Arc Forum | "As I see it, the dot (car.ls) is syntactic sugar for applying a one arg functio...

Arc Forum

5 points by Pauan 4611 days ago | link | parent

"As I see it, the dot (car.ls) is syntactic sugar for applying a one arg function? Pretty clever!"

Arc has the following ssyntax:

  foo.bar     -> (foo bar)
  foo!bar     -> (foo 'bar)
  
  (~foo 1)    -> (no (foo 1))
  (foo:bar 1) -> (foo (bar 1))
  (foo&bar 1) -> (and (foo 1) (bar 1))

To be honest, I only use the ".", "!", and ":" ssyntax. Also, "~", ":", and "&" work even when they're not in functional position:

  (map ~foo ...)
  (map foo:bar ...)
  (map foo&bar ...)

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"Use of iso. Don't know why I used is.. Question I had, can '=' be use as a comparison operator?"

The only difference between "is" and "iso" is that "iso" recursively checks lists:

  (is  (list 1 2 3) (list 1 2 3))  ; nil
  (iso (list 1 2 3) (list 1 2 3))  ; t

"=" is always used for assignment, never for comparison. The only built-in equality function is "is", and "iso" is defined using "is".

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"Also I get your use of 'else, but not exactly sure how it passes."

Like most Lisps, Arc has a datatype called "symbol", which is roughly equivalent to an "identifier" in other languages. Normally, if you use "else" it will refer to the variable "else", but if you use quote, it will be the symbol "else":

  else   ; variable
  'else  ; symbol

The rule for booleans in Arc is that the symbol "nil" is false, and everything else is true. The symbol "else" is not equal to the symbol "nil", therefore it is true.

The reason why akkartik used "else" is a personal style difference. It's idiomatic to just leave it off:

  (if 1    ; if
        2  ; then
      3    ; if
        4  ; then
      5)   ; else

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"Now, if I understood well, there are two major forks, one you are working on, that would be wart, and anarki (mistaken already?)."

wart isn't a fork of Arc, it's a different language which has some similarities with Arc.

You can find a bunch of Arc info here:

https://sites.google.com/site/arclanguagewiki/

In particular, anarki is a true fork of Arc, which has diverged a lot, so don't expect much compatibility with existing Arc programs. But if you want all kinds of new features, I'd recommend it. I haven't used it myself though, so that's about all I can say about it.

Arc/Nu[1] is a fork of Arc I created, which should be mostly compatible with Arc 3.1, but cleans up the compiler and adds in a few new things. Naturally I recommend using this if you want something similar to Arc 3.1.

Then there's various other implementations of Arc, such as jarc and Rainbow, and an incomplete C implementation of Arc called Arcueid.

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* [1]: https://github.com/Pauan/ar

3 points by akkartik 4611 days ago | link

  (if 1    ; if
        2  ; then
      3    ; if
        4  ; then
      5)   ; else

Yeah, it's problematic how to indent the "5". The above way makes it look like a test rather than an action, and indenting it further makes it seem like part of the same block as 4.

You can tell that there's no idiomatic way to deal with this because the arc/HN codebase is schizophrenic, using both in different places.

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2 points by rocketnia 4611 days ago | link

Well, I always indent it in one of two ways, depending on how much room I have:

This style may have drawbacks, but I stubbornly use it anyway. :-p

  (list:if 1   ; misaligned condition
    (do a b c
      (d e f))
      (is x 0)  ; looks like part of the previous expr
    4
    5)

EDIT: Changed "I like it most of the time anyway" to "I stubbornly use it anyway." XD Somebody upvoted me before my edit....

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1 point by akkartik 4610 days ago | link

I understood what you meant, rocketnia ^_^

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2 points by Pauan 4611 days ago | link

For Nulan, my current thought is that multi-case "if" is too confusing with indentation, so the above would be written like this:

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