Arc Forumnew | comments | leaders | submitlogin
3 points by rkts 5929 days ago | link | parent

  (def greduce (iter)
    (fn (f xs y)
      (iter (fn args (= y (apply f y args))) xs)
      y))

  arc> (greduce.map + '(1 2 3) 0)
  6
  arc> (greduce.maptable (fn (y k v) (+ y v)) (obj 'a 1 'b 2 'c 3) 0)
  6
  ; etc...


5 points by rkts 5929 days ago | link

I guess I should clarify this a bit. In other languages (e.g. OCaml), it's conventional for each data structure to provide an iterator and a fold/reduce function. In Arc, the convention seems to be to provide iterators but not folds. The above code shows that it's sufficient only to have iterators, and a left fold can be automatically derived.

Alternatively, we could have data structures provide a left fold and automatically derive an iterator:

  (def giter (fold)
    (fn (f xs)
      (fold (fn (y . args) (apply f args) nil) xs nil)))
Thus, (giter:greduce f) == f, and (greduce:giter g) == g.

-----

2 points by drcode 5929 days ago | link

thanks- This is interesting information for me.

-----