#11715: Constraint vs * -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.0.1-rc1 checker) | Resolution: | Keywords: Typeable Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by int-index): I find pretending that `Int` is a constraint to be quite appealing, actually: it elevates the intuition that `=>` is like `->`, only implicit. The current design of `ImplicitParameters` will be easily expressible on top of this new feature with `(?param :: T) => t` desugaring into `Tagged "param" T =>` at type level and `?cmp` desugaring into `unTagged @"param" reflect` at term level. To sum it up, making `Type ~ Constraint` unifies/simplifies: * The `Dict` wrapper * `Typeable` & type-indexed `TypeRep` * `Given`-style and `Reifies`-style reflection * `-XImplicitParameters` To me, this kind of simplification is far from "distasteful". Meanwhile, I agree with issue (1) from comment:31 and we should certainly document to what problems `incoherentWith` leads, and actively discourage its incorrect use. I wouldn't be happy if people started using it to model implicits from Scala (which are basically incoherent type classes). It's still a useful function to have, though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11715#comment:37 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler