= LightningBF It's an implementation of the language whose name is not to be mentioned in polite company. You know the one. There's a nice article about it here: http://esoteric.voxelperfect.net/wiki/BF , which provides a few trivial sample snippets, and links to more code, including decidedly non-trivial programs. A few small examples that were used to test the implementation are in the bf/ subdirectory. = For the already-initiated If you already know all you need to know about that language, then the summary on the open-to-interpretation parts are as follows: * The pointer doesn't wrap, so you can segfault if you aren't careful. * You get 640 * 2^10 cells. 640k ought to be enough for anybody. * EOF on read() is a zero byte. * Characters that are not one of the 8 BF commands are ignored. And then you can skip the rest, unless you're one of the uninitiated. = A simple description of the language You get an array of cells, all one byte in size, and all initialized to zero. You also get a pointer, and it starts at the first cell. It has 8 commands, and that's all it does: + Increments the current cell by 1. - Decrements the current cell by 1. > Move the pointer to the next cell. < Move the pointer to the previous cell. [ If the current cell is 0, skip to the matching ]. ] If the current cell is non-zero, jump to the matching [. , Read a byte from stdin into the current cell. . Print the byte in the current cell to stdout. The 8 commands are roughly equivalent to the following C code: + *ptr++; - *ptr--; > ptr++; < ptr--; [ while(*ptr) { ] } , *ptr = 0; read(0, ptr, 1); . write(1, ptr, 1); In fact, that's (roughly) how they're implemented. And after all of that, you have a fun, esoteric (but Turing-complete) language. = Implementation The basic process the compiler goes through is to read the input file, one byte at a time, generate one batch of machine-language instructions for each valid input character, and when it's done, execute the generated machine code. The reason LightningBF was implemented to begin with was so that I could play around a little more with GNU Lightning. The name isn't meant to imply that the compiler is fast or generates fast code; it just uses Lightning. It's not very well documented, but should serve as a fairly simple introduction to Lightning if you have a reference ready. (Also, I found the current version of lightning to be a little hard to locate, and 1.2 is a fairly old release (no x86-64!), so you may find this link helpful: http://savannah.gnu.org/git/?group=lightning .) In fact, the compiler is fairly trivial. It's a fairly straightforward, easy to read implementation of a JIT-compiler for the language, and absolutely zero optimization is performed. (Some low-hanging optimization fruit: strings of +s or -s could, instead of load/inc-or-dec-by-1/store, be done with only one load, an increment or a decrement by the number of +s or -s, and one store.) = License Public domain. It's trivial code. I wrote it to get a little more familiar with Lightning. A copy of Lightning is distributed along with this code. Its license is the LGPL, and a copy of the LGPL and the GPL is in the lightning directory.