defun is a macro in the Lisp family of programming languages that defines a function
Subroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
In computer programming, a global variable is a variable that is accessible in every scope . Interaction mechanisms with global variables are called global environment mechanisms...
that uses the form:
(defun (...)
functionbody)
Defining the function addnumbers that adds two numbers:
;; Define a function that adds two numbers together:
(defun addnumbers (number1 number2)
(+ number1 number2))
(addnumbers 5 4)
9
defining function square that squares a number:
;; Define a function that squares a number:
(defun square (x)
(* x x))
and defining a function that returns the factorial
Factorial
In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n...
of a number:
(defun factorial (number)
(if (= number 1)
1
(* number (factorial (- number 1)))))
(factorial 6)
720
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
Emacs Lisp is a dialect of the Lisp programming language used by the GNU Emacs and XEmacs text editors . It is used for implementing most of the editing functionality built into Emacs, the remainder being written in C...
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