macros and semicolons

[Chris Dollin]

Mark Hall writes:

   NO macro will work for a swap.  You suffer from the call-by-name rule
   which undid ALGOL in this case.  Consider the expansion of SWAP(i,a[i]):

	   int c; c = i; i = a[i]; a[i] = c;

Disclaimer: I am *not* advocating SWAP macros. But:

    #define SWAP(x, y) \
	{ int *splodge_x = &(x); int *splodge_y = &(y); 
	int splodge_t = *splodge_x; \ 
	*splodge_x = *splodge_y; *splodge_y = splodge_t; }

does not suffer from the call-by-name problem (Algol 60 did not have
call-by-reference, but Algol 68 does (in a manner of speaking). Hence Mark's
criticism fails.

However, the amount of effort required to write even a specialised swap macro
should have suggested by now [anyone who hasn't, go read the FAQ] that swap
macros are dead ducks. 

Dead, you hear me? D - E - D, DEAD.

We now return you to your regular sniping about the NULL pointer.
--

Regards, Chris ``GC's should take less than 0.1 second'' Dollin.