It was thus said that the Great Shawn T. Rutledge once stated: Sure, I'll bite (Hmmmmm, yummmmmm but what's this sharp pointy thing? 8-) Instructions to help with pointer manipulations. Also a typed architecture would help as well. There isn't much in a LISP interpreter and a fairly minimalistic one can be written in a few hundred lines of code (although it'll probably be slow). The stack is implicit---you don't really use one explicitely (much like you don't really notice the stack when you make subroutine calls but it's used implicitely to keep track of return addresses). The basic storage unit (a cons cell is the traditional name) might look something like: typedef struct conscell { int type; union alltypes data; struct conscell *next; } conscell_t; A Lisp list is basically, a linked list of conscells with type information. If you can keep all this in a single word of memory that helps with memory consumption, and possibly specialized instructions to extract the fields out to help with speed, and possibly instructions to insert, delete and walk linked lists. I know the VAX had linked-list instructions. -spc (Have compiler, will code)