[GHC] #10972: Add a :binfo (beginner info) GHCi command

[GHC]

#10972: Add a :binfo (beginner info) GHCi command
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        Reporter:  kanetw            |                Owner:  kanetw
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10963            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by kanetw):

 What kind of specializations should be displayed? Displaying every
 possible specialization is impractical even if we restrict to unary
 typeclasses (consider `Num`).

 I think specializing for types with special notation like `[]` or `(->)`
 would be most useful:
 {{{#!hs
 > :binfo find
 find :: Foldable t => (a -> Bool) -> t a -> Maybe a
 Specializations:
  t ~ [] -> find :: (a -> Bool) -> [a] -> Maybe a

 > :binfo first
 first :: Arrow a => a b c -> a (b, d) (c, d)
 Specializiations:
  a ~ (->) -> first :: (b -> c) -> (b, d) -> (c, d)
 }}}

 Having something like `find :: (a -> Bool) -> Set a -> Maybe a` doesn't
 really help a lot in my opinion.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10972#comment:2>
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