[GHC] #11673: Doesn't accept type

[GHC]

#11673: Doesn't accept type
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

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


Comment:

 Well, if you write
 {{{
 instance ... where
   id :: Transformer f f
   id = ...
 }}}
 then GHC tries to understand the signature you wrote.  Since `Transformer`
 poly-kinded, what you get is the signature
 {{{
 id :: forall i k. forall (f :: i -> k). Transformer f foo
 }}}
 But `Cat.id` doesn't have that type.

 So I think this is just what's expected.

 Can you suggest any improvement to the user manual that would make this
 clearer?

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11673#comment:1>
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