Nicholas Carlini wrote a 2-ply minimax chess engine with 84,688 regular expressions. It's not a massive mangled choose-your-own adventure through common openings made of if conditions: it follows the rules of chess and plays straightforward material-grabbing moves.
So how are we going to get regular expressions to play chess? Well, by making a regular expression computer, of course! More specifically, we're going to design a Branch-Free, Conditional-Execution, Single-Instruction Multiple-Data instruction set. And then make a sequence of regular expressions that interpret these instructions. (Kind of like a GPU instruction set. And a bit of ARM. But a lot slower.) And then from there we can program our new computer to play chess. So let's get started.
(Some people may say I have an unhealthy obsession with building weird computers, c.f. my game of life computer or my printf computer. Those people are wrong, and just have an unhealthy obsession with the banal and ordinary.)
Looking at the regexes is agony. Some brains are just much larger than mine and Carlini's is one of them.
I guess I'll just say that I think more people should do entirely pointless things like this. It's a lot of fun, no one cares how long it takes you to finish, no one cares if it works or not, and incidentally, it teaches you more than you wanted to know about dozens of areas of computer science outside your field.
Previously:
• How to play chess like an asshole
• Making a Warhammer 40,000 chess set and board
• I love watching this chess player crush obnoxious dudes
• Chess pieces made from nuts and bolts
