[GHC] #10321: GHC.TypeLits.Nat types no longer fully simplified.

[GHC]

#10321: GHC.TypeLits.Nat types no longer fully simplified.
-------------------------------------+-------------------------------------
        Reporter:  darchon           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.10.2
       Component:  Compiler (Type    |                 Version:  7.10.1
  checker)                           |                Keywords:  TypeLits
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  Other             |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by rwbarton):

 I think the behavior of when to expand/simplify type families may have
 changed intentionally in 7.10, but simplifying the type only as far as
 `Num a => Vec (2 + 1) a` certainly looks weird.

 I also note that the behavior is different if the value is first bound to
 a variable:
 {{{
 *Main> let x = (3:>4:>5:>Nil)
 *Main> :t x
 x :: Num a => Vec 3 a
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10321#comment:1>
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