[GHC] #15879: Make UniqDSet a newtype

[GHC]

#15879: Make UniqDSet a newtype
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        Reporter:  sgraf             |                Owner:  (none)
            Type:  task              |               Status:  closed
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler          |              Version:  8.6.2
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13114            |  Differential Rev(s):  Phab:D5313
       Wiki Page:                    |
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Comment (by Krzysztof Gogolewski <krz.gogolewski@…>):

 In [changeset:"17e771e17e2374f50f39948955e583760f28351f/ghc"
 17e771e1/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="17e771e17e2374f50f39948955e583760f28351f"
 More compact Outputable instance for `Uniq(D)Set`

 Summary:
 Until now, `UniqSet` and `UniqDSet` inherited their `Outputable`
 instances from `UniqFM` and `UniqDFM`.

 That made for verbose and redundant output. This patch rectifies
 that by pretty-printing these sets in common math notation.
 E.g., previously, we would render `UniqSet`s like this:

     [s2fE :-> x_s2fE, s2fF :-> y_s2fF, s2fG :-> z_s2fG, s2fH :-> g_s2fH]

 Now, they're are printed like this:

     {x_s2fE, y_s2fF, z_s2fG, g_s2fH}

 Reviewers: simonpj, bgamari, AndreasK, dfeuer, osa1

 Reviewed By: osa1

 Subscribers: osa1, rwbarton, carter

 GHC Trac Issues: #15879

 Differential Revision: https://phabricator.haskell.org/D5315
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15879#comment:4>
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