Lisp: How to write functions

V. How to write functions

The form of the function definition is as follows:

(DEFUN function_name  parameter_list
	function_body )

where:

function_name is an identifier,
parameter_list is a list (possibly empty) of identifiers, and
function_body is an S-expression.

When writing functions, clarity is important, especially with all those parentheses to keep track of. Here are some hints that you may find to be helpful.

When writing a function, begin the first line (containing the name of the function) in column 1. Start all other lines indented by about 10 spaces, so it is easy to scan down the function names.
When writing a conditional, put the word COND on a line all by itself. Put only one clause per line, starting each clause directly under the COND. If you nest a second COND inside the first, indent the nested COND.
Separate the condition and the result of a clause with extra blanks. If a clause takes more than one line, try to break between the condition and the result.
Group closing parentheses according to the lines on which the opening parentheses occurred, with blanks between groups. For example, if the first line of a function has two open parentheses which are not closed on the same line, then the last line should have the two matching close parentheses together, separated from any other parentheses by blanks. If you put COND on a line by itself, then its closing parenthesis should be in a group by itself.