X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=ghc%2Fcompiler%2Fghci%2FInteractiveUI.hs;h=533c295627362a35800d64bf986e382ee352b394;hb=432c57562b861f9d00bc70eea0ba393f8847c92e;hp=2ac225a78425a4db9589ff540b7a1442ec3c7961;hpb=972d6442ee3a6ee0a5fa20655d882e0041646892;p=ghc-hetmet.git

diff --git a/ghc/compiler/ghci/InteractiveUI.hs b/ghc/compiler/ghci/InteractiveUI.hs
index 2ac225a..533c295 100644
--- a/ghc/compiler/ghci/InteractiveUI.hs
+++ b/ghc/compiler/ghci/InteractiveUI.hs
@@ -1,20 +1,21 @@
+{-# OPTIONS -#include "Linker.h" -#include "SchedAPI.h" #-}
 -----------------------------------------------------------------------------
--- $Id: InteractiveUI.hs,v 1.75 2001/06/15 08:29:57 simonpj Exp $
+-- $Id: InteractiveUI.hs,v 1.104 2002/01/03 17:05:50 sewardj Exp $
 --
 -- GHC Interactive User Interface
 --
 -- (c) The GHC Team 2000
 --
 -----------------------------------------------------------------------------
-
-{-# OPTIONS -#include "Linker.h" #-}
 module InteractiveUI ( interactiveUI, ghciWelcomeMsg ) where
 
 #include "../includes/config.h"
 #include "HsVersions.h"
 
+import Packages
 import CompManager
-import HscTypes		( GhciMode(..) )
+import HscTypes		( TyThing(..) )
+import MkIface
 import ByteCodeLink
 import DriverFlags
 import DriverState
@@ -22,10 +23,19 @@ import DriverUtil
 import Linker
 import Finder		( flushPackageCache )
 import Util
-import Name		( Name )
+import Id		( isRecordSelector, recordSelectorFieldLabel, 
+			  isDataConWrapId, idName )
+import Class		( className )
+import TyCon		( tyConName, tyConClass_maybe, isPrimTyCon )
+import FieldLabel	( fieldLabelTyCon )
+import SrcLoc		( isGoodSrcLoc )
+import Name		( Name, isHomePackageName, nameSrcLoc, nameOccName,
+			  NamedThing(..) )
+import OccName		( isSymOcc )
+import BasicTypes	( defaultFixity )
 import Outputable
 import CmdLineOpts	( DynFlag(..), getDynFlags, saveDynFlags, restoreDynFlags, dopt_unset )
-import Panic		( GhcException(..) )
+import Panic		( GhcException(..), showGhcException )
 import Config
 
 #ifndef mingw32_TARGET_OS
@@ -37,7 +47,9 @@ import Dynamic
 #if HAVE_READLINE_HEADERS && HAVE_READLINE_LIBS
 import Readline 
 #endif
+import Concurrent
 import IOExts
+import SystemExts
 
 import Numeric
 import List
@@ -46,7 +58,7 @@ import CPUTime
 import Directory
 import IO
 import Char
-import Monad 		( when )
+import Monad 		( when, join )
 
 import PrelGHC 		( unsafeCoerce# )
 import Foreign		( nullPtr )
@@ -70,10 +82,11 @@ builtin_commands = [
   ("def",	keepGoing defineMacro),
   ("help",	keepGoing help),
   ("?",		keepGoing help),
+  ("info",      keepGoing info),
   ("load",	keepGoing loadModule),
   ("module",	keepGoing setContext),
   ("reload",	keepGoing reloadModule),
-  ("set",	keepGoing setOptions),
+  ("set",	keepGoing setCmd),
   ("type",	keepGoing typeOfExpr),
   ("unset",	keepGoing unsetOptions),
   ("undef",     keepGoing undefineMacro),
@@ -87,15 +100,19 @@ shortHelpText = "use :? for help.\n"
 
