Re: Iterating elements at different level

[choroba]

Discipulus teased me to try solving the problem using the Marpa parser. It took me a lot more time than I had thought: I didn't find a way how to retrieve the "depth" in a parse tree in order to multiply by it. You can attach 0 as the depth to each number, though, and increment it on each its inclusion into a list:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use Marpa::R2;
use List::Util qw{ sum };

my $dsl = << '__DSL__';

lexeme default = latm => 1
:default ::= action => ::first

Top   ::= List                                   action => resolve
List  ::= ('{') Terms ('}')
Terms ::= Term+              separator => comma  action => include
Term  ::= num                                    action => create
        | List

num   ~ [0-9]+
comma ~ ','

__DSL__

sub create  { [ [ $_[1], 0 ] ] }
sub include { shift; [ map { map [$_->[0], 1 + $_->[1]], @$_ } @_ ] } 
+ # do you still love me?
sub resolve { shift; sum map $_->[0] * $_->[1], @{ $_[0] } }

my $grammar = 'Marpa::R2::Scanless::G'->new({ source => \$dsl });

my @strings = ( '{{1,1},2,{1,1}}',                       # the functio
+n should return 10
                '{1,{4,{6}}}',                           # the functio
+n should return 27
                '{{1,1,1,1},{1,1,{2,2}},{1,{2,{3,3}}}}'  # Buk 56
              );

for my $s (@strings) {
    my $v = $grammar->parse(\$s, 'main');
    say $$v;
}