[GHC] #14584: Core Lint error

[GHC]

#14584: Core Lint error
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  TypeInType,
                                     |  DeferredTypeErrors
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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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"a492af06d3264530d134584f22ffb726a16c78ec/ghc"
 a492af06/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="a492af06d3264530d134584f22ffb726a16c78ec"
 Refactor coercion holes

 In fixing Trac #14584 I found that it would be /much/ more
 convenient if a "hole" in a coercion (much like a unification
 variable in a type) acutally had a CoVar associated with it
 rather than just a Unique.  Then I can ask what the free variables
 of a coercion is, and get a set of CoVars including those
 as-yet-un-filled in holes.

 Once that is done, it makes no sense to stuff coercion holes
 inside UnivCo.  They were there before so we could know the
 kind and role of a "hole" coercion, but once there is a CoVar
 we can get that info from the CoVar.  So I removed HoleProv
 from UnivCoProvenance and added HoleCo to Coercion.

 In summary:

 * Add HoleCo to Coercion and remove HoleProv from UnivCoProvanance

 * Similarly in IfaceCoercion

 * Make CoercionHole have a CoVar in it, not a Unique

 * Make tyCoVarsOfCo return the free coercion-hole variables
   as well as the ordinary free CoVars.  Similarly, remember
   to zonk the CoVar in a CoercionHole

 We could go further, and remove CoercionHole as a distinct type
 altogther, just collapsing it into HoleCo.  But I have not done
 that yet.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14584#comment:9>
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