdef USE_READLINE
                  }
 
 #ifdef USE_READLINE

@@ -345,8 +354,8 @@ interactiveUI session srcs maybe_expr = do
 
    return ()
 
 
    return ()
 

-runGHCi :: [(FilePath, Maybe Phase)] -> Maybe String -> GHCi ()
-runGHCi paths maybe_expr = do
+runGHCi :: [(FilePath, Maybe Phase)] -> Maybe [String] -> GHCi ()
+runGHCi paths maybe_exprs = do

   let read_dot_files = not opt_IgnoreDotGhci
 
   when (read_dot_files) $ do
   let read_dot_files = not opt_IgnoreDotGhci
 
   when (read_dot_files) $ do

@@ -384,7 +393,7 @@ runGHCi paths maybe_expr = do
   when (not (null paths)) $ do
      ok <- ghciHandle (\e -> do showException e; return Failed) $
                 loadModule paths
   when (not (null paths)) $ do
      ok <- ghciHandle (\e -> do showException e; return Failed) $
                 loadModule paths

-     when (isJust maybe_expr && failed ok) $
+     when (isJust maybe_exprs && failed ok) $

         io (exitWith (ExitFailure 1))
 
   -- if verbosity is greater than 0, or we are connected to a
         io (exitWith (ExitFailure 1))
 
   -- if verbosity is greater than 0, or we are connected to a

@@ -393,7 +402,7 @@ runGHCi paths maybe_expr = do
   dflags <- getDynFlags
   let show_prompt = verbosity dflags > 0 || is_tty
 
   dflags <- getDynFlags
   let show_prompt = verbosity dflags > 0 || is_tty
 

-  case maybe_expr of
+  case maybe_exprs of

         Nothing ->
           do
 #if defined(mingw32_HOST_OS)
         Nothing ->
           do
 #if defined(mingw32_HOST_OS)

@@ -409,15 +418,25 @@ runGHCi paths maybe_expr = do
 #endif
             -- enter the interactive loop
             interactiveLoop is_tty show_prompt
 #endif
             -- enter the interactive loop
             interactiveLoop is_tty show_prompt

-        Just expr -> do
+        Just exprs -> do

             -- just evaluate the expression we were given
             -- just evaluate the expression we were given

-            runCommandEval expr
-            return ()
+            enqueueCommands exprs
+            let handle e = do st <- getGHCiState
+                                   -- Jump through some hoops to get the
+                                   -- current progname in the exception text:
+                                   -- <progname>: <exception>
+                              io $ withProgName (progname st)
+                                   -- The "fast exit" part just calls exit()
+                                   -- directly instead of doing an orderly
+                                   -- runtime shutdown, otherwise the main
+                                   -- GHCi thread will complain about being
+                                   -- interrupted.
+                                 $ topHandlerFastExit e
+            runCommands' handle (return Nothing)

 
   -- and finally, exit
   io $ do when (verbosity dflags > 0) $ putStrLn "Leaving GHCi."
 
 
   -- and finally, exit
   io $ do when (verbosity dflags > 0) $ putStrLn "Leaving GHCi."
 

-

 interactiveLoop :: Bool -> Bool -> GHCi ()
 interactiveLoop is_tty show_prompt =
   -- Ignore ^C exceptions caught here
 interactiveLoop :: Bool -> Bool -> GHCi ()
 interactiveLoop is_tty show_prompt =
   -- Ignore ^C exceptions caught here

@@ -588,14 +607,18 @@ queryQueue = do
                return (Just c)
 
 runCommands :: GHCi (Maybe String) -> GHCi ()
                return (Just c)
 
 runCommands :: GHCi (Maybe String) -> GHCi ()

