[GHC] #15034: Desugaring `mdo` moves a `let` where it shouldn't be

[GHC]

#15034: Desugaring `mdo` moves a `let` where it shouldn't be
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        Reporter:  parsonsmatt       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:  RecursiveDo
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by parsonsmatt):

 > That is indeed odd. Are you sure your example is right in comment:2? You
 don't even use theUsual before its definition in the "However, when I
 move..." version.

 Yes. [https://github.com/parsonsmatt/mesa-
 verde/blob/81d2fb68ec87ff3f97eed1463f86f5f7e0b77240/src/MesaVerde/Internal.hs
 This is a repository] containing all of the code and definitions.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15034#comment:4>
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