On lambda function

Here's a function that takes a number N, and returns a function that adds N to its argument (taken from Practical Common Lisp):

(defun add-n (n)
	#'(lambda (x)
		(+ x n)))

My guess was something like this should work:

((add-n 1) 2)

Unfortunately, it doesn't work. Further investigation:

? (functionp 'add-n)
NIL

Now I'm confused. How can I use this add-n properly?

anta40 wrote:Here's a function that takes a number N, and returns a function that adds N to its argument (taken from Practical Common Lisp):

(defun add-n (n)
	#'(lambda (x)
		(+ x n)))

My guess was something like this should work:

((add-n 1) 2)

Unfortunately, it doesn't work. Further investigation:

? (functionp 'add-n)
NIL

Now I'm confused. How can I use this add-n properly?

(first, it's not a lambda function. It is either anonymous function or a lambda expression)

'add-n is a symbol. But #'add-n is a function. (add-n 10) is also a function.
The expression ((add-n 1) 2) works in scheme, in common lisp you should use funcall:

(funcall (add-n 1) 2)

(For details, see information about Lisp-1 vs Lisp-2)

Yeah that works. Thanks for you explanation.

BTW, I did tried this, and also failed:

(funcall #'+(add-n 1) 2)

Probably because add-n is just an anonymous function?

anta40 wrote:Yeah that works. Thanks for you explanation.

BTW, I did tried this, and also failed:

(funcall #'+(add-n 1) 2)

Probably because add-n is just an anonymous function?

Add-n is a function. (add-n 1) is an expression that when evaluated returns the anonymous function.
#' is a "function designator". You should use it only in two cases: #'x where x is a symbol or #'(lambda (args) body).

Ah OK. I think I understand it.

You won't fully understand until you read the following snippet of the spec.
http://www.lispworks.com/documentation/ ... 02_dhb.htm