control structures (was "Re: Sins")

[skaller]

Phil Jensen wrote:
 
> I forget if I posted this before, but what I'd like to
> see is the Zahn construct discussed in Knuth's article -
> Pythonically:
> 
>     loop until "element found" or "search failed":
>         ...
>         if blah1 == blah2:
>             "element found"
>         ...
>     when "element found":
>         ...
>     when "search failed":
>         ...

	I've read that article too, and tend to agree.
How about:

	with Found, NotFound:
		initialiser ...
	loop:
		loop body ...
		signal Found ..
	case Found:
		print "found it"
	case NotFound:
		print "couldn't find it"
	finally:
		cleanup ..

Semantics: each label in the 'with' part must be
given as a case. No exit from the loop exists,
except for the listed cases.

Implementation:

	with:
		class Found: pass
		class NotFound: pass
		..
	do:
		try:
			try:
				while 1:
					.. raise Found
			except Found: ...
		finally: ..


> IMHO, "break 3" would be awful.

	Agree. Shades of Tcl. :-(

-- 
John (Max) Skaller, mailto:skaller at maxtal.com.au
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