I have a cherished (really) old piece of code, the APL\11 interpreter, originally written by Ken Thompson. It has gone through several incarnations. My version is at [email protected]:gregfjohnson/aplette. I did a rewrite to make it work with 64-bit CPU's and compilers. It leaks memory like a sieve. There was some logic for memory management and garbage collection in the original code, but that has ended up broken over the course of multiple rewrites by multiple people. I'm thinking of integrating Boehm-Demers-Weiser to deal with the memory leak issues. Coincidentally, I had the honor of being acquainted with two of the three authors, Alan Demers and Mark Weiser.