DCONWAY / Parse-RecDescent-1.96.0 / demo / demo_delete.pl 

            

              
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#! /usr/local/bin/perl -sw
# DELETABLE PRODUCTIONS
use Parse::RecDescent;
$grammar =
q{
        commands :      command(s)
        command  :      directive
                 |      evaluation
        directive:      'only prefix'
                            { $thisparser->{deleted} = {infix=>1,postfix=>1} }
                 |      'not prefix'
                            { $thisparser->{deleted}{prefix} = 1 }
        evaluation:     <reject: $thisparser->{deleted}{prefix}> op var var
                                { print "prefix $item[3] $item[2] $item[4]\n" }
                  |     <reject: $thisparser->{deleted}{infix}> var op var
                                { print "infix $item[2] $item[3] $item[4]\n" }
                  |     <reject: $thisparser->{deleted}{postfix}> var var op
                                { print "postfix $item[2] $item[4] $item[3]\n" }
        op        :     '+' | '-'
        var       :     /(?!\d)\w+/
};
$parse = new Parse::RecDescent ($grammar);
while (<DATA>)
{
        $parse->commands($_);
}
__DATA__
a + b
+ a b
a b +
not prefix
a + b
+ a b
a b +
only prefix
a + b
+ a b
a b +
not prefix
a + b
+ a b
a b +