[GHC] #14963: ghci -fdefer-type-errors can't run IO action from another module

[GHC]

#14963: ghci -fdefer-type-errors can't run IO action from another module
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        Reporter:  elaforge          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.2
       Component:  GHCi              |              Version:  8.4.1
      Resolution:                    |             Keywords:
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 goldfire):

 There's always room for simplification, of course, but I think the room
 here is limited. This whole mechanism came into being when `ExpType`s were
 introduced. `ExpType`s are "holes" -- places to write a type once we infer
 it; they replaced `SigmaTv` tyvars that were used previously. I forget
 what aspect of `ExpType`s specifically forced the rewrite of rebindable
 syntax, but I do remember that this was more-or-less forced.

 The reason for the complication is that we want to allow for the
 possibility that `(>>=) :: blah -> (forall x. x -> x) -> wurble`, where
 the arguments might have a higher-rank type. This, in turn, requires
 skolemization while type-checking. That problem with the current setup is
 that the two arguments are checked in the same `thing_inside`, where they
 should really be in ''different'' contexts. But that would make the whole
 scheme even more complicated.

 So I'm a bit stuck really on how you would want to simplify this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14963#comment:10>
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