Perl Style: Avoid Byte Processing

C programmers often try to process strings a byte at a time. Don't do that! Perl makes it easy to take data in big bites.
Don't use getc. Grab the whole line and operate on it all at once.

Even operations traditionally done a char at a time in C, like lexing, should be done differently. For example:

    @chars = split //, $input;
    while (@chars) {
      $c = shift @chars;
      # State machine;
    }

Is far too low level. Try something more like:

    sub parse_expr {
	local $_ = shift;
	my @tokens = ();
	my $paren = 0;
	my $want_term = 1;

	while (length) {
	    s/^\s*//;

	    if (s/^\(//) {
		return unless $want_term;
		push @tokens, '(';
		$paren++;
		$want_term = 1;
		next;
	    }

	    if (s/^\)//) {
		return if $want_term;
		push @tokens, ')';
		if ($paren < 1) {
		    return;
		} 
		--$paren;
		$want_term = 0;
		next;
	    }

	    if (s/^and\b//i || s/^&&?//) {
		return if $want_term;
		push @tokens, '&';
		$want_term = 1;
		next;
	    }

	    if (s/^or\b//i || s/^\|\|?//) {
		return if $want_term;
		push @tokens, '|';
		$want_term = 1;
		next;
	    }

	    if (s/^not\b//i || s/^~// || s/^!//) {
		return unless $want_term;
		push @tokens, '~';
		$want_term = 1;
		next;
	    }

	    if (s/^(\w+)//) {
		push @tokens, '&' unless $want_term;
		push @tokens, $1 . '()';
		$want_term = 0;
		next;
	    }

	    return;

	}
	return "@tokens";
    }