[rsc]

Perhaps this comment was meant as a joke, but this is exactly what lex does for regexps and yacc does for LALR(1) grammars. For the right job, they are both great.

I watched Ken Thompson write a Paxos implementation in yacc once.

[rhelz]

> Perhaps this comment was meant as a joke

Nope, not a joke. As you say, this is just the application of parsing technology to a tokenized stream of input events.

its super-useful in creating state machines to do parsing---and it can be super-useful to create state machines for other things as well.

> I watched Ken Thompson write a Paxos implementation in yacc once.

In real time? dude, you gotta post video to youtube or post a "Tell HN" story about it.

[rsc]

It's not as exciting as it sounds. He wanted to play around with learning Paxos, which is a big state machine, and he used yacc to do it. I shared an office with him for a couple years in the early days of Go, and he was working on it while I was working on other things. I helped him track down at least one bug in the Go port of yacc that way. I think the grammar he was writing was completely regular, but yacc is nicer to use than lex.

Ken discussed yacc briefly in Coders at Work, which I quoted at https://research.swtch.com/yyerror:

Seibel: And are there development tools that just make you happy to program?

Thompson: I love yacc. I just love yacc. It just does exactly what you want done. Its complement, lex, is horrible. It does nothing you want done.

Seibel: Do you use it anyway or do you write your lexers by hand?

Thompson: I write my lexers by hand. Much easier.

[rhelz]

> It's not as exciting as it sounds.

De Gustibus. Some of us are into that sort of thing. Thanks for the link.

> Thompson: I write my lexers by hand. Much easier.

LMAO. If you've been doing it since the 60's, I suppose you get the hang of it:

Ken Thompson, “Regular expression search algorithm,” Communications of the ACM 11(6) (June 1968), pp. 419–422