Hmm. Perhaps this should supersede the procedural interface rather than supplementing it?
On Tue, Feb 4, 2025, 5:08 AM Daphne Preston-Kendal <d...@nonceword.org> wrote: > We’ve talked elsewhere about convenience syntax for this before, but I > think I now have worked out reasonable syntax for it. > > SRFI 254 should add syntax called ephemeron-case: > > (ephemeron-case <<expression>> > ((<<key identifier>> . <<value identifier>>) > <<body>>) > (else <<body>>)) > > > Semantics: > > The <<expression>> is evaluated to produce an ephemeron. > > If the ephemeron is live, the first <<body>> is evaluated with the > identifiers <<key identifier>> and <<value identifier>> in scope. The <<key > identifier>> is bound as if to identifier syntax which both returns the key > of the ephemeron and ensures that it is kept live, as if by the > reference-barrier procedure. It is a syntax violation to use set! on the > <<key identifier>>. The <<value identifier>> is bound as a variable to the > value of the ephemeron. > > If the ephemeron is broken, the second <<body>> is evaluated with no > additional identifiers in scope. > > The advantage is that with convenience syntax available which > automatically does all the right things, people will be less tempted to do > broken things like first checking the liveness of an ephemeron before > pulling out the key and value, or forgetting to use reference-barrier. > > > Daphne > >
