I don't have a fix for your actual problem, but The reason it refuses to select the ipv4 is because of longest-token matching. NAME matches a longer token than NUMBER, therefore it always wins.

Update: Change NAME to not accept a dot (and update hostname rule) and then it will work as you originally had: 

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+               separator => DOT

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

    DOT             ~ '.'
    SP              ~ [\s]+
    NAME            ~ [^\s.]+
    NUMBER          ~ [\d]+
END_OF_GRAMMAR

[download]

Good Day,
    Dean

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

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