You might have seen Minecraft used to teach programming or mods that allow some in-game programming, but writing BASIC code inside Minecraft? That's virtually unheard of... until now. SethBling has created a BASIC interpreter that allows you to compile and run simple programs and scripts within Mojang's world-building game. It's easy to use many blocks of commands however, it's effective. Minecraft Servers You can print text, and include in-game robots ("turtles") complete tasks. Do you require digging a long tunnel to complete your project? Start an excavation script and let the bot do all the work.
It's not possible to write complex software in a world that wasn't intended for it. The game's operating speed of 20Hz renders code slow. It can only execute 20 commands per second and it becomes slower the more you use it. However, you don't need to create a whole week of the interpreter yourself -- SethBling has published the necessary material, so it's just to install the add-on, and then brushing up on your IF/THEN expressions.