 helpText = "\ 
 \ Commands available from the prompt:\n\ 
-\\  
+\\
 \   <stmt>		   evaluate/run <stmt>\n\ 
+\   :add <filename> ...    add module(s) to the current target set\n\ 
 \   :cd <dir>		   change directory to <dir>\n\ 
 \   :def <cmd> <expr>      define a command :<cmd>\n\ 
 \   :help, :?		   display this list of commands\n\ 
-\   :load <filename>       load a module (and its dependents)\n\ 
+\   :info [<name> ...]     display information about the given names\n\ 
+\   :load <filename> ...   load module(s) and their dependents\n\ 
 \   :module <mod>	   set the context for expression evaluation to <mod>\n\ 
 \   :reload		   reload the current module set\n\ 
 \   :set <option> ...	   set options\n\ 
+\   :set args <arg> ...	   set the arguments returned by System.getArgs\n\ 
+\   :set prog <progname>   set the value returned by System.getProgName\n\ 
 \   :undef <cmd> 	   undefine user-defined command :<cmd>\n\ 
 \   :type <expr>	   show the type of <expr>\n\ 
 \   :unset <option> ...	   unset options\n\ 
@@ -110,10 +127,9 @@ helpText = "\
 \    -<flags>		most GHC command line flags can also be set here\n\ 
 \                         (eg. -v2, -fglasgow-exts, etc.)\n\ 
 \"
- --ToDo   :add <filename>     add a module to the current set\n\ 
 
-interactiveUI :: CmState -> Maybe FilePath -> [LibrarySpec] -> IO ()
-interactiveUI cmstate mod cmdline_libs = do
+interactiveUI :: CmState -> [FilePath] -> [LibrarySpec] -> IO ()
+interactiveUI cmstate paths cmdline_libs = do
    hFlush stdout
    hSetBuffering stdout NoBuffering
 
@@ -122,18 +138,15 @@ interactiveUI cmstate mod cmdline_libs = do
    initLinker
    linkPackages cmdline_libs pkgs
 
-   (cmstate, ok, mods) <-
-   	case mod of
-	     Nothing  -> return (cmstate, True, [])
-	     Just m -> cmLoadModule cmstate m
-
-#if HAVE_READLINE_HEADERS && HAVE_READLINE_LIBS
-   Readline.initialize
-#endif
-
    dflags <- getDynFlags
 
    (cmstate, maybe_hval) 
+	<- cmCompileExpr cmstate dflags "IO.hSetBuffering IO.stdout IO.NoBuffering Prelude.>> IO.hSetBuffering IO.stderr IO.NoBuffering"
+   case maybe_hval of
+	Just hval -> unsafeCoerce# hval :: IO ()
+	_ -> panic "interactiveUI:buffering"
+
+   (cmstate, maybe_hval)
 	<- cmCompileExpr cmstate dflags "IO.hFlush PrelHandle.stderr"
    case maybe_hval of
 	Just hval -> writeIORef flush_stderr (unsafeCoerce# hval :: IO ())
@@ -145,39 +158,73 @@ interactiveUI cmstate mod cmdline_libs = do
 	Just hval -> writeIORef flush_stdout (unsafeCoerce# hval :: IO ())
 	_ -> panic "interactiveUI:stdout"
 
-   startGHCi runGHCi GHCiState{ target = mod,
-			        cmstate = cmstate,
-			        options = [] }
+#if HAVE_READLINE_HEADERS && HAVE_READLINE_LIBS
+   Readline.initialize
+#endif
+
+   startGHCi (runGHCi paths) 
+	GHCiState{ progname = "<interactive>",
+		   args = [],
+		   targets = paths,
+		   cmstate = cmstate,
+		   options = [] }
+
+#if HAVE_READLINE_HEADERS && HAVE_READLINE_LIBS
+   Readline.resetTerminal Nothing
+#endif
+
    return ()
 
