[GHC] #11049: Allow CallStacks to be hidden or cut

[GHC]

#11049: Allow CallStacks to be hidden or cut
-------------------------------------+-------------------------------------
           Reporter:  nomeata        |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #11035
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This is a spin off of #11035. I’d like to see a way for a function `foo`

  * use another function `bar` with a `(?_::CallStack)` constraint so that
 `bar` will _not_ print a call stack, and
  * use another function `bar` with a `(?_::CallStack)` constraint so that
 if `bar` prints a call stack, it will stop at the call to `foo`.

 This might be possible to implement with a special `rootCallStack ::
 CallStack` which is a value such that
 {{{
 x `pushCallStack` rootCallStack = rootCallStack
 }}}
 but
 {{{
 rootCallStack `pushCallStack` x = rootCallStack “:” x
 }}}
 as before and a call stack that consists of only a rootCallStack causes no
 stack trace to be printed.

 The use case is to provide the user of a library less cluttered call
 stacks that do not expose unhelpful details and allow her to quickly spot
 the relevant information.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11049>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler