Re: [wxperl-users] declarative syntax

[Sergei S. <ser...@ya...>]

--- Eric Wilhelm <scr...@gm...> wrote:

> # from Sergei Steshenko
> # on Saturday 17 March 2007 07:16 pm:
> 
> >I am not sure I clearly understand what it's about, but why new
> > syntax/language to describe hierarchical relationship if Perl already
> > supports hierarchical data structures ?
> 
> One word:  concisification
> 
> >my $children_array_ref = # or should it be hash ref ?
> 
> No, order matters.
> 
> >  [
> >    { # first child
> 
> oops, we lost the order now
> 
> >    custom_bit =>
> >      {
> ...
> >    text_ctrl =>
> >      {
> >      type => 'ctrl',
> >      label => "", # I'm not sure about this
> >      style =>
> >        {
> >        te => MULTILINE|READONLY|DONTWRAP 
> >        # these are meant to be bitwise OR'ed constants 
> >        } 
> 
> Yeah, but the te => 'string|string|string' means the style() function 
> can append wxTE_ to the front, so-as to Wx->"wxTE_$thing" it.
> 
> >      }
> >    },
> >
> >    { # second child
> >    ...
> >    }
> >  ];
> 
> >Whenever I see another language inside Perl, I'm getting really
> > nervous - another (possibly incomplete) definition, another (possibly
> > buggy) parser ...
> 
> Nope, no parser.
> 
> >Well, the original example is likely still Perl, but why a subroutine
> > where plain hierarchical data structure should suffice ?
> 
> The data structure would basically have to be array refs all the way 
> down.  Also, the style() function does some mapping.  The idea was 
> basically to make a mini-language that would add some unverbosity and 
> other conveniencification.
> 
> (The Bushism-ated words are jokes.  You should laugh now.  I'm not 
> really going to extendify the language like that.)
> 
> A sufficiently expressive data-structure would be good, but it wouldn't 
> be declarative.  The benefit of the declarative bits of code is that 
> their procedural guts can remove the need for ']]]]]]]]]]'(did I get 
> enough brackets in there?)-ish stuff.  I'm still on the fence about 
> many details of implementing either or both.
> 
> --Eric
> -- 
> software:  a hypothetical exercise which happens to compile.

I don't quite understand the ']]]]]]]]]]' part - do you think that nested
function calls are any better ?

The point of Perl data structures is that is is also (and primarily) code.

I.e. suppose you need to write something like this:

{
...
funky_array => [1, 2, 3, 5, 8 ...], # element is the some of previous two, and this way
                                    # 100 times; 
...
}
.

So, this is Perl, and there is more than one to do it, and I would do it
this way:

{
...
funky_array => do{
                 my @tmp_array;  # no name clash danger, the scope
                                 #  protects from name contention

                 my $number_of_times = 100; # I said 100 times, dodn't I ?

                 my $previous_element = 0;
                 my $element = 1;

                 while($number_of_times-- > 0)
                   {
                   $element += $previous_element;
                   push @tmp_array, $element;
                   $previous_element = $element;
                   }

                 \@tmp_array; # the array reference to be returned
                 }
};

So, the point of this example is that there should be canonical/normalized data
structure and there can be infinite number of ways to produce it.

IMO the power of Perl is anonymity - this ensures no name clashes, and the 'do'
statement is an anonymous executable/executed code block returning a value
(array reference in this case).

Define the canonical form and give user freedom to produce it - this is how
I'm writing my stuff.

...

FWIW, have a look at

http://exit1.org/Gtk2-Ex-FormFactory/

- though this is for gtk2-perl, the idea is still OK IMO.

Regards,
  Sergei.



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