[GHC] #15704: Different saturations of the same polymorphic-kinded type constructor aren't seen as apart types

[GHC]

#15704: Different saturations of the same polymorphic-kinded type constructor
aren't seen as apart types
-------------------------------------+-------------------------------------
        Reporter:  mniip             |                Owner:  mniip
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.6.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9371             |  Differential Rev(s):  Phab:D5206
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by mniip):

 Replying to [comment:8 simonpj]:
 > I like this fix. But can I ask about this in `Unify.hs`:
 > {{{
 > -    go _ _ = maybeApart  -- See Note [Lists of different lengths are
 MaybeApart]
 > +    go _ _ = surelyApart
 > +      -- Possibly different saturations of a polykinded tycon (See Trac
 #15704)
 > }}}
 > I don't see where in this ticket we discuss "possibly different
 saturations of a polykinded tycon".
 >
 > It'd be more direct simply to give an example.  Do you have in mind
 this?
 > {{{
 > T :: forall k. Type -> k
 >
 > ty1 = T Type Int              :: Type
 > ty2 = T (Type->Type) Int Int  :: Type
 > }}}
 > Or did you have other examples in mind?
 >
 > Thanks

 The `D` in the ticket is a polykinded tycon:

 {{{#!hs
 ty1 = D @(Type -> Type) Int               :: Type
 ty2 = D @(Type -> Type -> Type) Int Bool  :: Type
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15704#comment:9>
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