[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):

 As discussed in Hangouts, the problem is even more specific: it only
 appears for expressions entered at the GHCi prompt while defer-type-errors
 is active. Loading modules with defer-type-errors on, then turning it off
 and *then* evaluating expressions at the prompt works just fine.

 Hence, the quick fix for 8.6 will be to selectively disable deferred type
 checking for expressions entered interactively. This way, we will not
 disrupt any workflows (the error would have appeared right there and then
 one way or another), while still avoiding the crash.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14963#comment:22>
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