-runCommands getCmd = do
+runCommands = runCommands' handler
+
+runCommands' :: (Exception -> GHCi Bool) -- Exception handler
+             -> GHCi (Maybe String) -> GHCi ()
+runCommands' eh getCmd = do

   mb_cmd <- noSpace queryQueue
   mb_cmd <- maybe (noSpace getCmd) (return . Just) mb_cmd
   case mb_cmd of 
     Nothing -> return ()
     Just c  -> do
   mb_cmd <- noSpace queryQueue
   mb_cmd <- maybe (noSpace getCmd) (return . Just) mb_cmd
   case mb_cmd of 
     Nothing -> return ()
     Just c  -> do

-      b <- ghciHandle handler (doCommand c)
-      if b then return () else runCommands getCmd
+      b <- ghciHandle eh (doCommand c)
+      if b then return () else runCommands' eh getCmd

   where
     noSpace q = q >>= maybe (return Nothing)
                             (\c->case removeSpaces c of 
   where
     noSpace q = q >>= maybe (return Nothing)
                             (\c->case removeSpaces c of 

@@ -636,24 +659,6 @@ enqueueCommands cmds = do
   setGHCiState st{ cmdqueue = cmds ++ cmdqueue st }
 
 
   setGHCiState st{ cmdqueue = cmds ++ cmdqueue st }
 
 

--- This version is for the GHC command-line option -e.  The only difference
--- from runCommand is that it catches the ExitException exception and
--- exits, rather than printing out the exception.
-runCommandEval :: String -> GHCi Bool
-runCommandEval c = ghciHandle handleEval (doCommand c)
-  where 
-    handleEval (ExitException code) = io (exitWith code)
-    handleEval e                    = do handler e
-                                        io (exitWith (ExitFailure 1))
-
-    doCommand (':' : command) = specialCommand command
-    doCommand stmt
-       = do r <- runStmt stmt GHC.RunToCompletion
-           case r of 
-               False -> io (exitWith (ExitFailure 1))
-                 -- failure to run the command causes exit(1) for ghc -e.
-               _       -> return True
-

 runStmt :: String -> SingleStep -> GHCi Bool
 runStmt stmt step
  | null (filter (not.isSpace) stmt) = return False
 runStmt :: String -> SingleStep -> GHCi Bool
 runStmt stmt step
  | null (filter (not.isSpace) stmt) = return False

@@ -851,9 +856,22 @@ pprInfo pefas (thing, fixity, insts)
        | otherwise                = ppr fix <+> ppr (GHC.getName thing)
 
 runMain :: String -> GHCi ()
        | otherwise                = ppr fix <+> ppr (GHC.getName thing)
 
 runMain :: String -> GHCi ()

-runMain args = do
-  let ss = concat $ intersperse "," (map (\ s -> ('"':s)++"\"") (toArgs args))
-  enqueueCommands  ['[': ss ++ "] `System.Environment.withArgs` main"]
+runMain s = case toArgs s of
+            Left err   -> io (hPutStrLn stderr err)
+            Right args ->
+                do dflags <- getDynFlags
+                   case mainFunIs dflags of
+                       Nothing -> doWithArgs args "main"
+                       Just f  -> doWithArgs args f
+
+runRun :: String -> GHCi ()
+runRun s = case toCmdArgs s of
+           Left err          -> io (hPutStrLn stderr err)
+           Right (cmd, args) -> doWithArgs args cmd
+
+doWithArgs :: [String] -> String -> GHCi ()
+doWithArgs args cmd = enqueueCommands ["System.Environment.withArgs " ++
+                                       show args ++ " (" ++ cmd ++ ")"]

 
 addModule :: [FilePath] -> GHCi ()
 addModule files = do
 
 addModule :: [FilePath] -> GHCi ()
 addModule files = do

@@ -881,7 +899,7 @@ changeDirectory dir = do
   prev_context <- io $ GHC.getContext session
   io (GHC.setTargets session [])
   io (GHC.load session LoadAllTargets)
   prev_context <- io $ GHC.getContext session
   io (GHC.setTargets session [])
   io (GHC.load session LoadAllTargets)

