[GHC] #12701: Eta reduce type synonyms when possible

[GHC]

#12701: Eta reduce type synonyms when possible
-------------------------------------+-------------------------------------
        Reporter:  ezyang            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  backpack
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 I'm -1 on this change, as it is very easy for a user to specify that they
 want eta-reduction. With this change, partially applying a type synonym
 would sometimes work and sometimes not, in ways that are perhaps
 surprising to users.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12701#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler