[GHC] #8411: TypeSynonymInstances with partial type

[GHC]

#8411: TypeSynonymInstances with partial type
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        Reporter:  wvv                        |            Owner:
            Type:  bug                        |           Status:  closed
        Priority:  normal                     |        Milestone:
       Component:  Compiler                   |          Version:  7.6.3
      Resolution:  invalid                    |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Changes (by monoidal):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Unfortunately, this is by design. Partial application of type synonyms is
 highly nontrivial; if done, it would require a large upheaval of type
 inference, and add a lot of complexity. For example, how GHC could know
 whether given `return :: a -> (a,a)`, is `Monad ((,) a)` or `Monad (RTuple
 a)` required? The situation gets much more complicated with larger
 synonyms, and things get ugly. I suggest to ask this question on haskell-
 cafe or IRC and leave two links found by a google search: #785,
 http://stackoverflow.com/questions/4922560/.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8411#comment:1>
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