[Python-Dev] Re: anonymous blocks

Phillip J. Eby pje at telecommunity.com
Mon Apr 25 05:57:37 CEST 2005

At 11:39 PM 4/24/05 -0400, Bob Ippolito wrote:

>On Apr 24, 2005, at 11:32 PM, Phillip J. Eby wrote:
>>At 04:57 PM 4/24/05 -0700, Guido van Rossum wrote:
>>>So a block could return a value to the generator using a return
>>>statement; the generator can catch this by catching ReturnFlow.
>>>(Syntactic sugar could be "VAR = yield ..." like in Ruby.)
>>[uncontrolled drooling, followed by much rejoicing]
>>If this were available to generators in general, you could untwist 
>>Twisted.  I'm basically simulating this sort of exception/value passing 
>>in peak.events to do exactly that, except I have to do:
>>     yield somethingBlocking(); result=events.resume()
>>where events.resume() magically receives a value or exception from 
>>outside the generator and either returns or raises it.  If 
>>next()-with-argument and next_ex() are available normally on generators, 
>>this would allow you to simulate co-routines without the events.resume() 
>>magic; the above would simply read:
>>     result = yield somethingBlocking()
>>The rest of the peak.events coroutine simulation would remain around to 
>>manage the generator stack and scheduling, but the syntax would be 
>>cleaner and the operation of it entirely unmagical.
>Only if "result = yield somethingBlocking()" could also raise an exception.

Read Guido's post again; he proposed that passing a result would occur by 
raising a ReturnFlow exception!  In other words, it's the result passing 
that's the exceptional exception, while returning an exception is 
unexceptional.  :)

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