Where do protocols originate from, I don't know. Maybe Smalltalk. But I first met them in Common Lisp ecosystem.
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https://github.com/franzinc/clim2/blob/master/utils/protocol...
https://github.com/franzinc/clim2/blob/master/clim/stream-de...
https://github.com/dkochmanski/clim-tos/graphs/contributors
Two lessons I learned:
One, Common Lisp code is surprisingly stable over time, with 90% of it still working on CCL/SBCL even though the codebase predates the language standard and is older than I am (don't be mislead by that 1991 on Github, it's much older).
Two, oh my god, trying to understand a large codebase seriously abusing :before/:after/:around methods in large class graphs is not an easy task, though arguably it's more of an issue with available tooling. With better ways to explore runtime program state, it would be much easier to understand and improve such code. I may have written about this last night here: https://mastodon.technology/@temporal/100646861775747986.
Also fun fact, this project is the only case where macroexpanding code crashed my SBCL...
Anyway, let that codebase be and serve as a historical reminder; for more modern implementation of CLIM standard, I'll direct everyone to https://common-lisp.net/project/mcclim/.
I am fascinated, though, by your claim that Lisp also used this term... before reading it I would have been 100% sure that it didn't. I just spent ten minutes trying to find documentation of this, and can't find it... but I am not a native speaker of Lisp and so don't always know where to look; can you point me at a reference? (FWIW, I know of the meta-object protocol, which afaik is a singular thing at a different level of abstraction, and I know about classes and methods and generic functions and mulmethods, which seem like what you are talking about but aren't described by protocol?)