Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes: They can and they don't. Accessors like `person-name' normally check their arguments (effectively using `person-p') and signal an error if the argument is the wrong type. This check is affected by `(optimize (safety ...))' declarations. Safety level 1, the default, uses a somewhat optimized check that will detect all incorrect arguments, but may use an uninformative error message (e.g., "expected a vector" instead of "expected a `person'"). Safety level 0 omits all checks except as provided by the underlying `aref' call; safety levels 2 and 3 do rigorous checking that will always print a descriptive error message for incorrect inputs. Test it like this. Create a file, say x.el, with the following contents: (proclaim '(optimize (speed 3) (safety 0))) (defstruct (foo) (bar nil) (count 0)) (defun test (x) (foo-count x)) Byte-compile it and load-file x.elc. Then try: (disassemble 'test) byte code for test: args: (x) 0 varref x 1 constant 2 2 aref 3 return So foo-count is inlined and there are no safety checks. Note that #'foo-count is still a regular function, not a macro, meaning you can feed it to #'mapcar etc. But when you *compile* the stuff, the CL additions to the compiler do the right thing. cl.el is smarter than you think. Good enough? :-)