Loop-and-a-half (Re: Curious assignment behaviour)

Michael Abbott michael at rcp.co.uk
Fri Oct 12 09:00:56 CEST 2001


Donn Cave <donn at u.washington.edu> wrote in 
news:9q4it9$tio$1 at nntp6.u.washington.edu:

> I sort of regret wasting bandwidth on this purely academic question,
> but it's a matter of truly venerable tradition that C's loop is a
> bit shy of perfection.  The idea as I understand it, is that there
> are essentially two control points in a loop, the entry, and the
> conditional repeat.  C conflates those two in one, because both
> entry and the conditional repeat have to be at the "top".

Perhaps it's worth recalling at this point the syntax used by Algol68 for a 
loop.  This was really quite pretty and possibly slightly relevant:

    	WHILE
    	    	statements;
    	    	expression
    	DO
    	    	statements
    	OD

Of course, in C this needs to be translated to:

    	while(1)
    	{
    	    	statements;
    	    	if (!expression)  break;
    	    	statements;
    	}

and in Python we have to do exactly the same:

    	while 1:
    	    	statements:
    	    	if not expression:  break
    	    	statements

<Shrug>  It's not pretty, but I'd rather worry about having a conditional 
expression (off topic; we've already beaten that to death and not quite 
managed a PEP out of it...)



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