for / while else doesn't make sense

[Rustom Mody]

On Wednesday, June 15, 2016 at 8:42:33 AM UTC+5:30, Steven D'Aprano wrote:
> On Wed, 15 Jun 2016 01:33 am, Rustom Mody wrote:
> 
> > On Tuesday, June 14, 2016 at 8:13:53 AM UTC+5:30, Steven D'Aprano wrote:
> >> No. The sun exploding was me gently mocking you for your comment
> >> disputing the "unconditional" part. Yes, you are technically right that
> >> technically the "else" block will only run if no "break" is reached, and
> >> no "return" is reached, no exception is raised, also that os._exit or
> >> os.abort aren't called, the CPU doesn't catch fire, and the world isn't
> >> destroyed.
> >> 
> >> If we try to enumerate all the things which could prevent the "else"
> >> block from running, we'll be here for decades. But, and this is the point
> >> that everyone seems to have missed, * every single one of those things*
> >> is completely independent of the for...else statement.
> >> 
> >> *Including* the presence or absence of a "break".
> > 
> > This is real wild:  A break that is inside a for is independent of the
> > for?!?!
> 
> If that's what I said, you would be right to question me. But that's not
> what I said.
> 
> It is legal syntax to have for...else without a break, or a break inside a
> for block with no else. And, if you really want to nitpick, you can even
> have a break statement without a for. (Just stick it inside a while loop
> instead.)
> 
> I know that's it's great fun to pick at nits without making a good faith
> effort to communicate, but honestly Rustom, your following comments do
> suggest that you understood what I was saying.
> 
> 
> [...]
> > This *desire* for what you call isolation is a standard tenet of
> > semantics and is right
> > 
> > It is called compositionality
> > 
> > Inn programming:
> > https://en.wikipedia.org/wiki/Denotational_semantics#Compositionality
> > 
> > More general linguistics:
> > https://en.wikipedia.org/wiki/Principle_of_compositionality
> 
> Thanks for that.
> 
> 
> > However gotos break compositionality unless one introduces heavy artillery
> > like continuations
> > 
> > And break is a euphemism for goto
> 
> Sort of. A break is a jump, and a goto is a jump, but apart from that,
> they're not really the same thing. A goto can jump (almost) anywhere.
> Depending on the language, they can jump into the middle of functions, or
> into the middle of loops. That's what makes them powerful enough to break
> compositionality. But break can only jump to a single place: to the
> statement that follows the for...else compound statement. It's more like a
> return than a goto.

I thought there'd be many examples for showing that break is just goto in disguise... Evidently not

So here is an example in more detail for why/how   break=goto:

http://blog.languager.org/2016/06/break-is-goto-in-disguise.html

[Return/yield are more interesting and complicated...]