-  setContextAfterLoad session prev_context []
+  setContextAfterLoad session prev_context False []

   io (GHC.workingDirectoryChanged session)
   dir <- expandPath dir
   io (setCurrentDirectory dir)
   io (GHC.workingDirectoryChanged session)
   dir <- expandPath dir
   io (setCurrentDirectory dir)

@@ -1063,45 +1081,14 @@ afterLoad ok session retain_context prev_context = do
       loaded_mod_names = map GHC.moduleName loaded_mods
   modulesLoadedMsg ok loaded_mod_names
 
       loaded_mod_names = map GHC.moduleName loaded_mods
   modulesLoadedMsg ok loaded_mod_names
 

-  st <- getGHCiState
-  if not retain_context
-    then do
-        setGHCiState st{ remembered_ctx = Nothing }
-        setContextAfterLoad session prev_context loaded_mod_summaries
-    else do
-        -- figure out which modules we can keep in the context, which we
-        -- have to put back, and which we have to remember because they
-        -- are (temporarily) unavailable.  See ghci.prog009, #1873, #1360
-        let (as,bs) = prev_context
-            as1 = filter isHomeModule as -- package modules are kept anyway
-            bs1 = filter isHomeModule bs
-            (as_ok, as_bad) = partition (`elem` loaded_mods) as1
-            (bs_ok, bs_bad) = partition (`elem` loaded_mods) bs1
-            (rem_as, rem_bs) = fromMaybe ([],[]) (remembered_ctx st)
-            (rem_as_ok, rem_as_bad) = partition (`elem` loaded_mods) rem_as
-            (rem_bs_ok, rem_bs_bad) = partition (`elem` loaded_mods) rem_bs
-            as' = nub (as_ok++rem_as_ok)
-            bs' = nub (bs_ok++rem_bs_ok)
-            rem_as' = nub (rem_as_bad ++ as_bad)
-            rem_bs' = nub (rem_bs_bad ++ bs_bad)
-
-         -- Put back into the context any modules that we previously had
-         -- to drop because they weren't available (rem_as_ok, rem_bs_ok).
-        setContextKeepingPackageModules session prev_context (as',bs')
-
-         -- If compilation failed, remember any modules that we are unable
-         -- to load, so that we can put them back in the context in the future.
-        case ok of
-         Succeeded -> setGHCiState st{ remembered_ctx = Nothing }
-         Failed    -> setGHCiState st{ remembered_ctx = Just (rem_as',rem_bs') }
-
-
-
-setContextAfterLoad :: Session -> ([Module],[Module]) -> [GHC.ModSummary] -> GHCi ()
-setContextAfterLoad session prev [] = do
+  setContextAfterLoad session prev_context retain_context loaded_mod_summaries
+
+
+setContextAfterLoad :: Session -> ([Module],[Module]) -> Bool -> [GHC.ModSummary] -> GHCi ()
+setContextAfterLoad session prev keep_ctxt [] = do

   prel_mod <- getPrelude
   prel_mod <- getPrelude

-  setContextKeepingPackageModules session prev ([], [prel_mod])
-setContextAfterLoad session prev ms = do
+  setContextKeepingPackageModules session prev keep_ctxt ([], [prel_mod])
+setContextAfterLoad session prev keep_ctxt ms = do

   -- load a target if one is available, otherwise load the topmost module.
   targets <- io (GHC.getTargets session)
   case [ m | Just m <- map (findTarget ms) targets ] of
   -- load a target if one is available, otherwise load the topmost module.
   targets <- io (GHC.getTargets session)
   case [ m | Just m <- map (findTarget ms) targets ] of

@@ -1125,23 +1112,31 @@ setContextAfterLoad session prev ms = do
 
    load_this summary | m <- GHC.ms_mod summary = do
        b <- io (GHC.moduleIsInterpreted session m)
 
    load_this summary | m <- GHC.ms_mod summary = do
        b <- io (GHC.moduleIsInterpreted session m)

