The seven programming ur-languages (2021)

I always thought that the "message passing" style of OO (which I always hated as a term, because it implies asynchronicity, but I digress) is firmly something else than the "classes and interfaces" style of OO, and that it's an unfortunate accident of history that we give them the same name.

The comments here are interesting, lots of possibilities for other ur-languages. My suggestion is macro based languages. Macro based programming predates all programming languages other than ASM[1]. The simple macro systems, like early assemblers provided, aren't ur-languages, but once macros can expand other macros and generate definitions of new macros, the macro systems can become general purpose programming systems.

The two earliest macro systems that were clearly designed to be general purpose languages that I know of are Christopher Strachey's GPM[2] and Calvin Mooers TRAC[3] programming language. These languages appeared at roughly the same time, the mid 1960s. I prefer the syntax of TRAC, but otherwise they are almost isomorphic. TRAC was featured in Computer Lib/Dream Machines[4] by Ted Nelson where the author said it was one of the three important languages for programmers to learn. A good introduction to TRAC and it's implementation can be found in Études for Programmers[5].

Other more contemporary examples of macro programming languages are m4, and TeX. LaTeX is programmed in the TeX macro system.

[1] Daniel Weise and Roger Crew, "Programable Syntax Macros", ACM SIGPLAN, 1993, https://dl.acm.org/doi/pdf/10.1145/173262.155105

[2] Christopher Strachey, “A general purpose macrogenerator,” Computer Journal, 8(3), pp. 225-241, 1965

[3] Calvin Mooers, "TRAC, a procedure-describing language for the reactive typewriter", CACM, Vol 9(3), March 1966, pp. 215-219, https://dl.acm.org/doi/10.1145/365230.365270

[4] Ted Nelson, "Computer Lib/Dream Machines", 1974, Self-published. (There is a 2nd edition from Microsoft Press, but I'm only familiar with the 1st edition).

[5] Charles Wetherell, "Études for Programmers", 1978, Prentice Hall. (It's out of print and available from Amazon for $427. I'm going to have to start locking up my old books.)

Oh it’s a ML alright, fits right next to Agda for example.

Not to mention the various graphical programming languages used in industrial control - ladder logic, continuous function chart, and sequential function chart. Ladder in particular is incredibly widespread, as it was a direct descendant of the diagrams used to document and debug relay logic, and was adopted in some of the first PLCs (programmable logic controllers) in the late 60s/early 70s.

Programming PLCs sometimes feels like going to, say, Australia or New Zealand, and being immersed in an environment which went down a different evolutionary tree very on in its development.

Agree on the families, but I would pick a different representative for many of the categories.

Algol -> C. Mostly because you can actually do things with C, and yet it remains a fairly small language that's a relatively pure exemplar of the Algol tradition.

Lisp -> Scheme. Also because it's a tiny language that tries to push the fundamentals of the Lisp family (code-as-data, recursion, functional programming, macros) as far as possible.

ML -> Haskell. ML is eager, Haskell is lazy. If you're going to learn about the ML family, you might as well learn the concept of lazyness, which results in a very different style of programming than FP of the Scheme variety (in the Lisp family).

APL -> J. The usage of special symbols is largely irrelevant to the concepts in APL, and it's a barrier to accessibility. You can learn all the important parts of array-oriented programming with J and use actual words to do it.

Self, Forth, and Prolog I would keep as exemplars of their type. I would also add TCL as another ur-language for string-based scripting languages (with Perl, PHP, and SNOBOL as other representatives of the category).