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2 points by Pauan 4791 days ago | link | parent

It only took about 30-60 minutes to implement it. My Arc interpreter now supports both forms of optional parameters:

  (def foo (a b (o c) (o d) . e))  ; works
  (def foo (a b . (c d . e)))      ; works
I plan to support this style of optionals too:

  (def foo (a b ? o d . e))
This could all change, though. I haven't yet seen the Perfect Holy Grail for optional arguments. I kinda like Python's take on it, though:

  def foo(a, b, c=None, d=None, *e):
      pass
Which would be this, in Arc:

  (def foo (a b c=nil d=nil . e))
Which would expand to:

  (def foo (a b (= c nil) (= d nil) . e))


1 point by Pauan 4788 days ago | link

Okay, scrap that. Here's my new plan:

Make all arguments optional, as per evanrmurphy's suggestion. I'll still support the (o foo) form for backwards compatibility, but I think it has so many problems that it really should be avoided.

This isn't final, but I figure the simplicity of not supporting required parameters will be a net gain most of the time. If you really need required parameters, it's possible to write macros that do the checks at run-time. I might even provide such a macro in arc.arc so you don't have to write it yourself.

Also, for telling Arc what the default is (it's normally nil), you use the (= foo 'bar) form, like so:

  (def foo ((o a 1) (o b 2))) ; pgArc
  (def foo ((= a 1) (= b 2))) ; PyArc
I also plan to support argument-ssyntax, which is basically ssyntax that is only expanded in the argument list. Then you can do this:

  (def foo (a=1 b=2))
This should, of course, be customizable within Arc.

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