Feature request: extending comma operator's functionality

[H. S. Teoh]

On Fri, Oct 05, 2012 at 05:23:40PM +0200, Don Clugston wrote:
[...]
> My feeling is that  do{}while() is a fairly useless concept, and
> this is part of the reason.
> In my experience genuine do-while loops are extremely rare, and it
> only takes a slight change to the loop to force a different
> structure to be used.
> Conditional loops which don't follow the while(){...} pattern
> normally follow the loop-and-a-half pattern, also known as
> begin-while-repeat (I think that's the name Knuth used). I'll call
> it 'super do':
> 
> super do {
>    foo();
>    while(cond);
>    bar();
> }
> 
> which in D is better modelled by:
> 
> for (;;)
> {
>    foo();
>    if (!cond) break;
>    bar();
> }

This isn't "super do", it's just "loop", the way nature intended. ;-)
I've always been an advocate of this construct:

	loop {
		// initial part of loop body
	} while(cond) {	// exit point
		// trailing part of loop body
	}

To some extent, D (and C/C++)'s for-loops exhibit a similar structure:

	for (X; Y; Z) {}

The trailing part of the loop body corresponds with Z; the condition
corresponds with Y.

To avoid the introduction of a new keyword, we may fuse the do-loop and
the while-loop together:

	do {
		...
	} while (cond) {
		...
	}

The current do-loop is simply a special case of this construct where the
second {...} is replaced with a ;, and the while-loop is a special case
of this construct where the initial part of the loop is elided.

I argue that this generalized construct is much more useful than the
do-loop or while-loop individually, plus it doesn't break any existing
code.


T

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