Go ahead and make suggestions here. Since a CoAxiomRule embodies essentially arbitrary computation, it's hardly surprising that there's a fixed range of possibilities. I suppose that for extensibilty, any particular plugin could say "TypeNats:Rule1", "TypeNats:Rule" etc, and recognise that at the other end. We'd just need generic way to identify a plugin, plus an Int to say which axiom from that plugin. Anyway, it's all to play for. Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Adam | Gundry | Sent: 11 December 2014 12:23 | To: Iavor Diatchki; Eric Seidel | Cc: ghc-devs@haskell.org | Subject: Serialising evidence generated by typechecker plugins | | Hi folks, | | I've just discovered tcIfaceCoAxiomRule, which is used when typechecking | a coercion from an interface file. It turns out that CoAxiomRules are | represented in interface files by their names, so tcIfaceCoAxiomRule | looks up this name in a map containing all the built-in | typeNatCoAxiomRules. | | Unfortunately, this lookup fails when a plugin has defined its own | CoAxiomRule (as both uom-plugin and type-nat-solver do)! This means that | if a module uses a plugin and exports some of the evidence generated via | an unfolding, importing the module may result in a tcIfaceCoAxiomRule | panic. | | At the moment, both plugins generate fake CoAxiomRules that can prove | the equality of any types, so one workaround would be to expose this | ability in the TcCoercion type (i.e. add the equivalent of UnivCo). In | the future, however, it would be nice if plugins could actually generate | bona fide evidence based on their own axioms (e.g. the abelian group | laws, for uom-plugin). | | We can't currently serialise CoAxiomRule directly, because it contains a | function in the coaxrProves field. Could we support an alternative | first-order representation that could be serialised? This probably | wouldn't be as expressive, in particular it might not cover the built-in | axioms that define type-level comparison functions and arithmetic | operators, but it would allow plugins to axiomatize algebraic theories. | | Any thoughts? | | Adam | | P.S. I've updated https://phabricator.haskell.org/D553 with the | TcPluginM changes we discussed. | | | -- | Adam Gundry, Haskell Consultant | Well-Typed LLP, http://www.well-typed.com/ | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://www.haskell.org/mailman/listinfo/ghc-devs