A while ago, I found a website with a simple but devilishly difficult puzzle: given a minimal "programming" language, write a quine. Unfortunately I've since forgotten where to find the puzzle, so I rewrote it myself.
The language mentioned above is composed of two primitives:
print M: print the followingMlines of input verbatim (and don't interpret them)repeat M N: print the lastMlines of output verbatim, startingNlines before the end of output.
As it turns out, these two primitives make up the LZ77 decompression algorithm used to unpack ZIP files, and so if you can make a quine out of these, you can theoretically write a ZIP file that unzips to itself. Cool beans!
Further reading (spoiler alert for those attempting the quine puzzle):
