Tic tac toe/naughts-and-crosses AI in brainfuck
To play, type a number between 1 and 9 to place an X there.
You can find a Live demo here.
I wanted to just release the minimized version and remain mysterious, but it's quite long with a lot of repetition and some people might think that it was transcompiled from something else.
So, here is the original source code with comments that made sense at the time. The choose-a-number script was the first bit I wrote and is in a separate file, included here is the minimized version of it.
Although a perfect AI would have been possible, I deliberately left in a few possible games where the AI can lose. It would be boring otherwise.
One thing I quickly learned while writing this is to use boolean flags as much as possible. Checking if a cell is zero is so much easier than checking if it's exactly one, or two, etc. Another tactic I worked out was to place markers in memory of -1 (or 255). Lots of routines 'get lost' by not leaving the memory pointer in a fixed location, so in order to recover I frequently use things like
+[->+]-
which means, "head right until you reach a cell of value -1". This lets us put reference points in memory that we can always recover to.
This is the interpreter I used for developing this game.