Re: Perl 6 and Ruby on Rails

[rg0now]

Here is my strike at "Passing code blocks around as macros":

macro statement_control:<my_while>($expr, &whileblock) {
  while $expr &whileblock();
# do we need while $expr do &whileblock();    ?
}

my $i = 0;
my_while {$i < 10} {
  say "i: $i";
  my $j = 0;
  my_while {$j < 10} {
    say "j: $j";
    $j++;
  }
  $i++;
}

I think you could do that without the macro-magic with simple subs like

sub my_while(Code &expr, Code &whileblock) {
  while &expr() &whileblock();
}

This is because (from S4):

Every block is a closure. (That is, in the abstract, they're all anonymous subroutines that take a snapshot of their lexical scope.) How any block is invoked and how its results are used is a matter of context, but closures all work the same on the inside.

Digging around the Perl 6 specs, I begin to see that perhaps S4 holds some of the nicest things in the design of Perl 6. And, quite frankly, the more I read the more I feel how much I miss a working Perl 6 compiler...

Update: hey, we can, with a slightly more convoluted syntax, do this with Perl 5 too:

use strict;
use warnings;

sub my_while(&&){
  my($expr, $whileblock) = @_;
  while(&$expr()){
    &$whileblock();
  }
}

my $i = 0;
my_while sub {$i < 10}, sub {
  print "i: $i\n";
  my $j = 0;
  my_while sub {$j < 10}, sub {
    print "j: $j\n";
    $j++;
  };
  $i++;
};

Then, what's the great deal?

[duff]

the more I read the more I feel how much I miss a working Perl 6 compiler

What's pugs? Chopped liver? :-)

[rg0now]

Now guess what! I managed to make the damned thing work in Pugs! Here is the slightly modified version that compiles and runs with current Pugs:

use v6;

sub my_while(Code $expr, Code $whileblock) {
  while ($expr()) { $whileblock() };
}

my $i = 0;
my_while {$i < 10}, {
  say "i: $i";
  my $j = 0;
  my_while {$j < 10}, {
    say "j: $j";
    $j++;
  };
  $i++;
};

What really surprized me was the fact that Pugs appears to do the right thing on closing closures, which I did not think should work right now. Also, do not really expect Pugs to verify whether my_while is called with actual blocks or not, because it does not work. Moreover, it is astonishingly slow. But I keep on loving it...:-)

[dragonchild]

hey, we can, with a slightly mlre convoluted syntax, do this with Perl 5 too:

That's how Error works, and it has memory-leak issues. :-)

[jdporter]

It doesn't need to be quite as bad as that... though still, bad enough:

my_while { $i < 10 } sub {
  print "i: $i\n";
  my $j = 0;
  my_while { $j < 10 } sub {
    print "j: $j\n";
    $j++;
  };
  $i++;
};

[mattr]

Hmm. Definitely I will do some more reading. Thanks for the experimentation.

I was thinking about a way to state business rules for a system I'm building now, but to be honest I always wondered when we would get to the point that programming looked more like talking to the "Smart Girl" spaceship Gay Deceiver in Robert A. Heinlein's The Number of the Beast. Between Cyc and Perl6 we seem to be getting closer..

"Program, Gay. Add running news retrieval. Area, Arizona Strip north of Grand Canyon plus Utah . Persons: all persons listed in current running news retrieval programs plus rangers, Federal rangers, forest rangers, park rangers, state rangers. End of added program."

The above story uses a verbally programmed autopilot a bit smarter than what we have now, but English constructs like verb-object-prepositional_phrase-conditional_clause might be possible with Perl 6.. Anyway thank you very much and I will certainly do some more reading on it.