[GHC] #9497: Silent typed holes

[GHC]

#9497: Silent typed holes
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              Reporter:  merijn      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:  typed holes,
            Resolution:              |  warnings
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by goldfire):

 Replying to [comment:4 simonpj]:
 > Two issues with Richard's proposals:
 >
 >  * There is no way to switch off typed holes altogether, and revert to
 > {{{
 > Hole.hs:1:7: Pattern syntax in expression context: _
 > }}}
 >  Maybe that is OK.

 I think this is OK. It's conceivable that a user makes a typo in an
 identifier that begins with an underscore and will be very confused by the
 error message. But, that exact same scenario would happen today, unless
 the user also somehow knows to use an obscure compiler option (`-fno-warn-
 typed-holes`). One way to mitigate this problem is to have typed-hole
 error/warning messages link to a description of the feature.

 >
 >  * What does `-fno-warn-typed-holes` do in the absence of `-fdefer-
 typed-holes`?  No-op with a warning?
 >

 It suppresses typed-hole warnings, of which there would be none. This is
 the same behavior as other `-fno-warn-...` options, when the condition
 that is being suppressed doesn't happen. I'm not bothered here.

 >  * What does `-fwarn-typed-holes` do?  Perhaps just re-enable the
 warning after switching off all warnings with `-w`.

 Yep.

 One issue with this bikeshed color: having options `-fdefer-type-errors`
 and `-fdefer-typed-holes` forced users to remember the difference between
 `type` and `typed`. I think the choices here make sense (`type` in the
 first, `typed` in the second), but it is a little annoying.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9497#comment:5>
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