> (car (lambda (a b) (+ a b))) An interpreted function in a Common Lisp cannot literally just be a lambda expression list, because that would not satisfy the t

> (car (lambda (a b) (+ a b))) An interpreted function in a Common Lisp cannot literally just be a lambda expression list, because that would not satisfy the type system. It has to be of type function and a function is not a subtype of list. What happens is that there is some container object which says "I'm an (interpreted) function", which has slots that hold the raw source code. It might not be a lambda form; for instance, the original lambda might be destructured into parameters and body that are separately held. There is some API by which the interpreter gets to those pieces and then it's just recursing over the nested lists. > Another good test is to construct a function at runtime and try to call it. Common Lisp doesn't provide a standard API for constructing an interpreted function (or even make provisions for the existence of such a thing). Lisps that have interpreted functions may expose a way for application code to construct them without having to eval a lambda expression. It's just a matter of constructing that aforementioned container object and stuffing it with the code piece or pieces. If that is possible then that object is something you can call. When you call that function, eval ends up used anyway.