The source for the grammar is the last version of the Algol 60 specification, ISO 1538. A free copy of the spec was hand-translated and then adapted to Antlr4.
Other sources you can find from the Wikipedia page.
The examples included were gathered from various free sources on the Internet.
- https://github.com/erwan-kessler/ALGOL-60/tree/master/examples The samples in this repo are of unknown origin, but they appear valid with only a few simple departures from the Standard in the alphabet (e.g., using backquote and forward quotes instead of upper-left corner and upper-right corner characters). The grammar is tuned to these examples.
- https://github.com/hxw/Elliott-803/tree/main/Algol60-Samples The samples in this repo came some old tapes the author squirreled away, for an Elliott-803. The Algol 60 compiler and examples departs from the standard in various ways: use of single quote instead of semi-colon. The samples are not used here.
- https://github.com/JvanKatwijk/algol-60-compiler The samples in this Algol-60 compiler source, written by Jan van Katwijk, are described in the User Manual. It is a derivative of the ”Modified Report on the algorithmic language ALGOL 60” (downloadable from here). Some of the samples are included in the tests here, but others are not because they deviate from the spec, e.g., a semi-colon after an "end".