Proposed changes to typechecker plugins API

[Adam Gundry]

Hi devs,

I thought I should flag up some proposed changes relating to typechecker
plugins, which Christiaan, Iavor and I have been discussing. The quick
summary:

 * make it possible for plugins to create constraints (Phab:D909);

 * make it easier for plugins to define special type families;

 * embed CoreExpr in EvTerm.

For more details, see the wiki page:
https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker#Post-7.10changestoTcPluginMAPI

Questions/review/comments very welcome.

Adam


-- 
Adam Gundry, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com/