[GHC] #10963: Beginner-targeted language extension

[GHC]

#10963: Beginner-targeted language extension
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        Reporter:  kanetw            |                Owner:
            Type:  feature request   |               Status:  patch
        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):  Phab:D2136
       Wiki Page:                    |
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Comment (by goldfire):

 Thanks for linking to that. There may be two questions here:

 1. Do we want 1 specialization or many? I have to say I really like using
 the `default` list to prescribe the specializations, but perhaps another
 criterion (like load order, as originally proposed in the linked-to email)
 can be used.

 2. Do we want the output to come straight from `:type`, which would make
 every use of that very common command much longer?

 Re (1): I chose to produce 1 specialization for two reasons:

 A. Suppose we have a type constrained by `(Foldable f, Num a) => ...`. If
 we start printing out multiple specializations, we get a combinatorial
 number of them. Where do we cut this off? How are they ordered?

 B. Doing just 1 specialization could use the built-in defaulting mechanism
 very, very easily. Anything else would be quite a bit more challenging, I
 think. This isn't a reason to avoid other designs, exactly, but a point I
 wanted to make here.

 And, yes, I agree with comment:8 (written concurrently with this one) that
 we should seek more input. I'll put together that wiki page and post more
 broadly later today.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10963#comment:9>
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