[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 simonpj):

 I looked at this too.  Turns out that we do normalise types for inferred
 let-bindings; see line 661 of `TcBinds`, the call to `normaliseType` in
 `mkInferredPolyId`.  The explanation there is "to make the type as simple
 as possible". See commit `a6e7654b`.  It doesn't mention a Trac ticket.

 So I think our guess is that normalising is usually the Right Thing.  It
 seems inconsistent not to do it here too.  If we want to, the spot is in
 `TcRnDriver.tcRnExpr`

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10321#comment:3>
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