Lisp is far from any lambda calculus, even the untyped one. Lambda calculi don't have variadic functions, or any means to inspect their own syntax. Lambda abstraction is called abstraction for a reason - you can't inspect the expression inside. Lisp is really its very own kind of thing, which can be both very interesting (if you care about extensibility) and very irritating (if you care about abstraction). Racket, a dialect of Scheme, is the only serious attempt so far at providing an extensible language that protects user-defined abstractions.