[GHC] #10193: TypeRep Show instance doesn't add parens around type operators

26 Mar 2015

      #10193: TypeRep Show instance doesn't add parens around type operators
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              Reporter:              |             Owner:
  pawel.nowak                        |            Status:  new
                  Type:  bug         |         Milestone:
              Priority:  normal      |           Version:  7.10.1-rc3
             Component:              |  Operating System:  Unknown/Multiple
  libraries/base                     |   Type of failure:  Incorrect result
              Keywords:              |  at runtime
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 The following code

 {{{#!hs
 {-# LANGUAGE AutoDeriveTypeable #-}
 {-# LANGUAGE TypeOperators #-}
 import Data.Typeable

 data a :*: b = Pair a b

 main = print (typeOf (Pair 'a' 'b'))
 }}}

 prints

 {{{#!hs
 :*: Char Char
 }}}

 which is not valid Haskell. I belive it should print

 {{{#!hs
 (:*:) Char Char
 }}}

 In my particular case I am using Hint to interpret a type involving type
 operators. Hint uses showed TypeRep as a type annotation:

 {{{#!hs
 let type_str = show $ Data.Typeable.typeOf wit
 ...
 let expr_typesig = concat [parens e, " :: ", type_str]
 }}}
 What results in a parse error.

 I can write a patch if someone confirms that's the desired behavior and
 doesn't break anything.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10193
GHC http://www.haskell.org/ghc/
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