Guy Steele on designing a programming language for library building (OOPSLA ’98 keynote)

Classic, and timeless. (HT: Tony Van Eerd and Peter Sommerlad)

Note that when he says “growing a language” he doesn’t mean literally the language itself — it’s not a talk about language evolution. Rather, he’s talking about enabling users to write rich and powerful abstractions in that language without having to go beg their language designer and compiler vendor to build them into the compiler every time.

Steele’s argument in the back half of the talk is on point, on the importance of imbuing a programming language with a few well-chosen “patterns” that allow, and guide, specific kinds of extensibility. His argument is a great description of why I’m pursuing metaclasses for C++, because we should have a convenient way for programmers to write their own Words of Power like “value_type” or “interface” as libraries instead of forcing them to go bother their local compiler writer (or local standards committee) for a language extension each time for that sort of thing. And his “as a pattern” description is a great summary of why I’m proposing them as “just” a sugar to apply a compile-time function in a very specific place and in a very constrained way, and not going anywhere near making a mutable language which would be crazy not worth pursuing.