Back in July 2020, Mark Weaver wrote:

Also, the provided implementations of 'generator-find', 'generator-any'
and 'generator-every' are incorrect:

Shiro Kawai has now fixed these bugs, and they have been merged into SRFI 121. Note that even if it doesn't become part of Guile's batteries-included, the code should still work on Guile as an R6RS library. However, the upward compatible SRFI 158 provides more generator function as well as support for accumulators, the dual of generators.

Mark: I'm interested to know if you have a sketch of ideas for a more efficient implementation of SRFI 121/158. You say it requires specific knowledge of Guile internals, but are you willing to sketch how you might do it? Thanks.