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++;
}

[download]
I think you could do that without the macro-magic with simple subs like 
sub my_while(Code &expr, Code &whileblock) {
  while &expr() &whileblock();
}

[download]
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++;
};

[download]
Then, what's the great deal?

rg0now

In reply to Re: Perl 6 and Ruby on Rails by rg0now
in thread Perl 6 and Ruby on Rails by mattr

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