[GHC] #8739: ($) returning kind # no longer type checks

[GHC]

#8739: ($) returning kind # no longer type checks
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        Reporter:  NeilMitchell      |            Owner:
            Type:  bug               |           Status:  infoneeded
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"5dd1cbbfc0a19e92d7eeff6f328abc7558992fd6/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5dd1cbbfc0a19e92d7eeff6f328abc7558992fd6"
 Allow ($) to return an unlifted type (Trac #8739)

 Since ($) simply returns its result, via a tail call, it can
 perfectly well have an unlifted result type; e.g.
     foo $ True    where  foo :: Bool -> Int#
 should be perfectly fine.

 This used to work in GHC 7.2, but caused a Lint failure.  This patch
 makes it work again (which involved removing code in TcExpr), but fixing
 the Lint failure meant I had to make ($) into a wired-in Id.  Which
 is not hard to do (in MkId).
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8739#comment:7>
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