[GHC] #11047: Provide call stacks in GHCi

[GHC]

#11047: Provide call stacks in GHCi
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        Reporter:  simonmar          |                Owner:  simonmar
            Type:  task              |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  GHCi              |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #545, #4837       |  Differential Rev(s):  Phab:D1407
       Wiki Page:                    |
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Comment (by simonmar):

 `:hist` doesn't really print a call stack, it just prints a history of the
 recent locations that execution passed through.  It was a hack because we
 didn't have real stack trace support.  We might even drop `:trace` or
 replace it with something better when we have stack traces.

 SCC-based stack traces don't expose lazy evaluation (or at least, if they
 do, it's a bug we should fix, so please let me know).  I'm using the same
 cost-centre-stack semantics in GHCi as we have in the profiling system.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11047#comment:5>
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