On 03.02.2014, at 16:14, Frank Shearar <frank.shearar at gmail.com> wrote:

> On 3 February 2014 15:06, Tobias Pape <Das.Linux at gmx.de> wrote:
>> On 03.02.2014, at 16:01, Frank Shearar <frank.shearar at gmail.com> wrote:
>> 
>>> On 3 February 2014 14:49, Tobias Pape <Das.Linux at gmx.de> wrote:
>>>> On 03.02.2014, at 15:28, Frank Shearar <frank.shearar at gmail.com> wrote:
>>>> 
>>>>> On 3 February 2014 13:48,  <commits at source.squeak.org> wrote:
>>>>> 
>>>>> So this is a basic depth first traversal with cycle protection, yes?
>>>>> (This pattern seems to crop up _a lot_. Maybe it's worth pulling out
>>>>> as a separate algorithm?)
>>>> 
>>>> Well, there are two such applications:
>>>> One with an explicit down-handling of a variable (like this)
>>>> and one with an implicit variable (semi-global)
>>>>       (Dynamic variable, probably, at least thread-local)
>>>> 
>>>> I would like to have both.
>>>> I propose the (seaside-inspired) #use:during: message for the second.
>>> 
>>> Except that DynamicVariable's #use:during: is incompatible with
>>> stack-slicing, because those kinds of dynamic variables aren't
>>> delimited. (Unlike resumable exceptions, for instance.
>> 
>> Sorry, I (currently) don’t know what you mean by stack-slicing.
>> Are we speaking of Martin von Löwis’ DynamicVariables currently in 4.5/trunk
>> that are based on Thread-local storage
>> or the Seaside ones based on Exceptions?
> 
> Ah! I thought that the Seaside ones were the same the DynamicVariable in trunk!

No; the trunk ones should be better, performance-wise, since they don’t
have to walk the stack on #value

>> (I just see that DV is using #value:during: rather than #use:during:
>> the former is consistent while the latter IMHO speaks better)
> 
> Right. So if Seaside's version uses resumable exceptions, there's no trouble.
> 
> By "stack-slicing" I mean tricks like using delimited continuations.
> Oleg Kiselyov demonstrated [1] how, since there are multiple
> reasonable ways of using delimited control and dynamic bindings
> (trunk's DynamicVariable) together, that there were therefore _no_
> reasonable ways of combining them. Dynamic bindings either capture too
> much or too little of the environment. The answer is to _delimit_ the
> dynamic bindings. Handily, that's exactly what we have with resumable
> exceptions + #on:do:.
> [1] http://www.cs.indiana.edu/~sabry/papers/delim-dyn-bind.pdf

Yes, but I think that is more of concern for continuations than for 
dynamically scoped variables, no? Aren’t those by definition delimitted?

Best
	-Tobias
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