# PARSE LOGICAL EXPRESSIONS

$RD::TRACE=1;

use Parse::RecDescent;

$grammar =
q{
    expr    :    disj  no_garbage

    no_garbage: /^\s*$/
          | <error: Trailing garbage>

    disj    :    conj  ('or' conj)(s?)

    conj    :    unary ('and' unary)(s?)

    unary    :    'not' atom
        |    '(' disj ( ')' | <error> )
        |    atom

    atom    :    /<.+?>/

};

$parse = new Parse::RecDescent ($grammar);

$input = '';

print "> ";
while (<>)
{

    if (/^\.$/) { defined $parse->expr($input) or print "huh?\n"; $input = '' }
    else        { chomp; $input .= " $_" }
    print "> ";
}