[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 simonpj):

 The code in `TcUnify` described in comment:8 is
 {{{
 implicationNeeded skol_tvs given
   | null skol_tvs
   , null given
   = -- Empty skolems and givens
     do { tc_lvl <- getTcLevel
        ; if not (isTopTcLevel tc_lvl)  -- No implication needed if we are
          then return False             -- already inside an implication
          else
     do { dflags <- getDynFlags       -- If any deferral can happen,
                                      -- we must build an implication
        ; return (gopt Opt_DeferTypeErrors dflags ||
                  gopt Opt_DeferTypedHoles dflags ||
                  gopt Opt_DeferOutOfScopeVariables dflags) } }
 }}}
 So you have to switch of all three of `Opt_DeferTypeErrors`,
 `Opt_DeferTypedHoles` and `Opt_DeferOutOfScopeVariables`.   But NB that
 ''the first implies the other two''; so I guess that you need to switch
 all three of them off in the workaround.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14963#comment:30>
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