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 wit

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 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.