[GHC] #10431: EqualityConstraints extension?

[GHC]

#10431: EqualityConstraints extension?
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              Reporter:  adamgundry  |             Owner:
                  Type:  feature     |            Status:  new
  request                            |         Milestone:  7.12.1
              Priority:  normal      |           Version:  7.11
             Component:  Compiler    |  Operating System:  Unknown/Multiple
  (Type checker)                     |   Type of failure:  None/Unknown
              Keywords:              |        Blocked By:
          Architecture:              |   Related Tickets:
  Unknown/Multiple                   |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 At the moment, writing an equality constraint in a type requires at least
 one of the `GADTs` or `TypeFamilies` extensions. However, each of these
 has other effects. Could we have an `EqualityConstraints` extension to
 permit equality constraints in types, but neither GADTs nor type families?
 Presumably this extension should imply `MonoLocalBinds`.

 The `GADTs` extension could then become precisely the conjunction of
 `GADTSyntax`, `EqualityConstraints` and `ExistentialQuantification`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10431>
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