[GHC] #5296: Add explicit type applications

[GHC]

#5296: Add explicit type applications
-------------------------------------+-------------------------------------
        Reporter:  dsf               |                Owner:  goldfire
            Type:  feature request   |               Status:  closed
        Priority:  low               |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.0.3
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  typecheck/should_compile/Vta{1,2}
                                     |  typecheck/should_fail/VtaFail
      Blocked By:  1897              |             Blocking:  10770
 Related Tickets:  #4466             |  Differential Rev(s):  Phab:D1681
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 It depends on what ambiguity means. In a language with visible type
 application,

 {{{
 foo :: (Show a, Read a) => String -> String
 }}}

 can be called quite easily. Thus the ambiguity check seems unhelpful here.
 Thus the decision to have `TypeApplications` turn on
 `AllowAmbiguousTypes`.

 I do see what you're getting at. Perhaps this is the wrong design, and I'm
 happy to think about changing it (although it does seem a bit late). I
 will say that if you do want the ambiguity check, you can always use
 `NoAllowAmbiguousTypes`.

 If you wish to pursue the issue, I think a good next step is posting to
 ghc-devs to see what others think.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5296#comment:30>
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