I have a Marpa::R2 parser that is attempting to differentiate between IP addresses and hostnames without a difference in leading keywords. The actual grammar I am using is complicated enough not to try and replicate it here, but a minimally-reproducable example of the same problem is below:

#!/usr/bin/env perl
use warnings;
use strict;

use Data::Dumper;
use Term::ANSIColor qw(:constants);
use Marpa::R2;

my $rules = <<'END_OF_GRAMMAR';
    lexeme default  = latm => 1
    :default        ::= action => [name,values]
    :start          ::= <entry>

    <entry>         ::= <op> (SP) <hostaddr4>
    <op>            ::= 'add' | 'remove'
    
    <ipv4>          ::= NUMBER ('.') NUMBER ('.') NUMBER ('.') NUMBER
    <hostname>      ::= NAME
    
    <hostaddr4>     ::= <ipv4> | <hostname>
    
    SP              ~ [\s]+    
    NAME            ~ [\S]+
    NUMBER          ~ [\d]+
END_OF_GRAMMAR

my $input = <<'END_OF_INPUT';
add 192.0.2.1
add www.example.org
remove 192.0.2.2
END_OF_INPUT

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

for (split /^/m, $input) {
    chomp;
    if (length $_) {
        print "\n\n$_\n";
        
        my $recce = Marpa::R2::Scanless::R->new({
            grammar => $grammar, 
            ranking_method => 'rule'
        });
        
        eval { $recce->read(\$_ ) };
        print ($@ ? (RED . "$@\n") : GREEN);
        print $recce->show_progress(), "\n";
        print Dumper($recce->value), "\n\n", RESET;
    }
}

[download]

From what I can tell, Marpa always picks the <hostname> form of the grammar, even on lines that look more like IPs. I assume this is because the character class [\S]+ also includes the characters which make up an IP address.

So far, in my grammar definition, I've tried:

<hostaddr4>     ::= <ipv4> | <hostname>

<hostaddr4>     ::= <ipv4> || <hostname>

<hostaddr4>     ::= <hostname> | <ipv4>

<hostaddr4>     ::= <hostname> || <ipv4>

<hostaddr4>     ::= <ipv4>      rank => 2
                  | <hostname>  rank => 1


<hostaddr4>     ::= <ipv4>      rank => 1
                  | <hostname>  rank => 2


<hostaddr4>     ::= <ipv4>      rank => 1
<hostaddr4>     ::= <hostname>  rank => 2

<hostaddr4>     ::= <hostname>  rank => 1
<hostaddr4>     ::= <ipv4>      rank => 2

[download]

...and none seem to make a difference. They all yield the ['hostname', '192.0.2.1'] array.

The only thing that does it is removing the <hostname> alternate from <hostaddr4> (which does not match the grammar of the data I am parsing), and then the representation changes to ['ipv4', '192', '0', '2', '1']

Can anyone advise the correct approach in this (seemingly) simple case?

J.

In reply to Cannot get Marpa::R2 to prioritise one rule over another by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.