[GHC] #11298: Implicit call stack empty in instance declarations

[GHC]

#11298: Implicit call stack empty in instance declarations
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        Reporter:  pikajude          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by gridaphobe):

 I updated the user guide as part of the rewrite, the current version is
 hosted [http://downloads.haskell.org/~ghc/master/users-
 guide//glasgow_exts.html#implicit-callstacks here].

 It does mention that a bare `?loc :: CallStack` will be resolved to the
 empty stack ("GHC will never report an unbound implicit CallStack, and
 will instead default such occurrences to the empty CallStack.")

 It also describes `getCallStack` for extracting the list of call-sites,
 and `freezeCallStack` for preventing the addition of further call-sites.
 There are a couple other API functions (`push` and `pop`) that are only
 mentioned in the haddocks, but I think that's ok as they're pretty self-
 explanatory.

 Ack, I just noticed that the formatting is a bit screwy towards the end of
 the section, I'll send a patch to clean it up. If you have any
 comments/suggestions on the content itself I'd be happy to incorporate
 them.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11298#comment:7>
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