From: mathew <meta@...>
Date: 2005-11-26T00:59:18+09:00
Subject: Re: semenatics of if/unless/while statement modifiers


On Nov 22, 2005, at 12:42 PM, David A. Black wrote:

> On Wed, 23 Nov 2005, mathew wrote:
>>
>> <URL:http://www.rubycentral.com/faq/rubyfaq-6.html>
>>
>> That's a block and a single statement, rather than a loop construct.
>>
>> A real post-test loop would be something like
>>
>> repeat ... until x
>>
>> with no extra do ... end required.
>>
>> And I think that do ... end while x is ugly too. I tend to prefer  
>> doing something to make the loop condition true initially, then  
>> doing a normal while loop.
>>
>
> There's no "do" in the example; it's begin...end.  The "begin" isn't
> "extra" (any more than "repeat" would be), since otherwise you'd have
> no way to know where the body started.
>
> I think it's plenty "real" as is :-)

It's the 'end' that's extra, not the 'do'. I guess I elided too  
much... Let's try again:

do
     x = x + 1
while x < 10

vs

do
    x = x + 1
end while x < 10

The former is a true post-test loop, in that it is a construct like   
if..end  or while..end  that can enclose multiple statements on its  
own. The latter uses a 'do' block to enclose the multiple statements,  
and couples it to a while condition.

And as Matz has just pointed out on this list, the two don't have  
exactly the same semantics, at least as <code> while <cond> is  
implemented today.


mathew