 
-runGHCi :: GHCi ()
-runGHCi = do
-  -- Read in ./.ghci.
-  let file = "./.ghci"
-  exists <- io (doesFileExist file)
-  when exists $ do
-     dir_ok  <- io (checkPerms ".")
-     file_ok <- io (checkPerms file)
-     when (dir_ok && file_ok) $ do
-   	either_hdl <- io (IO.try (openFile "./.ghci" ReadMode))
-   	case either_hdl of
-   	   Left e    -> return ()
-   	   Right hdl -> fileLoop hdl False
-  
-  -- Read in $HOME/.ghci
-  either_dir <- io (IO.try (getEnv "HOME"))
-  case either_dir of
-     Left e -> return ()
-     Right dir -> do
-	cwd <- io (getCurrentDirectory)
-    	when (dir /= cwd) $ do
-	   let file = dir ++ "/.ghci"
-	   ok <- io (checkPerms file)
-       	   either_hdl <- io (IO.try (openFile file ReadMode))
-	   case either_hdl of
-		Left e    -> return ()
-		Right hdl -> fileLoop hdl False
+runGHCi :: [FilePath] -> GHCi ()
+runGHCi paths = do
+  read_dot_files <- io (readIORef v_Read_DotGHCi)
+
+  when (read_dot_files) $ do
+    -- Read in ./.ghci.
+    let file = "./.ghci"
+    exists <- io (doesFileExist file)
+    when exists $ do
+       dir_ok  <- io (checkPerms ".")
+       file_ok <- io (checkPerms file)
+       when (dir_ok && file_ok) $ do
+  	  either_hdl <- io (IO.try (openFile "./.ghci" ReadMode))
+  	  case either_hdl of
+  	     Left e    -> return ()
+  	     Right hdl -> fileLoop hdl False
+    
+  when (read_dot_files) $ do
+    -- Read in $HOME/.ghci
+    either_dir <- io (IO.try (getEnv "HOME"))
+    case either_dir of
+       Left e -> return ()
+       Right dir -> do
+  	  cwd <- io (getCurrentDirectory)
+  	  when (dir /= cwd) $ do
+  	     let file = dir ++ "/.ghci"
+  	     ok <- io (checkPerms file)
+  	     when ok $ do
+  	       either_hdl <- io (IO.try (openFile file ReadMode))
+  	       case either_hdl of
+  		  Left e    -> return ()
+  		  Right hdl -> fileLoop hdl False
+
+  -- perform a :load for files given on the GHCi command line
+  when (not (null paths)) $
+     ghciHandle showException $
+	loadModule (unwords paths)
+
+  -- enter the interactive loop
+  interactiveLoop
+
+  -- and finally, exit
+  io $ do putStrLn "Leaving GHCi."
+
+
+interactiveLoop = do
+  -- ignore ^C exceptions caught here
+  ghciHandleDyn (\e -> case e of Interrupted -> ghciUnblock interactiveLoop
+			         _other      -> return ()) $ do
 
   -- read commands from stdin
 #if HAVE_READLINE_HEADERS && HAVE_READLINE_LIBS
@@ -186,19 +233,15 @@ runGHCi = do
   fileLoop stdin True
 #endif
 
-  -- and finally, exit
-  io $ do putStrLn "Leaving GHCi." 
-
 
 -- NOTE: We only read .ghci files if they are owned by the current user,
 -- and aren't world writable.  Otherwise, we could be accidentally 
 -- running code planted by a malicious third party.
 
--- Furthermore, We only read ./.ghci if both . and ./.ghci are
--- owned by the current user and aren't writable by anyone else.  I
--- think this is sufficient: we don't need to check .. and
--- ../.. etc. because "."  always refers to the same directory while a
--- process is running.
+-- Furthermore, We only read ./.ghci if . is owned by the current user
+-- and isn't writable by anyone else.  I think this is sufficient: we
+-- don't need to check .. and ../.. etc. because "."  always refers to
+-- the same directory while a process is running.
 
 checkPerms :: String -> IO Bool
 checkPerms name =
@@ -251,6 +294,7 @@ readlineLoop :: GHCi ()
 readlineLoop = do
    st <- getGHCiState
    mod <- io (cmGetContext (cmstate st))
+   io yield
    l <- io (readline (mod ++ "> "))
    case l of
 	Nothing -> return ()
@@ -267,50 +311,48 @@ readlineLoop = do
 -- and carries on.
 runCommand :: String -> GHCi Bool
 runCommand c = 
-  ghciHandle ( \exception -> 
-	(case exception of
-	   DynException dyn -> 
-	      case fromDynamic dyn of
-		Nothing -> io (putStrLn ("*** Exception: (unknown)"))
-		Just ghc_ex -> 
-		  case ghc_ex of
-		    PhaseFailed phase code ->
-			io ( putStrLn ("Phase " ++ phase ++ " failed (code "
-				        ++ show code ++ ")"))
-		    Interrupted -> io (putStrLn "Interrupted.")
-			-- omit the location for CmdLineError
-		    CmdLineError s -> io (putStrLn s)
-		    other -> io (putStrLn (show (ghc_ex :: GhcException)))
-
-	   other -> io (putStrLn ("*** Exception: " ++ show exception))
-
-	) >> return False
-     ) $
-
-   doCommand c
+  ghciHandle ( \exception -> do
+		flushEverything
+		showException exception
+		return False
+	     ) $
+  doCommand c
+
+showException (DynException dyn) =
+  case fromDynamic dyn of
+    Nothing               -> io (putStrLn ("*** Exception: (unknown)"))
+    Just Interrupted      -> io (putStrLn "Interrupted.")
+    Just (CmdLineError s) -> io (putStrLn s)	 -- omit the location for CmdLineError
+    Just ph@PhaseFailed{} -> io (putStrLn (showGhcException ph "")) -- ditto
+    Just other_ghc_ex     -> io (print other_ghc_ex)
+
+showException other_exception
+  = io (putStrLn ("*** Exception: " ++ show other_exception))
 
