Question about lambda

[August]

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.

[ramarren]

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 ...)).

[August]

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?

[ramarren]

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.

[August]

OK, thanks much for the help!

[findinglisp]

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 ...).