-       if b then setContextKeepingPackageModules session prev ([m], [])
+       if b then setContextKeepingPackageModules session prev keep_ctxt ([m], [])

                     else do
                 prel_mod <- getPrelude
                     else do
                 prel_mod <- getPrelude

-                setContextKeepingPackageModules session prev ([],[prel_mod,m])
+                setContextKeepingPackageModules session prev keep_ctxt ([],[prel_mod,m])

 
 -- | Keep any package modules (except Prelude) when changing the context.
 setContextKeepingPackageModules
         :: Session
         -> ([Module],[Module])          -- previous context
 
 -- | Keep any package modules (except Prelude) when changing the context.
 setContextKeepingPackageModules
         :: Session
         -> ([Module],[Module])          -- previous context

+        -> Bool                         -- re-execute :module commands

         -> ([Module],[Module])          -- new context
         -> GHCi ()
         -> ([Module],[Module])          -- new context
         -> GHCi ()

-setContextKeepingPackageModules session prev_context (as,bs) = do
+setContextKeepingPackageModules session prev_context keep_ctxt (as,bs) = do

   let (_,bs0) = prev_context
   prel_mod <- getPrelude
   let pkg_modules = filter (\p -> not (isHomeModule p) && p /= prel_mod) bs0
   let bs1 = if null as then nub (prel_mod : bs) else bs
   io $ GHC.setContext session as (nub (bs1 ++ pkg_modules))
   let (_,bs0) = prev_context
   prel_mod <- getPrelude
   let pkg_modules = filter (\p -> not (isHomeModule p) && p /= prel_mod) bs0
   let bs1 = if null as then nub (prel_mod : bs) else bs
   io $ GHC.setContext session as (nub (bs1 ++ pkg_modules))

+  if keep_ctxt
+     then do
+          st <- getGHCiState
+          mapM_ (playCtxtCmd False) (remembered_ctx st)
+     else do
+          st <- getGHCiState
+          setGHCiState st{ remembered_ctx = [] }

 
 isHomeModule :: Module -> Bool
 isHomeModule mod = GHC.modulePackageId mod == mainPackageId
 
 isHomeModule :: Module -> Bool
 isHomeModule mod = GHC.modulePackageId mod == mainPackageId

@@ -1300,60 +1295,65 @@ browseModule bang modl exports_only = do
 
 setContext :: String -> GHCi ()
 setContext str
 
 setContext :: String -> GHCi ()
 setContext str

-  | all sensible mods = fn mods
+  | all sensible strs = do
+       playCtxtCmd True (cmd, as, bs)
+       st <- getGHCiState
+       setGHCiState st{ remembered_ctx = remembered_ctx st ++ [(cmd,as,bs)] }

   | otherwise = throwDyn (CmdLineError "syntax:  :module [+/-] [*]M1 ... [*]Mn")
   where
   | otherwise = throwDyn (CmdLineError "syntax:  :module [+/-] [*]M1 ... [*]Mn")
   where

-    (fn, mods) = case str of 
-                       '+':stuff -> (addToContext,      words stuff)
-                       '-':stuff -> (removeFromContext, words stuff)
-                       stuff     -> (newContext,        words stuff) 
+    (cmd, strs, as, bs) =
+        case str of 
+                '+':stuff -> rest AddModules stuff
+                '-':stuff -> rest RemModules stuff
+                stuff     -> rest SetContext stuff
+
+    rest cmd stuff = (cmd, strs, as, bs)
+       where strs = words stuff
+             (as,bs) = partitionWith starred strs

 
     sensible ('*':m) = looksLikeModuleName m
     sensible m       = looksLikeModuleName m
 
 
     sensible ('*':m) = looksLikeModuleName m
     sensible m       = looksLikeModuleName m
 

