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

[GHC]

#10321: GHC.TypeLits.Nat types no longer fully simplified.
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        Reporter:  darchon           |                   Owner:
            Type:  bug               |                  Status:  infoneeded
        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 goldfire):

 But yet we take (significant) pains not to look through type synonyms when
 reporting errors... we even avoid looking through type synonyms when
 normalizing!

 So, is the general idea that vanilla type synonyms are preferred over
 their RHSs, but reducing type families is better than leaving them
 unreduced? Perhaps. I have no objection to this. It is a little odd that
 changing a vanilla type synonym to a closed type family with one
 (universal) equation would change behavior, but this is all pretty-
 printing and heuristic anyway, so that's not too bad.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10321#comment:4>
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