PDD 03 Issue: keyword arguments

[Sam Ruby]

Python provides the ability for any function to be called with either 
positional or keyword [1] arguments.  Here is a particularly brutal example:

args={'a':1,'b':2,'c':3}
def f(a,b,c): return (a,b,c)
def g(b,c,a): return (a,b,c)
for j in [f,g]: print j(1,2,3)
for j in [f,g]: print j(a=1,b=2,c=3)
for j in [f,g]: print j(*args.values())
for j in [f,g]: print j(**args)
I see nothing in pdd 03 that provides any guidance as to how to handle 
this.  What makes this issue so critical is that any solution will 
potentially affect *every* function.

- Sam Ruby
P.S. Jython handles the above test correctly.  Iron-Python handles all 
but the **args properly.

[1] http://docs.python.org/ref/calls.html

Keyword arguments

[Piers Cawley]

So, I was, thinking about the way Common Lisp handles keyword
arguments. It's possible to declare a Lisp function as follows:

(defun make-para ( content key alignment font size color ) ...)

The point here is that the first argument is dealt with positionally,
and subsequent, optional args are dealth with as keyword arguments. It
seems to me that similar functionality might sit well with Perl 6, but
I'm not sure I can think of a good declaration syntax. Calling syntax
is easy:

make_para $text, font = 'Helvetica,Arial,Whatever';

Any thoughts?

-- 
Piers

   It is a truth universally acknowledged that a language in
possession of a rich syntax must be in need of a rewrite.
 -- Jane Austen?

Re: Keyword arguments

[Austin Hastings]

I think Damian already covered this: it's the semicolon.

sub mysub(String $content; int $key, int $align)
{
 ...
}

sub callmysub
{
  mysub(Testing .. 1, 2, 3!; key = 1024, align = Module::RIGHT);
}

Which, upon reflection, apparently introduces an implicit hashparsing
context for autoquoting hashkeys.

=Austin

--- Piers Cawley [EMAIL PROTECTED] wrote:
 So, I was, thinking about the way Common Lisp handles keyword
 arguments. It's possible to declare a Lisp function as follows:
 
 (defun make-para ( content key alignment font size color ) ...)
 
 The point here is that the first argument is dealt with positionally,
 and subsequent, optional args are dealth with as keyword arguments.
 It
 seems to me that similar functionality might sit well with Perl 6,
 but
 I'm not sure I can think of a good declaration syntax. Calling syntax
 is easy:
 
 make_para $text, font = 'Helvetica,Arial,Whatever';
 
 Any thoughts?
 
 -- 
 Piers
 
It is a truth universally acknowledged that a language in
 possession of a rich syntax must be in need of a rewrite.
  -- Jane Austen?


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Re: Keyword arguments

[Luke Palmer]

 Mailing-List: contact [EMAIL PROTECTED]; run by ezmlm
 From: Piers Cawley [EMAIL PROTECTED]
 Date: Wed, 06 Nov 2002 12:44:39 +
 X-SMTPD: qpsmtpd/0.12, http://develooper.com/code/qpsmtpd/
 
 So, I was, thinking about the way Common Lisp handles keyword
 arguments. It's possible to declare a Lisp function as follows:
 
 (defun make-para ( content key alignment font size color ) ...)
 
 The point here is that the first argument is dealt with positionally,
 and subsequent, optional args are dealth with as keyword arguments. It
 seems to me that similar functionality might sit well with Perl 6, but
 I'm not sure I can think of a good declaration syntax. Calling syntax
 is easy:
 
 make_para $text, font = 'Helvetica,Arial,Whatever';
 
 Any thoughts?

Sure.  It already does that.  But only if the caller feels like it.
If you can remember the order of all those arguments, great, but if
you can't, you can use keywords.

sub make_para($text; $alignment, $font, $size, $color) {...}

Can be called in a lot of ways, one of which you wrote above.

I sure hope it doesn't complain that you didn't specify alignment.  I
guess that's what exists() is for.

Luke

Re: Keyword arguments

[Paul Johnson]

Austin Hastings said:

 sub callmysub
 {
   mysub(Testing .. 1, 2, 3!; key = 1024, align = Module::RIGHT);
 }

 Which, upon reflection, apparently introduces an implicit hashparsing
 context for autoquoting hashkeys.

Those are pairs, aren't they?

-- 
Paul Johnson - [EMAIL PROTECTED]
http://www.pjcj.net

Re: Keyword arguments

[Piers Cawley]

Paul Johnson [EMAIL PROTECTED] writes:

 Austin Hastings said:

 sub callmysub
 {
   mysub(Testing .. 1, 2, 3!; key = 1024, align = Module::RIGHT);
 }

 Which, upon reflection, apparently introduces an implicit hashparsing
 context for autoquoting hashkeys.

 Those are pairs, aren't they?

Yup.

-- 
Piers

   It is a truth universally acknowledged that a language in
possession of a rich syntax must be in need of a rewrite.
 -- Jane Austen?