On 31 March 2010 20:21, Jonathan S. Shapiro <[email protected]> wrote:
> On Tue, Mar 30, 2010 at 7:02 AM, Michal Suchanek <[email protected]> wrote:
>>
>> You mean the C
>>
>> while() {}
>> {} while();
>>
>> loops?
>
> Actually, I meant "while() {}" and "do {} while ()", but yes. :-)
>
>> I would expect that for(;;) would not be needed when constructs like
>> foreach or map are available so you can just have a syntax which
>> allows the condition to be at the beginning or the end like
>
> for(;;) isn't a big concern. It's mere syntactic sugar on "do {} while
> ()". If adding this syntactic sugar helps programmers migrate, it's
> probably useful.
>
> The mildly subtle problem is the result type of the loop construct.
> Because the "do {} while()" form executes at least once, we can
> declare that the value of the loop is the value of the last statement
> executed within the body (I'm ignoring explicit "break" for this
> discussion, but we can extend to that easily).
>
> Unfortunately, the "while() {}" form may *not* execute even once, and
> so we cannot determine the type of the value. This is like the
> difference between
>
> if () then e1 else e2
> if () then e1
>
> In BitC, we chose to resolve this by deciding that a missing else
> clause was treated as "else Unit". That is: a one-legged if must
> return unit. I suppose that we could do the same thing with the
> "while() {}" form. Would that strike people as weird?
If they use a while {} as part of an expression then it should not.
It's the same semantic as if () {} and it really is a the same thing.
Thanks
Michal
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