[GHC] #10569: Optionally treat an out-of-scope variable like a typed hole

[GHC]

#10569: Optionally treat an out-of-scope variable like a typed hole
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        Reporter:  simonpj           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
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 ertes):

 I'm using `-W` and `-fdefer-typed-holes`. Now ''any'' out of scope
 variable will cause my program to crash at run-time rather than just
 telling me that something is out of scope. Since I often have a lot of
 pending warnings to deal with, I don't see the scope warnings before run-
 time, and then it can take arbitrarily long to pop up, and I have to start
 the development cycle all over.

 Holes (a development tool) and scope errors (a programmer mistake) are
 fundamentally different things, and treating them as the same massively
 disrupts my workflow. In fact, after I explained this phenomenon in
 #haskell on Freenode, we first thought it's a GHC bug.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10569#comment:7>
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