[GHC] #16339: Cannot put (.) or (!) into an export list

[GHC]

#16339: Cannot put (.) or (!) into an export list
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.7
  (Parser)                           |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  GHC rejects
  Unknown/Multiple                   |  valid program
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Thanks to recent work in GHC HEAD, it is now possible to define type
 operators named `(.)` and `(!)`:

 {{{#!hs
 type (f . g) x = f (g x)
 type x ! f = f x
 }}}

 However, I was surprised to discover that it's not possible to put them in
 an export list! That is to say, this program doesn't parse:

 {{{
 {-# LANGUAGE TypeOperators #-}
 module Bug (type (.), type (!)) where

 type (f . g) x = f (g x)
 type x ! f = f x
 }}}
 {{{
 $ ~/Software/ghc4/inplace/bin/ghc-stage2 --interactive Bug.hs
 GHCi, version 8.7.20190219: https://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci

 Bug.hs:2:19: error: parse error on input ‘.’
   |
 2 | module Bug (type (.), type (!)) where
   |                   ^
 }}}

 This problem appears to be specific to the `(.)` and `(!)` type operators,
 since any other type operator will work in its place:

 {{{#!hs
 {-# LANGUAGE TypeOperators #-}
 module Works (type (&)) where

 type (f & g) x = f (g x)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16339>
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