That's not true, though. When running in the REPL (the most common way to interface with Lisp) the compile time and runtime Lisps are the same. For example, h

That's not true, though. When running in the REPL (the most common way to interface with Lisp) the compile time and runtime Lisps are the same. For example, here's a copy/paste from a REPL session that defines a macro that defines a function. The macro (at "compile time") prints information about the function (just its argument count) to stdout before using defun (itself a macro) to actually define the function. Next I call the new function and print out a disassembly, just to show the function is in fact compiled "CL-USER> " is the prompt in the REPL I use: CL-USER> (defmacro my-defun (name arguments &body body) (format t "Defining ~a, taking ~a arguments~%" name (length arguments)) `(defun ,name ,arguments ,@body)) MY-DEFUN CL-USER> (my-defun omg-2 (value) (* value value)) Defining OMG-2, taking 1 arguments OMG-2 CL-USER> (omg-2 34) 1156 CL-USER> (disassemble #'omg-2) ; disassembly for OMG-2 ; Size: 33 bytes. Origin: #x52ED2714 ; OMG-2 ; 14: 498B5D10 MOV RBX, [R13+16] ; thread.binding-stack-pointer ; 18: 48895DF8 MOV [RBP-8], RBX ; 1C: 488BD6 MOV RDX, RSI ; 1F: 488BFE MOV RDI, RSI ; 22: FF1425C0001052 CALL QWORD PTR [#x521000C0] ; GENERIC-* ; 29: 488B75F0 MOV RSI, [RBP-16] ; 2D: 488BE5 MOV RSP, RBP ; 30: F8 CLC ; 31: 5D POP RBP ; 32: C3 RET ; 33: CC10 INT3 16 ; Invalid argument count trap NIL CL-USER> It is also possible to compile a Lisp program to an executable (or byte code or whatever) and run it, and not use the dynamic aspect of it.