GHCi 6.4.2 reports an internal error: unknown/strange object

I have a medium-sized interpreted program that seems to corrupt the heap when running under GHCi. Here's a couple of examples. (Ignore the first run, of course.)

C:\Documents and Settings\johndetr\My Documents\Haskell\Eval>ghci
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.4.2, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base-1.0 ... linking ... done.
Prelude> :load Main
Compiling Types            ( ./Types.hs, interpreted )
Compiling Layout           ( ./Layout.hs, interpreted )
Compiling Eval             ( ./Eval.hs, interpreted )
Compiling Main             ( Main.hs, interpreted )
Ok, modules loaded: Main, Eval, Layout, Types.
*Main> main
Loading package haskell98-1.0 ... linking ... done.
Loading package haskell-src-1.0 ... linking ... done.
HsVar (UnQual (HsIdent "result"))
338350
[Node (Color 0.0 0.5 0.0) 12005 "338350"]
GHC's heap exhausted: current limit is 268435456 bytes;
Use the `-M<size>' option to increase the total heap size.

C:\Documents and Settings\johndetr\My Documents\Haskell\Eval>ghci +RTS -M500m
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.4.2, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base-1.0 ... linking ... done.
Prelude> :load Main
Compiling Types            ( ./Types.hs, interpreted )
Compiling Layout           ( ./Layout.hs, interpreted )
Compiling Eval             ( ./Eval.hs, interpreted )
Compiling Main             ( Main.hs, interpreted )
Ok, modules loaded: Main, Eval, Layout, Types.
*Main> main
Loading package haskell98-1.0 ... linking ... done.
Loading package haskell-src-1.0 ... linking ... done.
HsVar (UnQual (HsIdent "result"))
338350
[Node (Color 0.0 0.5 0.0) 12005 "338350"]
<interactive>: internal error: update_fwd: unknown/strange object  38769
    Please report this as a compiler bug.  See:
    http://www.haskell.org/ghc/reportabug

C:\Documents and Settings\johndetr\My Documents\Haskell\Eval>ghci +RTS -M800m
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.4.2, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base-1.0 ... linking ... done.
Prelude> :load Main
Compiling Types            ( ./Types.hs, interpreted )
Compiling Layout           ( ./Layout.hs, interpreted )
Compiling Eval             ( ./Eval.hs, interpreted )
Compiling Main             ( Main.hs, interpreted )
Ok, modules loaded: Main, Eval, Layout, Types.
*Main> main

<interactive>:1:0: Not in scope: `gain'
*Main> main
Loading package haskell98-1.0 ... linking ... done.
Loading package haskell-src-1.0 ... linking ... done.
HsVar (UnQual (HsIdent "result"))
338350
[Node (Color 0.0 0.5 0.0) 12005 "338350"]
<interactive>: internal error: update_fwd: unknown/strange object  38769
    Please report this as a compiler bug.  See:
    http://www.haskell.org/ghc/reportabug

So, would you like the source files? Or how else can I help?

Also, I run into the "gain" bug above quite often when I type ahead to GHCi under Windows. I assume this is known behavior.

Finally, when I got the initial message above to use the -M flag, it took me forever to remember to add the +RTS flag. Perhaps the message could be reworded to help people like me?

Cheers, John

Trac metadata

Trac field	Value
Version	6.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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