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4 points by almkglor 6073 days ago | link | parent

Right. So tell me, suppose I have a very, very old piece of code, a classic, like this:

   (def map1 (f xs)
    " Return a sequence with function f applied to every element in sequence xs.
      See also [[map]] [[each]] [[mappend]] [[andmap]] [[ormap]] "
    (if (no xs)
        nil
        (cons (f (car xs)) (map1 f (cdr xs)))))
Now suppose in the future some random guy creates an application focused on cars. Since the guy knows he won't use 'car and 'cdr (car? cdr? pfft. that's so low-level! use proper let destructuring, foo!), he's quite willing to reuse the name 'car as a variable:

  (let car (get-user-car)
    (map1 color-wheel car!wheels))
Oops! map1's car function got overridden!

This is a rather contrived example, but hey, believe me: it'll happen, and it won't be as obvious as that. That's why dynamic variables are explicit in CL. That's why the default binding will be static.

Now if someone wants to explicitly have dynamic variables, it's already done. http://arclanguage.com/item?id=2497



1 point by jazzdev 6072 days ago | link

>Now suppose...

  (let car (get-user-car)
    (map1 color-wheel car!wheels))
>Oops! map1's car function got overridden!

That's a good argument. I can see the havoc that would result.

Still, I'm willing to risk that so that I have the option to do something like:

  (with (ocar car car-counter 0)
    (let car (fn (xs) (++ car-counter) (ocar xs))
      (map1 color-wheel car!wheels))
    (prn "map1 called car " car-counter " times"))

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