 doCommand (':' : command) = specialCommand command
 doCommand stmt
-   = do timeIt (do stuff <- runStmt stmt; finishEvalExpr stuff)
+   = do timeIt (do nms <- runStmt stmt; finishEvalExpr nms)
         return False
 
--- Returns True if the expr was successfully parsed, renamed and
--- typechecked.
-runStmt :: String -> GHCi (Maybe [Name])
+runStmt :: String -> GHCi [Name]
 runStmt stmt
- | null (filter (not.isSpace) stmt)
- = return Nothing
+ | null (filter (not.isSpace) stmt) = return []
  | otherwise
  = do st <- getGHCiState
       dflags <- io getDynFlags
       let dflags' = dopt_unset dflags Opt_WarnUnusedBinds
-      (new_cmstate, names) <- io (cmRunStmt (cmstate st) dflags' stmt)
+      (new_cmstate, result) <- 
+	io $ withProgName (progname st) $ withArgs (args st) $
+	cmRunStmt (cmstate st) dflags' stmt
       setGHCiState st{cmstate = new_cmstate}
-      return (Just names)
+      case result of
+	CmRunFailed      -> return []
+	CmRunException e -> showException e >> return []
+	CmRunDeadlocked  -> io (putStrLn "Deadlocked.") >> return []
+	CmRunOk names    -> return names
 
 -- possibly print the type and revert CAFs after evaluating an expression
-finishEvalExpr Nothing = return False
-finishEvalExpr (Just names)
+finishEvalExpr names
  = do b <- isOptionSet ShowType
       st <- getGHCiState
       when b (mapM_ (showTypeOfName (cmstate st)) names)
@@ -329,10 +371,8 @@ showTypeOfName cmstate n
 
 flushEverything :: GHCi ()
 flushEverything
-   = io $ do flush_so <- readIORef flush_stdout
-     	     flush_so
-     	     flush_se <- readIORef flush_stdout
-     	     flush_se
+   = io $ do Monad.join (readIORef flush_stdout)
+     	     Monad.join (readIORef flush_stderr)
              return ()
 
 specialCommand :: String -> GHCi Bool
@@ -357,8 +397,75 @@ noArgs c = throwDyn (CmdLineError ("command `" ++ c ++ "' takes no arguments"))
 help :: String -> GHCi ()
 help _ = io (putStr helpText)
 
