I mentioned Brad Cox's "software ICs" today on the phone in a conversation about big ideas in programming, not knowing that he'd passed away a couple weeks ago.
Here's the Objective-C paper at last year's HOPL:
"The origins of Objective-C at PPI/Stepstone and its evolution at NeXT"
That's a truly excellent paper (and exceptionally honest, considering some of the touchy subjects involved) and disentangles many of the origins of the various concepts in Objective C between the Stepstone and NeXT environments.
Here's the Objective-C paper at last year's HOPL:
"The origins of Objective-C at PPI/Stepstone and its evolution at NeXT"
https://dl.acm.org/doi/10.1145/3386332
https://news.ycombinator.com/item?id=23516334