Invoking return through a function?

[Alberto Riva]

On 10/30/2017 10:27 AM, Rhodri James wrote:
> On 29/10/17 16:45, Alberto Riva wrote:
>> On 10/29/2017 11:13 AM, bartc wrote:
>>>
>>> (What the OP wants was also proposed a few weeks back in comp.lang.c. 
>>> But that was only within nested functions, so if H is inside G, and G 
>>> is inside F, then a 'returnall' from H would return directly directly 
>>> from F. Apparently Lisp allows this...)
>>
>> Well, not directly, but it can be simulated with the condition system 
>> (equivalent to try/except) or with throw/catch, which is similar but 
>> doesn't use exceptions.
>>
>> But my point was that in Lisp you don't need to do this, because you 
>> can write a macro that expands into a return *in place*, without 
>> calling a separate function, and this eliminates the problem entirely. 
>> Since Python doesn't have macros I was looking for the next-best 
>> solution, but there doesn't seem to be one. Oh, well...
> 
> You can do the same in C.  I've had the displeasure of trying to 
> maintain such code.  It was near-unreadable, because it constantly broke 
> your expectations of what the code flow *could* be.  The fact that 
> something that could return from the middle of your function without the 
> slightest indication was a rich source of bugs.

Just curious: how is this different from calling a function that throws 
an exception (that may or may not be caught by some other function 
higher up in the call stack)? That also breaks your expectations of what 
the code flow would be...

To clarify, I agree with your concern. What I mean is that even in 
normal conditions there's never any guarantee that the code flow is what 
you expect it to be just by reading the body of a function. The kind of 
statement I was trying to add would at least have made that explicit: 
return-if-so-and-so-happens.

Alberto



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