GADT Strangeness

[Simon Peyton-Jones]

| Thanks very much for this. I would never have guessed to use
| -XRelaxedPolyRec given the error message.
|
| Is it worth noting it here
| http://haskell.org/haskellwiki/Upgrading_packages#Changes_to_GADT_matching
| or is it something that has always existed with GADTs and I just didn't
| trip over it?

I've added a para.  Good idea.

| > This is a nasty corner I agree.  GHC requires -XGADTs for you to
| > *define* a GADT. Perhaps it should also require -XGADTs for you to
| > *match against* one (as you are doing here).  That would avoid this
| > particular hole.  If you think that would be a step forward, do put
| > forward a Trac feature request, and encourage others to support it.
|
| I would vote for this. In fact I was mildly surprised I could use GADTs
| without specifying -XGADTs.
|
| I noticed that Isaac Dupree has already raised a ticket
| http://permalink.gmane.org/gmane.comp.lang.haskell.glasgow.user/16109 so
| I will add my support to it.

OK.  let's see if anyone else comments.  Do ping me in a while to action it if I forget.

Simon