[GHC] #10547: feature request: expanding type synonyms in error messages

[GHC]

#10547: feature request: expanding type synonyms in error messages
-------------------------------------+-------------------------------------
        Reporter:  osa1              |                   Owner:  osa1
            Type:  feature request   |                  Status:  new
        Priority:  low               |               Milestone:  7.12.1
       Component:  Compiler (Type    |                 Version:
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  D1016
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Comment (by osa1):

 So let's say I have these synonyms:

 {{{
 T5 = T4
 T4 = T3
 ...
 T0 = Int
 }}}

 and these types:

 {{{
 (T5, T3, X) and (T3, T5, Y)
 }}}

 ideally I want to report as "Expected (T3, T3, X) Found (T3, T3, Y)", did
 I get this right?

 So it's not just walking down two types together, because that would give
 us `(Int, Int, X)` and `(Int, Int, Y)`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10547#comment:3>
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