[GHC] #10963: Beginner-targeted language extension

[GHC]

#10963: Beginner-targeted language extension
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           Reporter:  kanetw         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 FMP significantly complicated type signatures such as `length :: Foldable
 t => t a -> Int`, which makes teaching Haskell more difficult.

 I propose a language extension `-XBeginner` which instructs GHC(i) to
 specialize `Foldable` and `Traversable` to `[]` when possible and in case
 of an ambiguous instance, default those to `[]`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10963>
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