On Mon, Mar 17, 2014 at 2:45 PM, Simon Peyton Jones <simonpj@microsoft.com> wrote:
| The one interesting case is T4306 which fails because the generated name
| $wupd is regarded as an infix name, and thus with my new code is
| rendered as
|
|    ($wupd) :: GHC.Prim.Double# -> GHC.Prim.Double#
|
| instead of the old
|
|    $wupd :: GHC.Prim.Double# -> GHC.Prim.Double#

I think it'd also be ok just to accept this output too. These "$wxx" names are generated by GHC and won't show up in user output.  It doesn't much matter displaying them in parens.

Do they show up in -ddump-simpl? It would be nice to keep that output as readable as possible, as there are quite a few of us that read it on a regular basis.
 
But changing isLexVarSym is probably equally fine too.  I think (worth a check) that it's only called for display purposes, and not in any performance-critical parts.

Whichever you choose, add a Note with isLexVarSym to explain the issue and the choice.

Does that mean that any operator that starts with $ will now not be considered infix for printing purposes?

-- Johan