[GHC] #13635: Incorrect result at runtime with list comprehensions in that case

[GHC]

#13635: Incorrect result at runtime with list comprehensions in that case
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        Reporter:  vanto             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      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 bgamari):

 vanto, why, concretely, do you think this is irrational? In general it is
 impossible for the compiler to know whether any given subexpression of
 your program will be evaluated. Consequently, we make no effort to adjust
 error messages for reachability (except when reachability can be
 determined by type information, e.g. pattern matching on a GADT).

 Typed holes are intended to be an aid to development and really shouldn't
 be found in production code. GHC's default behavior, like that of most
 compilers, is to assume the user is compiling for a production setting.
 The compiler's default treatment of typed holes reflects this. If you want
 the program to compile despite holes then we offer `-fdefer-typed-holes`.
 If you feel like this default should be changed then perhaps we can
 discuss this, but I'll admit I'm rather skeptical.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13635#comment:3>
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