undefined | Better HN

0 pointssago7y ago0 comments

I don't know Arc, so this confuses me:

  arc> (map l '(0 1 2))
  (1 2 3)

What is the logic here? Is l made into a function that holds state and returns each element in turn (like an iterator function)? Because I would've expected:

  arc> (map l '(0 1 2))
  ((1 2 3) (1 2 3) (1 2 3))

In what way is map being applied here?

0 comments

sagoOP7y ago

After RTFM, I can answer my own question:

> In Arc, data structures can be used wherever functions are, and they behave as functions from indices to whatever's stored there.

(quoted from the Arc tutorial)

   arc> (l 0)
   1

and so on. So the GP makes sense.

dmead7y ago

that's confusing as hell. there's a reason this didn't take off (Besides the competition from clojure)

etatoby7y ago

I don't like the Arc language because it's dynamically typed and thus inherently unsafe (see other threads for this sort of discussion.)

But I like this particular feature. If you think about it, an array is a mathematical function, or map, from indices to values. So it makes sense to be able to apply it to indices to get the respective values.

1 more reply

quadcore7y ago

It's kinda cool to be able to write (myarray i).

ScottBurson7y ago

I think the list '(0 1 2) is behaving like the function — in CL syntax, sorry, I don't know Arc — (lambda (x) (elt '(0 1 2) x)). That is, the list is being treated as a sequence, which is a function from each index to the corresponding element.

jacobush7y ago

Is PicoLisp the same?

j / k navigate · click thread line to collapse