Look 0 of my work involves HTML, well maybe 1-2 percent does; however, about 60% of my work involves regular expressions, grammar, lexical scanning and syntactic parsing, so it still irks me, and will irk me beyond my grave, when people say shit like ‘Don’t parse HTML/Markdown/etc with regex! Use a parser generator!’
So this is stupid, because most people know that HTML and Markdown are not the type of languages that require a push-down parser, or even a simple LL(1) recursive-descent parser! Unless by ‘parser generator’ they mean ‘lexer generator’ or ‘PEG generator’, they are wrong, or at least, partly incorrect.
Like my diabetes, they are not grammatically Type 2 (Chomsky-wise, Context-Free); rather, they are Type 3 (Chomsky-wise, Regular).
It’s preferred if you don’t do a syntax-directed lexical translation of Markdown or HTML, and it’s best if you build a tree. I learned that making Mukette and I am currently using my implementation of ASDL to build a tree. But truth is, unlike Context-Free languages, like any non-markup language, it is ENTIRELY possible to do a syntax-directed translation of HTML and Markdown, using pre-compiled, or runtime-compiled regex.
You will have to introduce states to make it a proper Automata, but even that is not required. I once did a syntax-directed translation of Markdown to HTML in AWK! With just one extra state.
I don’t remember the copypasta that was talk of the town 10 years ago, I was a kid back then (17) and I could not dig it up. But it’s a troll that has stuck with me ever since.
Maybe, just maybe, a PEG paser generator could have been what they meant. But even then, PEG generators generate a recursive-descent parser most of the times.
In fact, I dare you to use Byacc, Btacc, Bison, Racc, PYLR, ANTLR, peg(1), leg(1), PackCC or any of these LALR or LL parser generators to parse a markup language. You’ll have a very bad time, it is not impossible, it’s just an overkill.
TL;DR: Most markup languages, like HTML or Markdown, are best lexed, not parsed! Even if you wish to make a tree out of it. But for syntax-directed translations, REs would do.
Thanks.
PS: If you translate a markup language into a tree, you can translate that tree into other markup languages. That’s what Pandoc does. Pandoc is hands-down the best piece of tool I have laid my hands on.
Not really. You should avoid regexes for almost everything really. They’re too error prone. The only situations where they really shine are where it doesn’t matter too much if they’re wrong. For example interactive editing/filtering/searching. Another place I use them is for triaging error messages.
Using them in a parser for anything more than maybe matching literals in the lexer is insane. (Assuming you care about your code actually working.)