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2 points by jsgrahamus 631 days ago | link | parent

Thanks. So, how do you get the 2 results from func1 into latitude and longitude?


2 points by akkartik 631 days ago | link

My code snippet is doing that. The let is doing a sort of pattern matching and binding latitude to the first element of the result, and longitude to the second.

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2 points by zck 631 days ago | link

I'll explain a little further, because Arc's let is unusual. Unlike most Lisps, the variable-value pairs are not themselves enclosed in parentheses.

In this code:

    (let (latitude longitude) (func1 a b c)
We're not binding latitude to the value of longitude, but binding that whole thing to the return value of (func1 a b c).

A simpler example:

    (let (name score) '("Steve Wiebe" 1064500)
      (prn name " was the first person to score over a million points in Donkey Kong, with a score of " score))
This prints:

    Steve Wiebe was the first person to score over a million points in Donkey Kong, with a score of 1064500

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3 points by jsgrahamus 631 days ago | link

And, of course, the "regular" form of arc has no parentheses:

  arc> (let hat 5 (prn "hat = " hat))
  hat = 5
  "hat = "
  arc>

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2 points by jsgrahamus 631 days ago | link

I thought that let looked odd, because I thought that with a let in arc, you had 1 variable/value pair. Thanks, zck, for pointing out the difference. And thanks, akkartik, for repeatedly telling me this.

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2 points by waterhouse 628 days ago | link

The corresponding macro in Common Lisp has an 18-character name.

  ; SBCL
  * (destructuring-bind (x y) '(1 2) (+ x y))
  3
  ; Arc
  arc> (let (x y) '(1 2) (+ x y))
  3

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