[GHC] #13637: Printing type operators adds extraneous parenthesis

[GHC]

#13637: Printing type operators adds extraneous parenthesis
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        Reporter:  darchon           |                Owner:  alanz
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
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 harpocrates):

 This seems to be by design. Taken from `BasicTypes`:

 {{{
 Note [Type operator precedence]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We don't keep the fixity of type operators in the operator. So the
 pretty printer follows the following precedence order:

    TyConPrec         Type constructor application
    TyOpPrec/FunPrec  Operator application and function arrow

 We have FunPrec and TyOpPrec to represent the precedence of function
 arrow and type operators respectively, but currently we implement
 FunPred == TyOpPrec, so that we don't distinguish the two. Reason:
 it's hard to parse a type like
     a ~ b => c * d -> e - f

 By treating TyOpPrec = FunPrec we end up with more parens
     (a ~ b) => (c * d) -> (e - f)

 But the two are different constructors of TyPrec so we could make
 (->) bind more or less tightly if we wanted.
 }}}

 I propose we close this ticket - I tend to agree with the note that the
 extra parens increase readability.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13637#comment:3>
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