[GHC] #14610: newtype wrapping of a monadic stack kills performance

[GHC]

#14610: newtype wrapping of a monadic stack kills performance
-------------------------------------+-------------------------------------
        Reporter:  mrkkrp            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14620            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by nomeata):

 >  Operationally the transformation makes sense, but it's not well typed.
 I have no idea how to fix this.

 So am I right to say “we forbid polymorphic return types because we cannot
 prove it to be sound, even though we know it would not actually crash if
 we did allow it”?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14610#comment:16>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler