sub Calc {
    local($_) = @_;
    local @v = ();
    eval { 
        expr();
        /\G\s*\z/gcx or err( 'incomplete' );
    } or err( $@ );
    return @v;
}

while( <> ) {
    s/[\r\n]*//g; ## "chomp"
    print $_," = ", Calc($_), "\n"; 
}