# PARSE AND EVALUATE LOGICAL EXPRESSIONS WITH A OO PARSE TREE

$::RD_AUTOACTION =
    q{ bless [$item[-1]], $item[0] };

use Parse::RecDescent;

my $parse = Parse::RecDescent->new(<<'EOG');

    expr    :    set | clear | disj
    set    :    'set' atom
    clear    :    'clear' atom
    disj    :    <leftop: conj 'or' conj>
                { bless $item[-1], $item[0] }
    conj    :    <leftop: unary 'and' unary>
                { bless $item[-1], $item[0] }
    unary    :    neg | bracket | atom
    bracket :    '(' expr ')'  { $item[2] }
    neg    :    'not' unary
    atom    :    /[a-z]+/i
EOG

while (<>)
{
    my $tree = $parse->expr($_);
    print $tree->eval(), "\n" if $tree;
}

BEGIN {@var{qw(a c e)} = (1,1,1);}

sub returning
{
      # local $^W;
     # print +(caller(1))[3], " returning ($_[0])\n";
    $_[0];
}

sub expr::eval     { returning $_[0][0]->eval() }
sub disj::eval     { returning join '', map {$_->eval()} @{$_[0]} }
sub conj::eval     { returning ! join '', map {! $_->eval()} @{$_[0]} }
sub unary::eval    { returning $_[0][0]->eval() }
sub neg::eval       { returning ! $_[0][0]->eval() }
sub set::eval      { returning $::var{$_[0][0]->name()} = 1 }
sub clear::eval    { returning $::var{$_[0][0]->name()} = 0 }
sub atom::eval     { returning $::var{$_[0][0]} }
sub atom::name     { returning $_[0][0] }