[GHC] #12668: Program that fails Core Lint terribly

[GHC]

#12668: Program that fails Core Lint terribly
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             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:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"eefe86d96d40697707c3ddfb9973a30a1897241f/ghc" eefe86d/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="eefe86d96d40697707c3ddfb9973a30a1897241f"
 Allow levity-polymorpic arrows

 This cures Trac #12668 (and cures the Lint errors you get from
 Trac #12718).

 The idea is explained in Note [Levity polymorphism], in Kind.hs
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12668#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler