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2 points by fallintothis 5126 days ago | link | parent

Not to be snarky, but I linked to http://www.paulgraham.com/ilc03.html for a reason. One salient point (that's independent from annotate):

  arc> (let orig +
         (def + args
           (if (all acons args)
               (do (prn "Blah blah, special, blah blah")
                   (apply orig args))
               (apply orig args))))
  *** redefining +
  #<procedure: +>
  arc> (+ 1 2 3)
  6
  arc> (+ '(a b c) '(d e f))
  Blah blah, special, blah blah
  (a b c d e f)
  arc> (+ '(a b c) 1 2 3)
  Error: "car: expects argument of type <pair>; given 1"
The only things you might have trouble extending this way are macros (since any definition up to the point where you redefine it will have been expanded)

  arc> (mac m (x) `(do (prn "orig") ',x))
  #(tagged mac #<procedure: m>)
  arc> (def f () (m 5))
  #<procedure: f>
  arc> (let orig (rep m)
         (mac m (x)
           (if (number x)
               `(do (prn "redef") ',x)
               (orig x))))
  *** redefining m
  #(tagged mac #<procedure: m>)
  arc> (m "a string")
  orig
  "a string"
  arc> (m 5)
  redef
  5
  arc> (f)
  orig
  5
and names treated specially by the compiler (if, fn, quote, quasiquote, unquote, unquote-splicing, assign, nil, t).

Also relevant: http://awwx.ws/extend0.arc, http://awwx.posterous.com/defrule.



1 point by akkartik 5126 days ago | link

Are you suggesting we don't need annotations for anything that extend works with? That isn't how I read that essay at all.

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1 point by fallintothis 5126 days ago | link

I meant that

  (let orig f
    (def f args
      ; you can put ANY code you want in here
      ))
Hence, extend is independent from annotate: just as you can annotate without using extend, you can extend without using annotate. extend is just a byproduct of closures and first-class functions. Of course, combining annotate and extend lets you dispatch based on custom types.

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