14.4 Count Several defuns Within a File

A file such as simple.el may have a hundred or more function definitions within it. Our long term goal is to collect statistics on many files, but as a first step, our immediate goal is to collect statistics on one file.

The information will be a series of numbers, each number being the length of a function definition. We can store the numbers in a list.

We know that we will want to incorporate the information regarding one file with information about many other files; this means that the function for counting definition lengths within one file need only return the list of lengths. It need not and should not display any messages.

The word count commands contain one expression to jump point forward word by word and another expression to count the jumps. The function to return the lengths of definitions can be designed to work the same way, with one expression to jump point forward definition by definition and another expression to construct the lengths’ list.

This statement of the problem makes it elementary to write the function definition. Clearly, we will start the count at the beginning of the file, so the first command will be (goto-char (point-min)). Next, we start the while loop; and the true-or-false test of the loop can be a regular expression search for the next function definition—so long as the search succeeds, point is moved forward and then the body of the loop is evaluated. The body needs an expression that constructs the lengths’ list. cons, the list construction command, can be used to create the list. That is almost all there is to it.

Here is what this fragment of code looks like:

(goto-char (point-min))
(while (re-search-forward "^(defun" nil t)
  (setq lengths-list
        (cons (count-words-in-defun) lengths-list)))

What we have left out is the mechanism for finding the file that contains the function definitions.

In previous examples, we either used this, the Info file, or we switched back and forth to some other buffer, such as the *scratch* buffer.

Finding a file is a new process that we have not yet discussed.