places where sets are useful

[Doug Moen]

> type
> 	mymodes = (insert, error, append, ...);
> var
> 	status = set of mymodes;
> begin
> ...
> if (status * [insert, append]) <> [] then begin....
> ...
> end
> ...
> end.
> 
> Is much more readable and therefore less likely to get mangled in software
> rewrites then is the exhaustive "if" phrasing.

I agree.  Here's how I would write this in C:

enum {insert, error, append, ... };
#define elem(n) (1 << (int)(n))
short status;
...
	if (status & (elem(insert) | elem(append))) {
		...
	/* add 'error' to set 'status' */
	status |= elem(error);

	/* remove 'error' from set 'status' */
	status &= ~elem(error);