I'm not sure what exactly you're referring to, but one avenue to implement AI is genetic programming, where programs are manipulated to reach a goal.

Lisp languages are great for these manipulations, since the AST being manipulated is the same data structure (a list) as everything else. In other words, genetic programming can lean into Lisp's "code is data" paradigm.

As others mentioned, today everything is based on neural networks, so people aren't learning these other techniques.