[GHC] #8501: Improve error message when using rec/mdo keyword without RecursiveDo extention.

[GHC]

#8501: Improve error message when using rec/mdo keyword without RecursiveDo
extention.
-------------------------------------+-------------------------------------
        Reporter:  shelarcy          |                Owner:  ruperthorlick
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
  (Parser)                           |
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  parser/should_fail/T8501a
      Blocked By:                    |             Blocking:
 Related Tickets:  #3968             |  Differential Rev(s):  Phab:D3271
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"5856c564dff79a5c2b6a92b1c6c350798b538da3/ghc"
 5856c564/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5856c564dff79a5c2b6a92b1c6c350798b538da3"
 Fixed error messages for RecursiveDo (#8501)

 Changes in a few different places to catch several different
 types of error related to RecursiveDo

 Signed-off-by: Rupert Horlick <ruperthorlick at gmail.com>

 Test Plan: Three test cases, with further tests in comments

 Reviewers: austin, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D3271
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8501#comment:5>
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