[GHC] #9091: print and/or apply constraints when showing info for typed holes

[GHC]

#9091: print and/or apply constraints when showing info for typed holes
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        Reporter:  kosmikus                 |            Owner:
            Type:  feature request          |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler (Type checker)  |          Version:  7.8.2
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by simonpj):

 It would be easy to also show the in-scope "given" constraints.  But how
 would you like to see them.  For Ex 1, 2 can you show what error message
 you'd like to see?  Something like (for Ex 1)
 {{{
     Found hole ‘_’ with type: Bool
     Relevant bindings include
       y :: a (bound at THC.hs:4:5)
       x :: a (bound at THC.hs:4:3)
       f :: a -> a -> Bool (bound at THC.hs:4:1)
     Given constraints: Eq a
     In the expression: _
     In an equation for ‘f’: f x y = _

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9091#comment:1>
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