-separate :: Session -> [String] -> [Module] -> [Module] 
-        -> GHCi ([Module],[Module])
-separate _       []             as bs = return (as,bs)
-separate session (('*':str):ms) as bs = do
-  m <- wantInterpretedModule str
-  separate session ms (m:as) bs
-separate session (str:ms) as bs = do
-  m <- lookupModule str
-  separate session ms as (m:bs)
-
-newContext :: [String] -> GHCi ()
-newContext strs = do
-  s <- getSession
-  (as,bs) <- separate s strs [] []
-  prel_mod <- getPrelude
-  let bs' = if null as && prel_mod `notElem` bs then prel_mod:bs else bs
-  io $ GHC.setContext s as bs'
-
+    starred ('*':m) = Left m
+    starred m       = Right m

 
 

-addToContext :: [String] -> GHCi ()
-addToContext strs = do
-  s <- getSession
-  (as,bs) <- io $ GHC.getContext s
-
-  (new_as,new_bs) <- separate s strs [] []
-
-  let as_to_add = new_as \\ (as ++ bs)
-      bs_to_add = new_bs \\ (as ++ bs)
-
-  io $ GHC.setContext s (as ++ as_to_add) (bs ++ bs_to_add)
-
-
-removeFromContext :: [String] -> GHCi ()
-removeFromContext strs = do
-  s <- getSession
-  (as,bs) <- io $ GHC.getContext s
-
-  (as_to_remove,bs_to_remove) <- separate s strs [] []
-
-  let as' = as \\ (as_to_remove ++ bs_to_remove)
-      bs' = bs \\ (as_to_remove ++ bs_to_remove)
-
-  io $ GHC.setContext s as' bs'
+playCtxtCmd :: Bool -> (CtxtCmd, [String], [String]) -> GHCi ()
+playCtxtCmd fail (cmd, as, bs)
+  = do
+    s <- getSession
+    (as',bs') <- do_checks fail
+    (prev_as,prev_bs) <- io $ GHC.getContext s
+    (new_as, new_bs) <-
+      case cmd of
+        SetContext -> do
+          prel_mod <- getPrelude
+          let bs'' = if null as && prel_mod `notElem` bs' then prel_mod:bs'
+                                                          else bs'
+          return (as',bs'')
+        AddModules -> do
+          let as_to_add = as' \\ (prev_as ++ prev_bs)
+              bs_to_add = bs' \\ (prev_as ++ prev_bs)
+          return (prev_as ++ as_to_add, prev_bs ++ bs_to_add)
+        RemModules -> do
+          let new_as = prev_as \\ (as' ++ bs')
+              new_bs = prev_bs \\ (as' ++ bs')
+          return (new_as, new_bs)
+    io $ GHC.setContext s new_as new_bs
+  where
+    do_checks True = do
+      as' <- mapM wantInterpretedModule as
+      bs' <- mapM lookupModule bs
+      return (as',bs')
+    do_checks False = do
+      as' <- mapM (trymaybe . wantInterpretedModule) as
+      bs' <- mapM (trymaybe . lookupModule) bs
+      return (catMaybes as', catMaybes bs')
+
+    trymaybe m = do
+        r <- ghciTry m
+        case r of
+          Left _  -> return Nothing
+          Right a -> return (Just a)

 
 ----------------------------------------------------------------------------
 -- Code for `:set'
 
 ----------------------------------------------------------------------------
 -- Code for `:set'

@@ -1398,27 +1398,32 @@ setCmd ""
                 ,Opt_PrintEvldWithShow
                 ] 
 setCmd str
                 ,Opt_PrintEvldWithShow
                 ] 
 setCmd str

