Almost all of them have something like that: Robert Strandh has a technique that looks promising[1] and is being implemented as a library, I believe. CLOS’s cus

Almost all of them have something like that: Robert Strandh has a technique that looks promising[1] and is being implemented as a library, I believe. CLOS’s customization hooks allow you to switch out the implementation of “generic function” on a case-by-case basis which can be used to implement this sort of optimization. [1]: http://metamodular.com/SICL/generic-dispatch.pdf http://metamodular.com/SICL/generic-dispatch.pdf