[Maxatar]

You're going to have a very hard time parsing a language using recursive descent if you don't understand some formal language theory. Recursive descent algorithms have a lot of trouble with left-recursion, and can result in arbitrary backtracking if you're not careful, which can blow up memory and time. To fix left-recursion you need to rewrite your grammar, which means familiarity with formal language theory. To avoid backtracking you typically use an LL(N) or variations thereof, which once again require having a pretty good understanding of formal language theory.

[FeepingCreature]

Nah. Source: have done it without formal language theory. You can do most things by printf debugging and kludging.

(Left-recursion? Use a while loop! Mutable state is a pathway to many abilities functional programmers consider unnatural.)

[PaulHoule]

You can definitely write parsers and lexers knowing just enough to be dangerous.

I remember being in the PHP culture where people wrote regex-based hacks instead of the character-at-a-time or token-at-a-time state machines or state machine + a stack kind of things which would be too slow in a language like that.

The less you know the faster you get in trouble when things get tough.

[Maxatar]

My statement was specific to recursive descent parsing.

[FeepingCreature]

But recursive descent parsing is implemented with functions operating on parser state. The whole point of it is that it's very easy to write a parser because the abstraction exactly matches to function calling in programming languages. So you can do the whole range of pl primitives too.