[GHC] #10056: Inconsistent precedence of ~

[GHC]

#10056: Inconsistent precedence of ~
-------------------------------------+-------------------------------------
        Reporter:  crockeea          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       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, #10431,   |  Differential Rev(s):  Phab:D4876
  #14316                             |
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 Ah!  I'd forgotten about `-XStrict`. So the special treatment in
 `Parsery.y` is (only) here
 {{{
 strictness :: { Located ([AddAnn], SrcStrictness) }
         : '!' { sL1 $1 ([mj AnnBang $1], SrcStrict) }
         | '~' { sL1 $1 ([mj AnnTilde $1], SrcLazy) }
 }}}
 So is `(~)` (in types) handled uniformly with `(!)`?  It seems not.
 Perhaps that's because we don't want to give up `(~)` as an infix
 operator, but we are willing to give up `(!)`?

 I got as far as reading `splitTilde` but got lost in its invocations in
 `RdrHsSyn` and `Parser.y`.

 Anyway, it'd be good to summarise how the moving parts fit together, in a
 Note.  There are some e.g. `Note [Parsing ~]`, but they are too brief to
 do justice to the question.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10056#comment:41>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler