Some of those ideas are also in OOP. But I think that might just be seeing what you are used to. The paper's ideas fit eg OCaml's ideas of modules and abstract types just as well.
A key difference from OCaml's modules (besides the lack of type parameterization) is Liskov's data types have associated data. So it's more like Rust's structs. Also, like in Rust, there is no support for multiple implementations of a single signature.
Though couldn't you associate data with your OCaml modules, too?
It's been a while since I played with OCaml, but I'm pretty sure that modules are stateless. A quick googling shows that you can use global state, but it's not the same as one instance of state per one instance of struct as in Rust.
I should have been less tentative: you can add values to modules, and you can add mutable values to modules. And that state is not global at all. (Though you might be able to ask for global state.)
They are often used without mutable state, but the language doesn't make them so.
See eg https://realworldocaml.org/v1/en/html/first-class-modules.ht...
Then you were right, I should've checked before answering.
No worries. Thanks!
I just have the feeling that the author is trying to explain OOP with the vocabulary of 1974.
What did you find interesting in this paper?
Maybe you are referring to some material from the opening like:
> The programmer is initially concerned with
satisfying himself (or proving) that his program
correctly solves the problem. In this analysis he
is concerned with the way his program makes use of
the abstractions, but not with any details of how
those abstractions may be realized. When he is
satisfied with the correctness of his program, he
turns his attention to the abstractions it uses.
I can imagine how to a modern reader the usage of the male pronoun here might sound excessive, but I think it's useful to note that this would be standard academic writing for the time. If I'm not mistaken, the switchover—away from using the male pronoun as a gender neutral pronoun—began (very slowly) in the late '70s. I remember reading an article Douglas Hofstadter wrote about how it bothered him once he became aware of the issue, but he'd mostly been oblivious until it was brought to his attention. The article also discussed various solutions to the problem, many of which are now common place (but if I'm not mistaken were fairly novel at the time). I think that article was from '79.
Edit: I was looking for the actual date Hofstadter's article was published, but I'm not sure since all the references I can find to it are from his '85 book Metamagical Themas whose contents was mostly (but not all) re-printing stuff he'd written starting in the late seventies. I noticed (just now) his article was included in a bunch of academic histories of gender in language, so it may be a decent reference point after all. So it looks like the idea to not use the male pronoun this way was pretty novel even in '85, probably.
Not entirely on topic, obviously, but whatever: there's a strange emphasis on the male pronoun in the first paragraph of this, that at first seems like a kind of horrible hiccup from the past, but then, through its repetition, becomes more clearly a sardonic gendering of the programmer-user from above, which is excellent (if true)