PS I found Oleg's explanation of why a primitive ‘dynamic-wind’ should
have no role in a language with delimited continuations:
https://okmij.org/ftp/continuations/implementations.html#dynamic-wind

Am Do., 1. Jan. 2026 um 13:48 Uhr schrieb Marc Nieper-Wißkirchen
<xxxxxx@gmail.com>:
>
> Hi!
>
> Thanks for the question.
>
> The model of SRFI 248 (which is deliberately simple and basic but rich
> enough to build more complex abstractions on top of it) is that there
> is basically just one type of effect. Whatever effect is raised, the
> innermost handler is called (and can move control to the next
> enclosing handler by reraising the effect), so one can detect every
> unwinding of the stack through
> ‘with-unwind-handler’/‘raise-continuable’ and thus implement a version
> of ‘dynamic-wind’ that works for delimited continuations.
>
> With delimited continuations, ‘call/cc’ is not really necessary any
> more (except for backward compatibility). As the unwinding occurring
> from instantiating a continuation K captured by ‘call/cc´ does not
> trigger any unwind handler, one still needs the legacy ‘dynamic/wind’
> as long as the legacy ‘call/cc’ exists. One could amend SRFI 248 by
> integrating ‘call/cc’ fully by demanding that instantiating K raises a
> condition object, which leads to triggering the unwind handlers. This
> is less conservative but probably The Right Thing.
>
> Marc
>
> Am Do., 1. Jan. 2026 um 04:24 Uhr schrieb Eleanor Bartle
> <xxxxxx@eleanor-nb.com>:
> >
> > Apologies for the noise. I’m a passive nerd, attempting to understand Scheme internals, enamoured by delimited continuations.
> >
> > One thing I don’t understand in this SRFI is how it would be able to dispense with dynamic-wind, were it not for call/cc. How does that come about? More precisely, why does the unwinding/rewinding of a delimited continuation not necessitate dynamic-wind, and why does that reason not apply to call/cc?
> >
> > Eleanor