Preparing for a review of pattern synonyms

[Simon Peyton-Jones]

| > Is Haddock a part of GHC? I don't know. If it's not, then whatever
| > parser it's using will have to be extended to support pattern
| synonyms.
| 
| Haddock uses GHC's parser, but it will need to be taught about pattern
| synonyms and how to render them in documentation.

Yes, it's in utils/haddock in the main tree, and that really does need to be done before release.

| One of the things that we ought to be able to do with this extension is
| to provide abstract datatypes with pattern matching support.  The only
| thing missing is support for exhaustive pattern matches.  F# active
| patterns has it!

We already lack exhaustiveness support as soon as we have guards or view patterns.  But it seems a bit more feasible with pattern synonyms. Something to add to the "missing features" list!

Simon