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3 points by vsingh 6154 days ago | link | parent

I suppose I ought to have written it like this the first time:

   (w/collect
      (each y whatever
         (awhen (pfft y) (collect (yo-mama (cons y it))))))
'w/collect' being the first new operator to result from our discussion.


1 point by kennytilton 6154 days ago | link

"w/collect' being the first new operator to result from our discussion."

Oh. Where can I find w/collect? And do you mean it has been added to Official Arc? I must be missing out on the action.

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4 points by almkglor 6153 days ago | link

It's not on the arc-wiki. However I can certainly imagine how it would look like as a naive implementation:

  (mac w/collect body
    `(rev:accum collect ,@body))
Here's a slightly more optimized form which removes the need to reverse and adds only one additional variable to the environment built by accum:

  (mac w/collect body
    (w/uniq (hd tl)
      `(let (,hd ,tl collect) nil
          (= collect
            (fn (x)
              (if hd (do (= (cdr tl) (cons x nil)) (= tl (cdr tl)))
                      (do (= hd (cons x nil)) (= tl hd)))
               x))
          ,@body
          ,hd)))

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