[GHC] #12696: Exception gives not enough information to be useful

[GHC]

#12696: Exception gives not enough information to be useful
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        Reporter:  flip101           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  exception
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 flip101):

 Maybe a test case is not needed to help the issue along .. i discovered
 some more things

 {{{
 λ> :trace main
 Stopped in <exception thrown>, <unknown>
 _exception :: e = _
 λ> :print _exception
 _exception = (_t1::e)
 λ> seq _exception ()
 ()
 λ> :p _exception
 _exception = GHC.Exception.SomeException
                (GHC.Exception.ErrorCallWithLocation (_t9::String)
 (_t10::String))
 λ> _t9
 "Data.Data.fromConstr"
 λ> _t10
 ""
 }}}

 https://hackage.haskell.org/package/base-4.9.0.0/docs/src/Data.Data.html#fromConstr

 I would say this pretty much points to the origin of the exception. I
 found out about the seq-trick after another read of the debugging wiki.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12696#comment:8>
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