[GHC] #13480: GHCi display visible type application

[GHC]

#13480: GHCi display visible type application
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        Reporter:  Iceland_jack      |                Owner:  Iceland_jack
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #8751             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 TODO See if you can easily generate a dependency tree of type class
 instances used for an expression. Quite often I delete instances to check
 which instance they make use of (especially with indirect dependencies). A
 famous case where this would help is `view _Just Nothing` which has a
 `Monoid` constraint and the connection is contrived (I haven't considered
 how this could be visualised):

 {{{
 ghci> :whichInst view _Just Nothing

 instance Monoid m => Applicative (Const m)
 ...
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13480#comment:2>
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