[GHC] #12366: Use TypeOperators for pattern synonyms?

5 Jul 2016

      #12366: Use TypeOperators for pattern synonyms?
-------------------------------------+-------------------------------------
           Reporter:  dubiousjim     |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (Parser)                           |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 With the language setting `-XTypeOperators`, I can use ''varsym''
 expressions, like `<|`, as type constructors. I would expect that we would
 then also be able to use them as pattern synonyms; but we can't. This is a
 request for that to become possible.

 {{{#!hs
 {-# LANGUAGE TypeOperators, PatternSynonyms #-}

 module Main where

 pattern (<|) x xs = Just (x, xs)

 main = case Just (1, [2,3]) of { Nothing -> putStrLn "Nothing"; y <| ys ->
 print y }
 }}}

 gives a parse error.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12366
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler