[GHC] #11715: Constraint vs *

[GHC]

#11715: Constraint vs *
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        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:                    |
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Comment (by int-index):

 I see no need for writing a body neither for `reify` nor `with` -- just
 make them GHC primitives.

 As to what to do when multiple constraints are in scope, I think that GHC
 should refuse to compile:

 {{{
 with (10 :: Int) $
   with (20 :: Int) $
     -- When GHC looks for an `Int` to satisfy
     -- the `Int =>` constraint, it finds both
     -- 10 and 20, so it's a compile-time error.
     (reify :: Int)
 }}}

 Am I missing something important?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11715#comment:19>
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