jemarch

The core Algol 68 language is indeed set in stone.

But we are carefully adding many GNU extensions to the language, as was explicitly allowed by the Revised Report:

  [RR page 52]
  "[...] a superlanguage of ALGOL 68 might be defined by additions to
   the syntax, semantics or standard-prelude, so as to improve
   efficiency or to permit the solution of problems not readily
   amenable to ALGOL 68."

The resulting language, which we call GNU Algol 68, is a strict super-language of Algol 68.

You can find the extensions currently implemented by GCC listed at https://algol68-lang.org/

I would recommend the Informal Introduction to Algol 68, available in PDF at https://algol68-lang.org/resources

You can find some modern Algol 68 code, using the modern stropping which is the default in GCC, at https://git.sr.ht/~jemarch/godcc

Godcc is a command-line interface for Compiler Explorer written in Algol 68.