DEFUN defines a function with name
You can define a named function using the DEFUN form:
(defun sum (x y)
(+ x y))
The defun form has the following arguments:
- The name of the function: sum
- A list of argument names: x y
- The body of the function: (+ x y)
DEFUN returns the name of the defined function, so we have a sum as function.
Now we are going to review the lambda.
LAMBDA defines anonymous functions
Lisp lets you create an unnamed, or anonymous, function using the LAMBDA form:
(lambda (x y)
(+ x y))
The lambda form has the following arguments:
- A list of the arguments names: x y
- The body of the lambda: (+ x y)
I ask me, how can I call or use the lambda?, well I could do this:
((lambda (x y)
(+ x y)) 1 2)
or
(funcall (lambda (x y)
(+ x y)) 1 2)
Other examples:
I have a list like this (1 2 3 4 5), so I want to add 1 all of them, then the result will be (2 3 4 5 6)
How can I do that?
We are going to use mapcar with a lambda:
(mapcar (lambda (x) (+ x 1)) '(1 2 3 4 5))
Now I have a list like this: ((9 2 7 5) (7 2 0 9) (10 1 0 21 15 )), so I want to sort the list like this ((2 5 7 9) (0 2 7 9) (0 1 10 15 21))
(mapcar (lambda (x) (sort x #'< )) '((9 2 7 5) (7 2 0 9) (10 1 0 21 15 )))
