Arc is more like Common Lisp in that you can call whatever you want while expanding a macro, and if you make a mistake you might end up with an infinite regress of macroexpansion or something like that. Its macros are not hygienic which again creates room for certain kinds of bugs, but some of us here tend to think of those as learning experiences ^_^ whose benefits outweigh their pain.

Paul Graham has this to say about hygiene in the tutorial:

  Some people worry unduly about this kind of bug.  It caused the
  Scheme committee to adopt a plan for "hygienic" macros that was
  probably a mistake.  It seems to me that the solution is not to
  encourage the noob illusion that macro calls are function calls.
  People writing macros need to remember that macros live in the land
  of names.  Naturally in the land of names you have to worry about
  using the wrong names, just as in the land of values you have to
  remember not to use the wrong values-- for example, not to use zero
  as a divisor.

  (mac n-of (n expr)
    (w/uniq ga
      `(let ,ga nil
         (repeat ,n (push ,expr ,ga))
         (rev ,ga))))

It seems we don't particularly follow that rule here on the Arc Forum. For instance, a few of us have agreed that a certain behavior in Arc 3.1 is a bug: When we make a function call to a local variable, we don't want a global macro of the same name to take effect, which is what happens in Arc 3.1. If we were keeping locals and globals separate, we wouldn't even encounter this problem.

Which means that if we want to write macros that are hygienic, we can't write them in quite the way we see in arc.arc or the tutorial. If we're dedicated to hygiene, we might even want to rewrite arc.arc to fix its hygiene issues... but that's practically the whole language, so it effectively starts to be a new language project. The Anarki arc2.hygiene branch, Penknife, ar, Semi-Arc, and Nulan are several examples of Arc-based or Arc-inspired projects that pursued some kind of hygiene.

If we don't mind the lack of hygiene in arc.arc but only care about proper hygiene for our own new macros, it is possible to be diligent about hygiene in plain Arc 3.1 or Anarki:

  (mac n-of (n expr)
    (w/uniq ga
      (rep.let ga nil
         (rep.repeat n (rep.push expr ga))
         `(',rev ,ga))))

  (mac n-of (n expr)
    `( ',(fn (n expr)
             (let a nil
               (repeat n (push (expr) a))
               rev.a))
       ,n
       (fn () ,expr)))

  (mac qq-with args
    (let (body . rev-bindings) rev.args
      (let (vars vals) (apply map list (pair rev.rev-bindings))
        `(',list `',(fn ,vars ,body) ,@vals))))
  
  (mac n-of (n expr)
    (qq-with n n expr `(fn () ,expr)
      (let a nil
        (repeat n (push (expr) a))
        rev.a)))

However, there is a very simple change that can be made to the Arc compiler which would make hygienic macros easy to write.

The Arc compiler would have a big hash table which maps from global symbols to gensyms.

Whenever you define a global variable, it will create a new gensym and store it in the hash table.

When using the quasiquote syntax, it will lookup the variable in the hash table and will use the gensym rather than the symbol.

As an example, if you have this Arc program:

  (= foo 1)

  (mac bar ()
    `(+ foo 2))

  (= #<foo:1> 1)

  (mac #<bar:1> ()
    `(#<+:1> #<foo:1> 2))

Now the macro bar will always expand to the correct global variable foo, and therefore it is 100% hygienic.

If you want to intentionally break hygiene, you can simply do this:

  (mac bar ()
    `(+ ,'foo 2))

The advantages of the language are numerous: raw macro, short names, incredible library, awesome operators, right choice of data structures, etc.

Programming is my life. I like to think I'm a master of it. But I'm completely alone. Also I hate my jobs, I hate big companies, I hate bullshit, I hate TDD, I hate code reviews, I hate estimations; it's a pain man.

Poker, while definitely not as deep as software, is the exact opposite. They do TDD? I take money. They do code reviews? I take money. bullshit? a fountain of money...

I'm constantly looking for people to hack with as well. Some ideas:

a) We could work on anarki. For example, try out the latest version sometime when you have time and let me know if mktemp broke again on Windows. Help kinnard and me expand the install instructions for Anarki to Windows. Neither of us knows how to run Arc there, so this would be very valuable. These small-ish ideas might be the start of a larger project.