[GHC] #8064: Warning out when "undefined" value has been used.

[GHC]

#8064: Warning out when "undefined" value has been used.
-------------------------------------+-------------------------------------
        Reporter:  freizl            |                Owner:
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:  wontfix           |             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:                    |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 It's much better to use
 [https://downloads.haskell.org/~ghc/7.10.3/docs/html/users_guide/typed-
 holes.html typed holes] instead of `undefined` for this purpose, since it
 will give you the warning you requested.

 {{{#!hs
 f :: Int
 f = _

 main = print f
 }}}

 {{{
 $ ghc-7.10.3 -fdefer-typed-holes Test.hs
 [1 of 1] Compiling Main             ( Test.hs, Test.o )

 Test.hs:2:5: Warning:
     Found hole ‘_’ with type: Int
     Relevant bindings include f :: Int (bound at Test.hs:2:1)
     In the expression: _
     In an equation for ‘f’: f = _
 Linking Test ...
 }}}

 To suppress the warning, use `-fno-warn-typed-holes`.

 Given that these flags now exist, I'm closing this as wontfix.

 See #11482 for a request to turn `-fdefer-typed-holes` on by default.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8064#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler