[GHC] #10963: Beginner-targeted language extension

[GHC]

#10963: Beginner-targeted language extension
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        Reporter:  kanetw            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       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:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 In a fit of frustration at the thought of teaching Haskell in a year's
 time without this feature, I've implemented it. Phab patch to be posted
 shortly. Here's the user's guide description. Bikeshedding and design
 improvements welcome.

 {{{
 .. ghci-cmd:: :type-def; (expression)
 .. ghci-cmd:: :td; (expression)

     Infers and prints the type of (expression), defaulting type variables
     if possible. In this mode, if the inferred type is constrained by
     any interactive class (``Num``, ``Show``, ``Eq``, ``Ord``,
 ``Foldable``,
     or ``Traversable``), the constrained type variable(s) are defaulted
     according to the rules described under :ghc-
 flag:`-XExtendedDefaultRules`.
     This mode is quite useful when the inferred type is quite general
 (such
     as for ``foldr``) and it may be helpful to see a more concrete
     instantiation.
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10963#comment:3>
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