-  = case toArgs str of
-       ("args":args) -> setArgs args
-       ("prog":prog) -> setProg prog
-        ("prompt":_)  -> setPrompt (after 6)
-        ("editor":_)  -> setEditor (after 6)
-        ("stop":_)    -> setStop (after 4)
-       wds -> setOptions wds
-   where after n = dropWhile isSpace $ drop n $ dropWhile isSpace str
-
-setArgs, setProg, setOptions :: [String] -> GHCi ()
-setEditor, setStop, setPrompt :: String -> GHCi ()
+  = case getCmd str of
+    Right ("args",   rest) ->
+        case toArgs rest of
+            Left err -> io (hPutStrLn stderr err)
+            Right args -> setArgs args
+    Right ("prog",   rest) ->
+        case toArgs rest of
+            Right [prog] -> setProg prog
+            _ -> io (hPutStrLn stderr "syntax: :set prog <progname>")
+    Right ("prompt", rest) -> setPrompt $ dropWhile isSpace rest
+    Right ("editor", rest) -> setEditor $ dropWhile isSpace rest
+    Right ("stop",   rest) -> setStop   $ dropWhile isSpace rest
+    _ -> case toArgs str of
+         Left err -> io (hPutStrLn stderr err)
+         Right wds -> setOptions wds
+
+setArgs, setOptions :: [String] -> GHCi ()
+setProg, setEditor, setStop, setPrompt :: String -> GHCi ()

 
 setArgs args = do
   st <- getGHCiState
   setGHCiState st{ args = args }
 
 
 setArgs args = do
   st <- getGHCiState
   setGHCiState st{ args = args }
 

-setProg [prog] = do
+setProg prog = do

   st <- getGHCiState
   setGHCiState st{ progname = prog }
   st <- getGHCiState
   setGHCiState st{ progname = prog }

-setProg _ = do
-  io (hPutStrLn stderr "syntax: :set prog <progname>")

 
 setEditor cmd = do
   st <- getGHCiState
 
 setEditor cmd = do
   st <- getGHCiState

@@ -1480,7 +1485,7 @@ newDynFlags minus_opts = do
         io (GHC.load session LoadAllTargets)
         io (linkPackages dflags new_pkgs)
         -- package flags changed, we can't re-use any of the old context
         io (GHC.load session LoadAllTargets)
         io (linkPackages dflags new_pkgs)
         -- package flags changed, we can't re-use any of the old context

-        setContextAfterLoad session ([],[]) []
+        setContextAfterLoad session ([],[]) False []

       return ()
 
 
       return ()
 
 

@@ -1553,7 +1558,8 @@ showCmd str = do
         ["context"]  -> showContext
         ["packages"]  -> showPackages
         ["languages"]  -> showLanguages
         ["context"]  -> showContext
         ["packages"]  -> showPackages
         ["languages"]  -> showLanguages

-       _ -> throwDyn (CmdLineError "syntax:  :show [args|prog|prompt|editor|stop|modules|bindings|breaks|context]")
+       _ -> throwDyn (CmdLineError ("syntax:  :show [ args | prog | prompt | editor | stop | modules | bindings\n"++
+                                     "               | breaks | context | packages | languages ]"))

 
 showModules :: GHCi ()
 showModules = do
 
 showModules :: GHCi ()
 showModules = do

@@ -1811,6 +1817,8 @@ ghciHandle h (GHCi m) = GHCi $ \s ->
 ghciUnblock :: GHCi a -> GHCi a
 ghciUnblock (GHCi a) = GHCi $ \s -> Exception.unblock (a s)
 
 ghciUnblock :: GHCi a -> GHCi a
 ghciUnblock (GHCi a) = GHCi $ \s -> Exception.unblock (a s)
 

+ghciTry :: GHCi a -> GHCi (Either Exception a)
+ghciTry (GHCi m) = GHCi $ \s -> Exception.try (m s) 

 
 -- ----------------------------------------------------------------------------
 -- Utils
 
 -- ----------------------------------------------------------------------------
 -- Utils

@@ -2336,4 +2344,3 @@ setBreakFlag :: Bool -> GHC.BreakArray -> Int -> IO Bool
 setBreakFlag toggle array index
    | toggle    = GHC.setBreakOn array index 
    | otherwise = GHC.setBreakOff array index
 setBreakFlag toggle array index
    | toggle    = GHC.setBreakOn array index 
    | otherwise = GHC.setBreakOff array index

-