Re: L2R/R2L syntax

[Austin Hastings]

--- Luke Palmer <[EMAIL PROTECTED]> wrote:
> > Mailing-List: contact [EMAIL PROTECTED]; run by ezmlm
> > Date: Sat, 18 Jan 2003 15:07:56 -0800 (PST)
> > From: "Sean O'Rourke" <[EMAIL PROTECTED]>
> > Cc: Damian Conway <[EMAIL PROTECTED]>,
> >     "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
> > X-SMTPD: qpsmtpd/0.20, http://develooper.com/code/qpsmtpd/
> > 
> > On Sat, 18 Jan 2003, Michael Lazzaro wrote:
> > > So 'if' and friends are just (native) subroutines with prototypes
> like:
> > >
> > >    sub if (bool $c, Code $if_block) {...};
> > 
> > IIRC it's not that pretty, unfortunately, if you want to support
> this:
> > 
> >     if $test1 {
> >     # blah
> >     } elsunless $test2 {
> >     # ...
> >     }
> 
> Ahh, you used the unmentionable _correctly_, unlike so many who
> misunderstood some six months ago.
> 
> > since that gets parsed as
> > 
> >     if($test1, { ... }) # aiee: too many arguments to "if"
> 
> That is not a problem:
> 
>   # We'll just pretend that dereferencing the "undef" sub does
> nothing
> 
>   sub if ($test, &block; &follow) {
>     # ... er, how do you write "if"? Hmm...
>     $test ?? block() :: follow()
>   }
> 
>   sub elsunless ($test, &block; &follow) {
>     !$test ?? block() :: follow() 
>   }
> 
> So:
> 
>   if $test1 { 
>     # stuff
>   }
>   elsunless $test2 {
>     # stuff 2
>   }
> 
> Becomes (semantically):
> 
>   if($test1, {
>     # stuff
>   }, elsunless($test2, {
>     # stuff 2
>   }));

Is this magic, or do coderef args construct closures, or what? How do
you avoid evaluating the argument to elsunless() when feeding it to the
if() sub?

=Austin