Question about lambda

On my Lisp journey, there is something about lambda that has been bugging me.

;; This works, as expected.
((lambda (n) (* n n)) 3)

;; This doesn't work, as expected;
(#'(lambda (n) (* n n)) 3)

;; This works, as expected.
(mapcar #'(lambda (n) (* n n)) '(1 2 3))

;; Why does this work also?
(mapcar (lambda (n) (* n n)) '(1 2 3))

I didn't expect this last case to work, assuming that you need to get the function value of the lambda to pass it as an argument.

In operator position (as considered by the evaluator) LAMBDA is not treated specially, as it is when it is in a form in function name position (as in the first and third of your examples), but rather as a perfectly standard macro which expands to (function (lambda ...)).

Thanks Ramarren. I guess I need to read through the hyperspec more thoroughly

Style-wise, do people generally use the #' when using lambda as a function argument and when returning a lambda from a function?

I do not believe there is consensus on this. I personally like to use #' to additionally indicate that an anonymous function is returned. Since the LAMBDA macro was added relatively late in the standardisation process this can be considered "old-style", but Practical Common Lisp uses it as well.

OK, thanks much for the help!

August wrote:Style-wise, do people generally use the #' when using lambda as a function argument and when returning a lambda from a function?

Generally, yes, people use #'(LAMBDA ...).