[GHC] #10249: Suboptimal error message with deferred type errors

[GHC]

#10249: Suboptimal error message with deferred type errors
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              Reporter:              |             Owner:
  Iceland_jack                       |            Status:  new
                  Type:  feature     |         Milestone:
  request                            |           Version:  7.10.1
              Priority:  normal      |  Operating System:  Unknown/Multiple
             Component:  GHCi        |   Type of failure:  None/Unknown
              Keywords:              |        Blocked By:
          Architecture:              |   Related Tickets:
  Unknown/Multiple                   |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 {{{#!hs
 $ ghci -fdefer-type-errors -ignore-dot-ghci
 GHCi, version 7.10.0.20150316: http://www.haskell.org/ghc/  :? for help
 Prelude> _

 <interactive>:2:1: Warning:
     Found hole ‘_’ with type: IO t0
     Where: ‘t0’ is an ambiguous type variable
     In the first argument of ‘GHC.GHCi.ghciStepIO ::
                                 IO a_aly -> IO a_aly’, namely
       ‘_’
     In a stmt of an interactive GHCi command:
       it <- GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly _
 *** Exception: <interactive>:2:1:
     Found hole ‘_’ with type: IO t0
     Where: ‘t0’ is an ambiguous type variable
     In the first argument of ‘GHC.GHCi.ghciStepIO ::
                                 IO a_aly -> IO a_aly’, namely
       ‘_’
     In a stmt of an interactive GHCi command:
       it <- GHC.GHCi.ghciStepIO :: IO a_aly -> IO a_aly _
 (deferred type error)
 Prelude>
 }}}

 It should ideally not expose `ghciStepIO` to the user.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10249>
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