[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:  tdammers
            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 tdammers):

 Replying to [comment:13 goldfire]:
 > I actually proposed doing exactly that when working this out with Simon.
 The problem is that doing so would ruin error messages, because we could
 report errors only with respect to the expanded syntax, instead of what
 the user actually wrote.

 My gut feeling (by all means correct me if I'm wrong!) is that this would
 still amount to a more elegant solution, everything considered. We would
 have to extend `HsSyn` to retain the original (sugared) notation, and
 treat such annotated syntax specially when printing error messages, but as
 far as type checking etc. are concerned, I would expect this to be mostly
 transparent.

 Personally, I wouldn't even mind getting error messages in desugared form,
 but I can understand if others feel strongly about this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14963#comment:18>
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