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Source code for my entry in the 2012 ICFP Programming Competition
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Celestial Dire Badger is: Jed Davis <firstname.lastname@example.org> The strategy here is essentially a glorified random walk. The world step function is applicative, by way of the RCS-like difference list graph structure in mine.rs (which was a learning experience in Rust to get past the language statics); taking advantage of this, the program maintains a collection of world states and repeats randomly picking one, extending it, and replacing a random member of the collection with it. Elaborations on this strategy perform surprisingly well for something so aggressively unenlightened. More specifically: randbot is an unenlightened implementation of this, although it does have some tweaks to favor moving in the same direction and disfavor reversing, relative to the previous move. It does surprisingly well despite that. The more advanced version, and the current submission, is evobot, which attempts to take a more evolutionary approach by granting extra replications to states which have found lambdas. (Various other incentives -- moving rocks directly or indirectly, and exploring parts of the map not recently touched, have been tried and found to be counterproductive. It is difficult to describe the feeling of watching the 'R' knock the falling rock out of the way in midair on contest5.map, and then proceed to go and push the other rock onto the lift it just saved.) (But, after the last parenthetical was written, a number of adjustments for the extension features were added, and seem to be pulling something not entirely unlike their weight.) It also has a few adjustments in terms of not replicating every turn and not switching to another state every replication, which were a modest improvement. (And ignore weightbot; it was an abortive experiment with a fancier "natural selection" approach, which wasn't going to work without a bunch of complicatedness I didn't want to to try to write.) The code in botshell.rs handles the interface with the world: collecting states and retaining the highest-scoring one encountered (and a trace of how to get there), checking for signals (via a C shim, because Rust doesn't seem to have an interface and I can't blame the people working on it for not wanting to touch that without some serious thought), and arranging to respond to the out-of-time signal by writing the best trace and exiting cleanly. There are also two simulator frontends. The simpler is maprun, which takes a route on standard input and a map file on the command line, and prints out each state (currently missing some of the metadata) and the end result. It can be used interactively by putting the terminal into non-canonical non-echoing mode (e.g. `stty cbreak -echo`, but be careful with this if your shell doesn't reset the terminal flags before prompting for input the way zsh does), or if piped into a pager in a terminal of the correct height used as a sort of rudimentary flipbook for perusing a generated route. The fancy way to interact with the game is rlrun, a roguelike-like interface which emits VT/ANSI-style terminal escapes (xterm works). It accepts the vi keys for motion, '-' for undo, and vi-style 'm' and "'" to set and jump to marks -- which in this case are not cursor positions but world states. When quitting, it shows the best state reached and prints the route to it. It's sort of like being a time-travelling robot in a complicated alternate universe plot. A final word on the world simulation, in case it breaks when I least expect it: the map update is limited to what is hopefully a conservative approximation of the area that could be affected by robot movement or by rocks in motion during the last timestep.