[GHC] #10056: Inconsistent precedence of ~

[GHC]

#10056: Inconsistent precedence of ~
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        Reporter:  crockeea          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.4
  (Parser)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10059            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I few comments as I'm catching up on this thread:
 * We don't need to conform to any standards here. We're talking about
 type-level operators, so we're already beyond the Haskell reports.
 Thinking about standards is a Good Thing, but I just want to note that
 we're already quite off the map.

 * I think that, given the laziness annotation wrinkle, `~` will have to
 stay somewhat magical in the parser. (That may not have been true when
 this ticket started, as I think allowing laziness annotations in types
 came about only with `-XStrictData`.)

 * However, I think we ''can'' eliminate `HsEqTy` from `HsType`. Instead,
 just use `HsOpTy` with `eqTyCon_RDR` as the operator. Once we get rid of
 `HsEqTy`, I think we'll be well on our way to solving this ticket. Indeed,
 that's probably a good approach: get rid of `HsEqTy` and get everything to
 work again.

 * Parsing `->` is magical. And it has to be: we can write `forall a. a ->
 forall b. b -> (a,b)`, for example. `forall` can't appear to the right of
 other operators. And `->` has various other special things about it (like
 being able to appear in record GADT syntax). So we have to keep this in
 mind.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10056#comment:27>
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