Recursive language

Have you ever heard the story of the Russian dolls? You know, the dolls where one fits inside the other, and so on? Recursion is sort of like that. A recursive language is a language that can talk about itself, sort of like a doll talking about another doll that's inside of it.

Let's say you have a rule in your language that says "if you see the word 'cat', replace it with 'dog'". That's a simple rule, right? But what if your language also has a rule that says "if you see the word 'dog', replace it with 'cat'"? That's recursion!

When you use the second rule, it will find the word 'dog' and replace it with 'cat'. But then the first rule will kick in and replace that new 'cat' with 'dog' again! This can go on and on forever!

So that's what recursion is. It's when something refers to itself, and can keep doing that over and over again. It's like a never-ending game of "telephone". With recursion, sometimes you can get stuck in an infinite loop, where the rule just keeps repeating and repeating without ever stopping. But when done correctly, it can be a very useful tool for creating complex languages and systems.