Re: L2R/R2L syntax

[Luke Palmer]

> Date: Mon, 20 Jan 2003 09:20:45 -0800 (PST)
> From: Austin Hastings <[EMAIL PROTECTED]>
> Reply-To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> 
> 
> --- 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?

Oops.  Good point.  In this case I see no way of doing it except for
specifying magic:

  sub elsunless ($test is lazy, &block; &follow) {
    !$test ?? block() :: follow() 
  }

Or something like that.  Darn.

Luke