http://stackoverflow.com/questions/26173372/parsing-an-ad-hoc-tree/26192035

highly-ambiguous.pl

use 5.010;
use strict;
use warnings;

use Data::Dumper;
$Data::Dumper::Indent = 0;
$Data::Dumper::Terse = 1;
$Data::Dumper::Deepcopy = 1;

use Marpa::R2;

my $g = Marpa::R2::Scanless::G->new( { source => \(<<'END_OF_SOURCE'),

    :default ::= action => [ name, value ]
    lexeme default = action => [ name, value ] latm => 1

        data    ::= heading tables

        heading ::= string
        tables  ::= table+

        table ::= row+
        row   ::= level name ':' value

        level ~ '+' | '++' | '+++' | '++++'
        name  ::= string
        value ::= number
        value ::= string
        value ::=

        string ~ [\w\& ]+
        number ~ [\d]+

    :discard ~ whitespace
    whitespace ~ [\s]+

END_OF_SOURCE
} );

my $input = <<EOI;
Soccer

+Team:US
++Shirt:Red & White Stripes
++Shorts:Blue
++Players:17
+++Active:11
++++Forward:2
++++Midfield:4
++++Defense:4
++++Goalkeeper:1
+++Substitute:6
++++Forward:1
++++Midfied:2
++++Defense:3
++++Goalkeeper:

+Team:Mexico
++Shirt:Green
++Shorts:White
++Players:17
+++Active:11
++++Forward:3
++++Midfield:3
++++Defense:4
++++Goalkeeper:1
+++Substitute:6
++++Forward:2
++++Midfield:1
++++Defense:2
++++Goalkeeper:1
EOI

my $r = Marpa::R2::Scanless::R->new( {
    max_parses => 10000,
    grammar => $g,
    trace_terminals => 0,
    trace_values => 0,
} );
eval {$r->read(\$input)} || warn "# Parse failure, progress report is:\n" . $r->show_progress;

# nearly endless without max_parses
while ( defined( my $value_ref = $r->value() ) ) {
    warn Dumper ${ $value_ref };
}