Hello,
On Thu, Oct 16, 2014 at 3:58 AM, Adam Gundry
One problem I've run into is transforming the flattened CFunEqCans into unflattened form (so the flatten-skolems don't get in the way of AG-unification). Do you know if there is an easy way to do this, or do I need to rebuild the tree manually in the plugin?
One thing that occurred to me about this: when constraints are "flattened", it is easy for a plugin to pick-out only the one that it cares about. If things were fully unflattened, this would not be the case... For example, if I have a constraint: (2 + F a) ~ F a + F a In the flattened form, this will become: (F a ~ f1, 2 + f1 ~ f2, f1 + f2 ~ f3, f2 ~ f3) So, the type-nats plugin would pick out: (2 + f1 ~ f2, f1 + f2 ~ f3, f2 ~ f3), and ignore (F a ~ f1), as it knows nothing about arbitrary type functions. So, if we want to do un-flattening, I think we should do it only on those constraints that are of interest to the plugin.
Also, I notice that you are providing only equality constraints to the plugin. Is there any reason we can't make other types of constraint available as well? For example, one might want to introduce a typeclass with a special solution strategy (cf. Coercible, or the Has class in OverloadedRecordFields).
Yeah, we should probably pass-in all constraints, inlcluding derived ones. The reason it is not like that is pretty much historical now. So I'll have a go at making this change. -Iavor
- As an example, I've extracted my work on using an SMT solver at the type level as a separate plugin:
https://github.com/yav/type-nat-solver
- To see how to invoke a module that uses a plugin, have a look in `examples/A.hs`. (Currently, the plugin assumes that you have `cvc4` installed and available in the path).
- Besides this, we don't have much documentation yet. For hackers: we tried to use `tcPlugin` on `TcPlugin` in the names of all things plugin related, so you could grep for this. The basic API types and functions are defined in `TcRnTypes` and `TcRnMonad`.
Happy hacking, -Iavor
-- Adam Gundry, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/