[Template-haskell] Some ideas

[Simon Peyton-Jones]

| Using this we could say (on the toplevel of a module):
| addDeriving ("Fold", deriveFold)
| 
| Note that this would let us derive not only instances but new
| functions or even new data types. Mega Awsome!

Can't you do this already?

	data T = MkT Int

	$(deriveFold 'T)

where deriveFold :: TH.Name -> Q [Dec]

| Splicing pragmas
| ===============
| 
| It would be nice to be able to splice in compiler pragmas. For example
| if one writes a TH module for deriving folds and builds one would like
| to generate rules pragmas so that GHC can fuse these functions when
| they are used. Generating self-optimising code :).
| 
| Concretely one would add a constructor to the Dec data type. Something
| like this:
| 
| data Dec = ...
|      | PragmaD Pragma

Yes, more and more GHC extensions are creeping into TH, and maybe that's
OK.  It is tiresome, but not difficult, to extend the abstract syntax
and to-and-fro conversions.  Ian Lynagh has become quite good at it.  OK
with me!


| >From Meta Haskell to Meta X
| ===========================

I don't know how to make a good job of this, but it seems like a good
problem for someone to study.  The thing is that language X has scoping
and typing rules that are different to Haskell's.  How to express them?
It's not just syntax!

Simon