fix #1200: don't evaluate the result of main

diff --git a/utils/runghc/runghc.hs b/utils/runghc/runghc.hs
index 83163bd..cdf06dc 100644 (file)
--- a/utils/runghc/runghc.hs
+++ b/utils/runghc/runghc.hs
@@ -58,13 +58,17 @@ doIt ghc args = do
                        "-ignore-dot-ghci" : ghc_args ++ 
                        [ "-e","System.Environment.withProgName "++show filename++" (System.Environment.withArgs ["
                          ++ concat (intersperse "," (map show prog_args))
                        "-ignore-dot-ghci" : ghc_args ++ 
                        [ "-e","System.Environment.withProgName "++show filename++" (System.Environment.withArgs ["
                          ++ concat (intersperse "," (map show prog_args))

-                         ++ "] (GHC.TopHandler.runIOFastExit Main.main))", filename])
+                         ++ "] (GHC.TopHandler.runIOFastExit (Main.main Prelude.>> (Prelude.return ()))))", filename])

                -- runIOFastExit: makes exceptions raised by Main.main
                -- behave in the same way as for a compiled program.
                -- 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.
                -- runIOFastExit: makes exceptions raised by Main.main
                -- behave in the same way as for a compiled program.
                -- 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.

+               --
+               -- Why (main >> return ()) rather than just main?  Because
+               -- otherwise GHCi by default tries to evaluate the result
+               -- of the IO in order to show it (see #1200).

          exitWith res
 
 notArg ('-':_) = False
          exitWith res
 
 notArg ('-':_) = False