Hi Adam, I've added a README which tries to explain things: https://github.com/aavogt/HListPlugin
When I produce a wanted constraint from a wanted constraint, things work as I wanted. Thanks for the suggestion! Regards, Adam On Mon, Feb 16, 2015 at 4:36 AM, Adam Gundry <a...@well-typed.com> wrote: > Hi Adam, > > It's great to hear that you are trying the plugins functionality, this > is exactly the kind of experimentation it's designed for! I'm a little > confused about what you're trying to achieve, though. Can you give some > examples of code you'd like to be able to write? > > In general, GHC's type inference algorithm isn't expecting wanted > constraints to be produced from givens; confusing things will happen if > they are, and it's likely that *less* things will be typeable rather > than *more*. Perhaps the plugin infrastructure should prevent you from > doing so. > > It makes sense to produce givens from givens or wanteds from wanteds > though. I'd imagine you might want to look for *wanted* constraints > (HLength x ~ HLength y) and add an additional *wanted* (SameLength x y). > > One other thing to note is that plugins are called twice, once to > simplify the givens (with empty wanteds), and once to solve the wanteds > (https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker#Callingpluginsfromthetypechecker). > > Hope this helps, _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
