[Haskell-cafe] Re: A problem with par and modules boundaries...

[Duncan Coutts]

On Sun, 2009-05-24 at 12:48 -0400, Mario Blažević wrote:

> > How about diffing the whole core output (and using -ddump-simpl). If
> > there's a performance difference then there must be a difference in the
> > core code too.

> I can't exactly use diff because the generated identifier names are not the same,
> but after poring over with Emacs ediff I have found only one difference that's
> not attributable to identifiers:
> 
> $diff main.simpl imported.simpl
> ...
> 223c232
> <       a_s1rs [ALWAYS Just L] :: GHC.Integer.Internals.Integer
> ---
> >       a_s1sV [ALWAYS Just S] :: GHC.Integer.Internals.Integer
> ...

Good find!

> Does this S vs. L difference have anything to do with strictness and laziness?

Yes.

So, I think we should open a ghc but report with all the details,
particularly the example's source, the ghc version and that highlight of
that strictness difference.

Duncan