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(emacs-lisp-intro.info)Several files recursively

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Recursively Count Words in Different Files
==========================================

   Besides a `while' loop, you can work on each of a list of files with
recursion.  A recursive version of `lengths-list-many-files' is short
and simple.

   The recursive function has the usual parts: the `do-again-test', the
`next-step-expression', and the recursive call.  The `do-again-test'
determines whether the function should call itself again, which it will
do if the `list-of-files' contains any remaining elements; the
`next-step-expression' resets the `list-of-files' to the CDR of itself,
so eventually the list will be empty; and the recursive call calls
itself on the shorter list.  The complete function is shorter than this
description!

     (defun recursive-lengths-list-many-files (list-of-files)
       "Return list of lengths of each defun in LIST-OF-FILES."
       (if list-of-files                     ; do-again-test
           (append
            (lengths-list-file
             (expand-file-name (car list-of-files)))
            (recursive-lengths-list-many-files
             (cdr list-of-files)))))

In a sentence, the function returns the lengths' list for the first of
the `list-of-files' appended to the result of calling itself on the
rest of the `list-of-files'.

   Here is a test of `recursive-lengths-list-many-files', along with
the results of running `lengths-list-file' on each of the files
individually.

   Install `recursive-lengths-list-many-files' and `lengths-list-file',
if necessary, and then evaluate the following expressions.  You may
need to change the files' pathnames; those here work when this Info
file and the Emacs sources are located in their customary places.  To
change the expressions, copy them to the `*scratch*' buffer, edit them,
and then evaluate them.

   The results are shown after the `=>'.  (These results are for files
from Emacs Version 21.0.100; files from other versions of Emacs may
produce different results.)

     (cd "/usr/local/share/emacs/21.0.100/")
     
     (lengths-list-file "./lisp/macros.el")
          => (273 263 456 90)
     
     (lengths-list-file "./lisp/mail/mailalias.el")
          => (38 32 26 77 174 180 321 198 324)
     
     (lengths-list-file "./lisp/makesum.el")
          => (85 181)
     
     (recursive-lengths-list-many-files
      '("./lisp/macros.el"
        "./lisp/mail/mailalias.el"
        "./lisp/makesum.el"))
            => (273 263 456 90 38 32 26 77 174 180 321 198 324 85 181)

   The `recursive-lengths-list-many-files' function produces the output
we want.

   The next step is to prepare the data in the list for display in a
graph.