+info :: String -> GHCi ()
+info "" = throwDyn (CmdLineError "syntax: `:i <thing-you-want-info-about>'")
+info s = do
+  let names = words s
+  state <- getGHCiState
+  dflags <- io getDynFlags
+  let 
+    infoThings cms [] = return cms
+    infoThings cms (name:names) = do
+      (cms, unqual, stuff) <- io (cmInfoThing cms dflags name)
+      io (putStrLn (showSDocForUser unqual (
+	    vcat (intersperse (text "") (map showThing stuff))))
+         )
+      infoThings cms names
+
+    showThing (ty_thing, fixity) 
+	= vcat [ text "-- " <> showTyThing ty_thing, 
+		 showFixity fixity (getName ty_thing),
+	         ppr (ifaceTyThing ty_thing) ]
+
+    showFixity fix name
+	| fix == defaultFixity = empty
+	| otherwise            = ppr fix <+> 
+				 (if isSymOcc (nameOccName name)
+					then ppr name
+					else char '`' <> ppr name <> char '`')
+
+    showTyThing (AClass cl)
+       = hcat [ppr cl, text " is a class", showSrcLoc (className cl)]
+    showTyThing (ATyCon ty)
+       | isPrimTyCon ty
+       = hcat [ppr ty, text " is a primitive type constructor"]
+       | otherwise
+       = hcat [ppr ty, text " is a type constructor", showSrcLoc (tyConName ty)]
+    showTyThing (AnId   id)
+       = hcat [ppr id, text " is a ", idDescr id, showSrcLoc (idName id)]
+
+    idDescr id
+       | isRecordSelector id = 
+		case tyConClass_maybe (fieldLabelTyCon (
+				recordSelectorFieldLabel id)) of
+			Nothing -> text "record selector"
+			Just c  -> text "method in class " <> ppr c
+       | isDataConWrapId id  = text "data constructor"
+       | otherwise           = text "variable"
+
+	-- also print out the source location for home things
+    showSrcLoc name
+	| isHomePackageName name && isGoodSrcLoc loc
+	= hsep [ text ", defined at", ppr loc ]
+	| otherwise
+	= empty
+	where loc = nameSrcLoc name
+
+  cms <- infoThings (cmstate state) names
+  setGHCiState state{ cmstate = cms }
+  return ()
+
+
 addModule :: String -> GHCi ()
-addModule _ = throwDyn (InstallationError ":add not implemented")
+addModule str = do
+  let files = words str
+  state <- getGHCiState
+  dflags <- io (getDynFlags)
+  io (revertCAFs)			-- always revert CAFs on load/add.
+  let new_targets = files ++ targets state 
+  (cmstate1, ok, mods) <- io (cmLoadModule (cmstate state) new_targets)
+  setGHCiState state{ cmstate = cmstate1, targets = new_targets }
+  modulesLoadedMsg ok mods
 
 setContext :: String -> GHCi ()
 setContext ""
@@ -423,26 +530,27 @@ undefineMacro macro_name = do
   io (writeIORef commands (filter ((/= macro_name) . fst) cmds))
 
 loadModule :: String -> GHCi ()
-loadModule path = timeIt (loadModule' path)
+loadModule str = timeIt (loadModule' str)
 
-loadModule' path = do
+loadModule' str = do
+  let files = words str
   state <- getGHCiState
   dflags <- io getDynFlags
   cmstate1 <- io (cmUnload (cmstate state) dflags)
-  setGHCiState state{ cmstate = cmstate1, target = Nothing }
+  setGHCiState state{ cmstate = cmstate1, targets = [] }
   io (revertCAFs)			-- always revert CAFs on load.
-  (cmstate2, ok, mods) <- io (cmLoadModule cmstate1 path)
-  setGHCiState state{ cmstate = cmstate2, target = Just path }
+  (cmstate2, ok, mods) <- io (cmLoadModule cmstate1 files)
+  setGHCiState state{ cmstate = cmstate2, targets = files }
   modulesLoadedMsg ok mods
 
 reloadModule :: String -> GHCi ()
 reloadModule "" = do
   state <- getGHCiState
-  case target state of
-   Nothing -> io (putStr "no current target\n")
-   Just path
+  case targets state of
+   [] -> io (putStr "no current target\n")
+   paths
       -> do io (revertCAFs)		-- always revert CAFs on reload.
-	    (new_cmstate, ok, mods) <- io (cmLoadModule (cmstate state) path)
+	    (new_cmstate, ok, mods) <- io (cmLoadModule (cmstate state) paths)
             setGHCiState state{ cmstate=new_cmstate }
 	    modulesLoadedMsg ok mods
 
@@ -487,8 +595,8 @@ shellEscape str = io (system str >> return False)
 -- This is pretty fragile: most options won't work as expected.  ToDo:
 -- figure out which ones & disallow them.
 
-setOptions :: String -> GHCi ()
-setOptions ""
+setCmd :: String -> GHCi ()
+setCmd ""
   = do st <- getGHCiState
        let opts = options st
        io $ putStrLn (showSDoc (
@@ -497,9 +605,25 @@ setOptions ""
    		   then text "none."
    		   else hsep (map (\o -> char '+' <> text (optToStr o)) opts)
    	   ))
-setOptions str
-  = do -- first, deal with the GHCi opts (+s, +t, etc.)
-      let (plus_opts, minus_opts)  = partition isPlus (words str)
+setCmd str
+  = case words str of
+	("args":args) -> setArgs args
+	("prog":prog) -> setProg prog
+	wds -> setOptions wds
+
+setArgs args = do
+  st <- getGHCiState
+  setGHCiState st{ args = args }
+
+setProg [prog] = do
+  st <- getGHCiState
+  setGHCiState st{ progname = prog }
+setProg _ = do
+  io (hPutStrLn stderr "syntax: :set prog <progname>")
+
+setOptions wds =
+   do -- first, deal with the GHCi opts (+s, +t, etc.)
+      let (plus_opts, minus_opts)  = partition isPlus wds
       mapM setOpt plus_opts
 
