Right, CFGs are insufficient for most languages, and yacc is also insufficient for most languages. Yacc is simultaneously less powerful and more powerful than

Right, CFGs are insufficient for most languages, and yacc is also insufficient for most languages. Yacc is simultaneously less powerful and more powerful than CFGs. Less powerful because it uses the LALR(1) subset of CFGs, and more powerful because you can embed arbitrary code with semantic actions. I think the OP is looking for something more like this. This paper is from the same author as Nix, so he has some credibility. But I think this paper is not well written, and I'm not sure about the underlying ideas either. (The output of these pure declarative parsers is more complicated to consume as far as I remember.) Still, the paper does shows how much more there is to consider than "BNF". Thinking "BNF" will solve the problem is a naive view of languages, and as you point out, is very similar to the problem with not understanding what languages "regexes" can express. http://eelcovisser.org/post/135/pure-and-declarative-syntax-definition%3A-paradise-lost-and-regained http://eelcovisser.org/post/135/pure-and-declarative-syntax-... Mainstream parser generators pose restrictions on syntax definitions that follow from their implementation algorithm. They hamper evolution, maintainability, and compositionality of syntax definitions.