[GHC] #10747: Infix pattern synonyms fail to parse (regression)

[GHC]

#10747: Infix pattern synonyms fail to parse (regression)
-------------------------------------+-------------------------------------
        Reporter:  heisenbug         |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------
Changes (by rwbarton):

 * priority:  normal => high
 * version:  7.11 => 7.10.1


Old description:

> {{{#!hs
> {-# LANGUAGE PatternSynonyms #-}
> pattern head `Cons` tail = head : tail
> }}}
>
> In v7.11 I get:
> {{{
> [1 of 1] Compiling Main             ( pat.hs, interpreted )
>
> pat.hs:2:14: parse error on input ?`?
>
> }}}
>
> In v7.10 I get:
> {{{
> *Main> :set -XPatternSynonyms
> *Main> let h `Cons` t = "ht"
> *Main> h
> 'h'
> *Main> t
> "t"
> }}}

New description:

 {{{#!hs
 {-# LANGUAGE PatternSynonyms #-}
 pattern head `Cons` tail = head : tail
 }}}

 In v7.10 I get:
 {{{
 [1 of 1] Compiling Main             ( pat.hs, interpreted )

 pat.hs:2:14: parse error on input ?`?

 }}}

 In v7.8 I get:
 {{{
 [1 of 1] Compiling Main             ( ph.hs, interpreted )
 Ok, modules loaded: Main.
 *Main> :set -XPatternSynonyms
 *Main> let h `Cons` t = "ht"
 *Main> h
 'h'
 *Main> t
 "t"
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10747#comment:3>
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