[farva]

There's been a lot of discussion about the minimal set of primitives to build an interpreter in the Forth community (for instance https://groups.google.com/d/msg/comp.lang.forth/KHw28PKZXUk/.... ) Particularly interesting is eForth, a Forth made to be easily ported while still having acceptable performance, and Minimal ANS Forth, a heavily-commented ANS compliant Forth written in Forth (both of these use significantly more than the minimum for practical reasons.) The answer, for both Lisp and Forth, is somewhere between 8 and 11. In "real world" usage, the set of primitives largely depends on the hardware you're targeting and how well you need it to perform.

[upofadown]

The Forth exercise is interesting because you end up with a super simple instruction set. If someone ever invents a machine that can do operations really fast, but where implementing complex operations is prohibitive, such exercises could have practical value.