#14961: QuantifiedConstraints: introducing classes through equality constraints fails -------------------------------------+------------------------------------- Reporter: mrkgnao | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 Resolution: | Keywords: | QuantifiedConstraints wipT2893 Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #14860 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mrkgnao): I think it would be good to add it as a regression test. Optics seem like an area where `QuantifiedConstraints` could simplify many things a lot! Also, is the incompatibility of `QuantifiedConstraints`-using bindings with `:type` in GHCi, or the inability to write, e.g. {{{#!hs _Left1 :: c ~=> Choice => Glass c '(Either a x, Either b x) '(a, b) _Left1 = Glass left' _Left4 = _Left1 {- src/Main.hs:73:10: error: • Could not deduce (Choice x1) arising from a use of ‘_Left1’ from the context: c x1 bound by a quantified context at src/Main.hs:73:1-15 Possible fix: add (Choice x1) to the context of a quantified context • In the expression: _Left1 In an equation for ‘_Left4’: _Left4 = _Left1 -} }}} expected? (I have `-XNoMonomorphismRestriction` on if that's relevant.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14961#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler