If you look at code with really low-level operators like CAR, CDR, CONS, ATOM, NULL, etc then this is the assembly level of Lisp. If you look at some Lisp Machi

If you look at code with really low-level operators like CAR, CDR, CONS, ATOM, NULL, etc then this is the assembly level of Lisp. If you look at some Lisp Machines, which had a processor with a for Lisp optimized instruction set, many of those mapped relatively direct to corresponding machine instructions - using a mostly stack machine. The CLISP implementation of Common Lisp has a virtual machine implementation. Let's take some simple demonstration code: [1]> (defun foo (a) (car (cdr (if (null a) '(1 2) (cons 3 a))))) FOO Now we compile it for the CLISP virtual machine: [2]> (compile 'foo) FOO ; NIL ; NIL If we look at the disassembled virtual machine code, you'll see that the machine code has actually similar primitives for its stack machine: [3]> (disassemble 'foo) Disassembly of function FOO (CONST 0) = (1 2) (CONST 1) = 3 1 required argument 0 optional arguments No rest parameter No keyword parameters 11 byte-code instructions: 0 (LOAD&JMPIFNOT 1 L10) 3 (CONST&PUSH 1) ; 3 4 (LOAD 2) 5 (CONS) 6 L6 6 (CDR) 7 (CAR) 8 (SKIP&RET 2) 10 L10 10 (CONST 0) ; (1 2) 11 (JMP L6) NIL Unrelated to that there is also the idea to program assembler code embedded in Lisp - this is often called LAP code (Lisp Assembler Program). Several implementations are using this.