Hi Adam, Hi Eric, At least for what I want to use them for [1] it would be nice if there was an easy way to say: If you are stuck on solving "Constraint a b TypeC", then you should pick, e.g.: - "a ~ TypeA" and "b ~ TypeB" (What I am actually trying to say is: use the instance "Constraint TypeA TypeB TypeC") - "a ~ b" Currently I am producing equality constraints, like this: mkDerivedTypeEqCt :: TcTyVar -> TcType -> TcPluginM Ct mkDerivedTypeEqCt tyVar ty = do (_, lclEnv) <- getEnvs return $ CTyEqCan { cc_ev = CtDerived -- :: CtEvidence { ctev_pred = ty -- :: TcPredType -- This matches type-wise, but I have no idea what actually belongs here. , ctev_loc = mkGivenLoc topTcLevel (UnifyForAllSkol [tyVar] ty) lclEnv -- :: CtLoc -- Again no idea what actually belongs here: -- topTcLevel :: TcLevel -- To what does this relate? I guess top level -- is ok for equality constraints -- (UnifyForAllSkol [tyVar] ty) :: SkolemInfo -- This one matches what we have at disposal (no idea if it is the right one). -- lclEnv :: TcLclEnv -- I just use the only one I know. } , cc_tyvar = tyVar -- :: TcTyVar , cc_rhs = ty -- :: TcType , cc_eq_rel = NomEq -- :: EqRel -- Alternative would be ReprEq. Whats the difference? } Which seems to be working, but still leaves a lot of open questions (see comments). Maybe my problems using the API are more related to missing documentation, then lack of API functionality. Jan [1]: https://mail.haskell.org/pipermail/ghc-devs/2015-February/008414.html On Wed, 27 May 2015 07:13:37, Eric Seidel wrote:
Hi Adam,
I like the addition of the new* functions for creating constraints, that should make for a much nicer API than dealing directly with the CtEvidence constructors!
I'm not so convinced however about embedding arbitrary CoreExprs in EvTerms. First of all, it feels a bit strange to generate CoreExprs before the desugarer (and we would have to add a `MonadThings TcPluginM` instance to generate Integer and String CoreExprs).
But more importantly, based on your wiki page [1], it sounds like what we really want is a nice API for creating dictionaries.
Eric
[1]:
https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker#EmbeddingCoreExpri...
On Wed, May 27, 2015, at 01:33, Adam Gundry wrote:
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-7.10changesto...
Questions/review/comments very welcome.
Adam
-- Adam Gundry, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/ _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs