[GHC] #5296: Add explicit type applications

[GHC]

#5296: Add explicit type applications
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        Reporter:  dsf               |                   Owner:  goldfire
            Type:  feature request   |                  Status:  new
        Priority:  low               |               Milestone:  8.0.1
       Component:  Compiler (Type    |                 Version:  7.0.3
  checker)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:  1897              |                Blocking:
 Related Tickets:  #4466             |  Differential Revisions:  Phab:D1138
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Comment (by goldfire):

 Thanks for the suggestion. Unfortunately, I think that `?a` looks too much
 like !ImplicitParams. But I do like the general idea.

 Here's a very, very radical thought: what if we use color? We could print
 `forall b. Num a => b -> (a, b)` but put `a` in a different color. (Even
 though it's a bit of a lie, I prefer putting the `forall b` before the
 `Num a`, only because Haskellers are much more used to that ordering.)
 Non-colored terminals still get all the information they need: that `b` is
 available for type application whereas `a` is not. But someone with color
 could see the needed information very easily.

 But something tells me it would be a major plumbing job to get color
 output... :(

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5296#comment:24>
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