       -- now, the GHC flags
@@ -572,21 +696,23 @@ newPackages new_pkgs = do
   state <- getGHCiState
   dflags <- io getDynFlags
   cmstate1 <- io (cmUnload (cmstate state) dflags)
-  setGHCiState state{ cmstate = cmstate1, target = Nothing }
+  setGHCiState state{ cmstate = cmstate1, targets = [] }
 
   io $ do
     pkgs <- getPackageInfo
     flushPackageCache pkgs
    
     new_pkg_info <- getPackageDetails new_pkgs
-    mapM_ (linkPackage False) (reverse new_pkg_info)
+    mapM_ linkPackage (reverse new_pkg_info)
 
 -----------------------------------------------------------------------------
 -- GHCi monad
 
 data GHCiState = GHCiState
      { 
-	target         :: Maybe FilePath,
+	progname       :: String,
+	args	       :: [String],
+	targets        :: [FilePath],
 	cmstate        :: CmState,
 	options        :: [GHCiOption]
      }
@@ -609,6 +735,10 @@ instance Monad GHCi where
   (GHCi m) >>= k  =  GHCi $ \s -> m s >>= \a -> unGHCi (k a) s
   return a  = GHCi $ \s -> return a
 
+ghciHandleDyn :: Typeable t => (t -> GHCi a) -> GHCi a -> GHCi a
+ghciHandleDyn h (GHCi m) = GHCi $ \s -> 
+   Exception.catchDyn (m s) (\e -> unGHCi (h e) s)
+
 getGHCiState   = GHCi $ \r -> readIORef r
 setGHCiState s = GHCi $ \r -> writeIORef r s
 
@@ -627,7 +757,8 @@ unsetOption opt
  = do st <- getGHCiState
       setGHCiState (st{ options = filter (/= opt) (options st) })
 
-io m = GHCi $ \s -> m >>= \a -> return a
+io :: IO a -> GHCi a
+io m = GHCi { unGHCi = \s -> m >>= return }
 
 -----------------------------------------------------------------------------
 -- recursive exception handlers
@@ -665,32 +796,40 @@ showLS (Right nm) = "(dynamic) " ++ nm
 
 linkPackages :: [LibrarySpec] -> [PackageConfig] -> IO ()
 linkPackages cmdline_lib_specs pkgs
-   = do sequence_ [ linkPackage (name p `elem` loaded) p | p <- reverse pkgs ]
+   = do mapM_ linkPackage (reverse pkgs)
         lib_paths <- readIORef v_Library_paths
         mapM_ (preloadLib lib_paths) cmdline_lib_specs
+	if (null cmdline_lib_specs)
+	   then return ()
+	   else do putStr "final link ... "
+		   ok <- resolveObjs
+		   if ok then putStrLn "done."
+	      		 else throwDyn (InstallationError 
+                                          "linking extra libraries/objects failed")
      where
-	-- packages that are already linked into GHCi
-	loaded = [ "concurrent", "posix", "text", "util" ]
-
         preloadLib :: [String] -> LibrarySpec -> IO ()
         preloadLib lib_paths lib_spec
            = do putStr ("Loading object " ++ showLS lib_spec ++ " ... ")
                 case lib_spec of
                    Left static_ish
                       -> do b <- preload_static lib_paths static_ish
-                            putStrLn (if b then "done" else "not found")
+                            putStrLn (if b then "done." else "not found")
                    Right dll_unadorned
                       -> -- We add "" to the set of paths to try, so that
                          -- if none of the real paths match, we force addDLL
                          -- to look in the default dynamic-link search paths.
-                         do b <- preload_dynamic (lib_paths++[""]) dll_unadorned
-                            when (not b) (cantFind lib_paths lib_spec)
+                         do maybe_errstr <- preload_dynamic (lib_paths++[""]) 
+                                                            dll_unadorned
+                            case maybe_errstr of
+                               Nothing -> return ()
+                               Just mm -> preloadFailed mm lib_paths lib_spec
                             putStrLn "done"
 
