--- old-Y/ghc/compiler/main/GHC.hs	2005-10-24 22:40:44.000000000 +0200
+++ new-Y/ghc/compiler/main/GHC.hs	2005-10-24 20:23:09.000000000 +0200
@@ -346,26 +346,47 @@
 -- Flags & settings
 
 -- | Grabs the DynFlags from the Session
 getSessionDynFlags :: Session -> IO DynFlags
 getSessionDynFlags s = withSession s (return . hsc_dflags)
 
 -- | Updates the DynFlags in a Session
 setSessionDynFlags :: Session -> DynFlags -> IO ()
 setSessionDynFlags s dflags = modifySession s (\h -> h{ hsc_dflags = dflags })
 
+-- | Get the name of the top-level module (could be changed by -main-is)
+getMainMod :: DynFlags -> String
+getMainMod dflags = mainModIs dflags `orElse` "Main"
+
 -- | Messages during compilation (eg. warnings and progress messages)
 -- are reported using this callback.  By default, these messages are
 -- printed to stderr.
 setMsgHandler :: (String -> IO ()) -> IO ()
 setMsgHandler = ErrUtils.setMsgHandler
 
+-- | If there is no -o option, guess the name of target executable
+-- by using top-level source file name as a base.
+guessOutputFile :: Session -> IO ()
+guessOutputFile s = modifySession s $ \env ->
+    let dflags = hsc_dflags env
+        mod_graph = hsc_mod_graph env
+        mainModuleSrcPath, guessedName :: Maybe String
+        mainModuleSrcPath = do
+            let isMain = (== getMainMod dflags) . moduleUserString . ms_mod
+            [ms] <- return (filter isMain mod_graph)
+            ml_hs_file (ms_location ms)
+        guessedName = fmap (fst . splitFilename) mainModuleSrcPath
+    in
+    case outputFile dflags of
+        Just _ -> env
+        Nothing -> env { hsc_dflags = dflags { outputFile = guessedName } }
+
 -- -----------------------------------------------------------------------------
 -- Targets
 
 -- ToDo: think about relative vs. absolute file paths. And what
 -- happens when the current directory changes.
 
 -- | Sets the targets for this session.  Each target may be a module name
 -- or a filename.  The targets correspond to the set of root modules for
 -- the program\/library.  Unloading the current program is achieved by
 -- setting the current set of targets to be empty, followed by load.
@@ -479,20 +500,21 @@
 	-- Dependency analysis first.  Note that this fixes the module graph:
 	-- even if we don't get a fully successful upsweep, the full module
 	-- graph is still retained in the Session.  We can tell which modules
 	-- were successfully loaded by inspecting the Session's HPT.
 	mb_graph <- depanal s [] False
 	case mb_graph of
 	   Left msgs       -> do msg_act msgs; return Failed
 	   Right mod_graph -> loadMsgs2 s how_much msg_act mod_graph 
 
 loadMsgs2 s@(Session ref) how_much msg_act mod_graph = do
+        guessOutputFile s
 	hsc_env <- readIORef ref
 
         let hpt1      = hsc_HPT hsc_env
         let dflags    = hsc_dflags hsc_env
         let ghci_mode = ghcMode dflags -- this never changes
 
 	-- The "bad" boot modules are the ones for which we have
 	-- B.hs-boot in the module graph, but no B.hs
 	-- The downsweep should have ensured this does not happen
 	-- (see msDeps)
@@ -608,23 +630,22 @@
 	      cleanTempFilesExcept dflags (ppFilesFromSummaries modsDone)
 
 	      -- Issue a warning for the confusing case where the user
 	      -- said '-o foo' but we're not going to do any linking.
 	      -- We attempt linking if either (a) one of the modules is
 	      -- called Main, or (b) the user said -no-hs-main, indicating
 	      -- that main() is going to come from somewhere else.
 	      --
 	      let ofile = outputFile dflags
 	      let no_hs_main = dopt Opt_NoHsMain dflags
-	      let mb_main_mod = mainModIs dflags
 	      let 
-	 	main_mod = mb_main_mod `orElse` "Main"
+	 	main_mod = getMainMod dflags
 		a_root_is_Main 
                	    = any ((==main_mod).moduleUserString.ms_mod) 
                     	  mod_graph
 		do_linking = a_root_is_Main || no_hs_main
 
 	      when (ghci_mode == BatchCompile && isJust ofile && not do_linking) $
 	        debugTraceMsg dflags 1 ("Warning: output was redirected with -o, " ++
 				   "but no output will be generated\n" ++
 				   "because there is no " ++ main_mod ++ " module.")
 

diff -rN -u10 old-Y/ghc/docs/users_guide/separate_compilation.xml new-Y/ghc/docs/users_guide/separate_compilation.xml
--- old-Y/ghc/docs/users_guide/separate_compilation.xml	2005-10-24 22:40:44.000000000 +0200
+++ new-Y/ghc/docs/users_guide/separate_compilation.xml	2005-10-24 22:37:10.000000000 +0200
@@ -246,20 +246,37 @@
             file, the extension "<filename>.exe</filename>" is added
             if the specified filename does not already have an
             extension.  Thus
 <programlisting>
    ghc -o foo Main.hs
 </programlisting>
           will compile and link the module
           <filename>Main.hs</filename>, and put the resulting
           executable in <filename>foo.exe</filename> (not
           <filename>foo</filename>).</para>
+
+          <para>If you use <command>ghc --make</command> and you don't
+          use the <option>-o</option>, the name GHC will choose
+          for the executable will be based on the name of the file
+          containing the module <literal>Main</literal>. 
+          Note that with GHC the <literal>Main</literal> module doesn't
+          have to be put in file <filename>Main.hs</filename>.
+          Thus both
+<programlisting>
+   ghc --make Prog
+</programlisting>
+          and
+<programlisting>
+   ghc --make Prog.hs
+</programlisting>
+          will produce <filename>Prog</filename> (or
+          <filename>Prog.exe</filename> if you are on Windows).</para>
 	  </listitem>
 	</varlistentry>
 
 	<varlistentry>
 	  <term>
             <option>-odir</option> <replaceable>dir</replaceable>
             <indexterm><primary><option>-odir</option></primary></indexterm>
           </term>
 	  <listitem>
 	    <para>Redirects object files to directory