-        cantFind :: [String] -> LibrarySpec -> IO ()
-        cantFind paths spec
-           = do putStr ("failed.\nCan't find " ++ showLS spec
-                        ++ " in directories:\n"
+        preloadFailed :: String -> [String] -> LibrarySpec -> IO ()
+        preloadFailed sys_errmsg paths spec
+           = do putStr ("failed.\nDynamic linker error message was:\n   " 
+                        ++ sys_errmsg  ++ "\nWhilst trying to load:  " 
+                        ++ showLS spec ++ "\nDirectories to search are:\n"
                         ++ unlines (map ("   "++) paths) )
                 give_up
 
@@ -700,26 +839,40 @@ linkPackages cmdline_lib_specs pkgs
                 if not b then return False
                          else loadObj name >> return True
 
+        -- return Nothing == success, else Just error message from addDLL
         preload_dynamic [] name
-           = return False
+           = return Nothing
         preload_dynamic (path:paths) rootname
-           = do maybe_errmsg <- addDLL path rootname
-                if    maybe_errmsg /= nullPtr
+           = do -- addDLL returns NULL on success
+                maybe_errmsg <- addDLL path rootname
+                if    maybe_errmsg == nullPtr
                  then preload_dynamic paths rootname
-                 else return True
+                 else do str <- peekCString maybe_errmsg
+                         return (Just str)
 
         give_up 
            = (throwDyn . CmdLineError)
                 "user specified .o/.so/.DLL could not be loaded."
 
-
-linkPackage :: Bool -> PackageConfig -> IO ()
--- ignore rts and gmp for now (ToDo; better?)
-linkPackage loaded_in_ghci pkg
-   | name pkg `elem` ["rts", "gmp"] 
-   = return ()
+-- Packages that don't need loading, because the compiler shares them with
+-- the interpreted program.
+dont_load_these = [ "gmp", "rts" ]
+
+-- Packages that are already linked into GHCi.  For mingw32, we only
+-- skip gmp and rts, since std and after need to load the msvcrt.dll
+-- library which std depends on.
+loaded_in_ghci
+#          ifndef mingw32_TARGET_OS
+           = [ "std", "concurrent", "posix", "text", "util" ]
+#          else
+	   = [ ]
+#          endif
+
+linkPackage :: PackageConfig -> IO ()
+linkPackage pkg
+   | name pkg `elem` dont_load_these = return ()
    | otherwise
-   = do putStr ("Loading package " ++ name pkg ++ " ... ")
+   = do 
         -- For each obj, try obj.o and if that fails, obj.so.
         -- Complication: all the .so's must be loaded before any of the .o's.  
         let dirs      =  library_dirs pkg
@@ -729,13 +882,15 @@ linkPackage loaded_in_ghci pkg
 	-- Don't load the .so libs if this is a package GHCi is already
 	-- linked against, because we'll already have the .so linked in.
 	let (so_libs, obj_libs) = partition isRight classifieds
-        let sos_first | loaded_in_ghci = obj_libs
-		      | otherwise      = so_libs ++ obj_libs
+        let sos_first | name pkg `elem` loaded_in_ghci = obj_libs
+		      | otherwise      		       = so_libs ++ obj_libs
 
+	putStr ("Loading package " ++ name pkg ++ " ... ")
         mapM loadClassified sos_first
         putStr "linking ... "
-        resolveObjs
-        putStrLn "done."
+        ok <- resolveObjs
+	if ok then putStrLn "done."
+	      else panic ("can't load package `" ++ name pkg ++ "'")
      where
         isRight (Right _) = True
         isRight (Left _)  = False
@@ -748,7 +903,7 @@ loadClassified (Right dll_unadorned)
         if    maybe_errmsg == nullPtr
          then return ()
          else do str <- peekCString maybe_errmsg
-                 throwDyn (CmdLineError ("can't find .o or .so/.DLL for: " 
+                 throwDyn (CmdLineError ("can't load .so/.DLL for: " 
                                        ++ dll_unadorned ++ " (" ++ str ++ ")" ))
 
 locateOneObj :: [FilePath] -> String -> IO LibrarySpec