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(emacs-lisp-intro.info)append-to-buffer body

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The Body of `append-to-buffer'
------------------------------

   The body of the `append-to-buffer' function begins with `let'.

   As we have seen before (Note: `let'.), the purpose of a `let'
expression is to create and give initial values to one or more
variables that will only be used within the body of the `let'.  This
means that such a variable will not be confused with any variable of
the same name outside the `let' expression.

   We can see how the `let' expression fits into the function as a
whole by showing a template for `append-to-buffer' with the `let'
expression in outline:

     (defun append-to-buffer (buffer start end)
       "DOCUMENTATION..."
       (interactive "BAppend to buffer: \nr")
       (let ((VARIABLE VALUE))
             BODY...)

   The `let' expression has three elements:

  1. The symbol `let';

  2. A varlist containing, in this case, a single two-element list,
     `(VARIABLE VALUE)';

  3. The body of the `let' expression.

   In the `append-to-buffer' function, the varlist looks like this:

     (oldbuf (current-buffer))

In this part of the `let' expression, the one variable, `oldbuf', is
bound to the value returned by the `(current-buffer)' expression.  The
variable, `oldbuf', is used to keep track of the buffer in which you
are working and from which you will copy.

   The element or elements of a varlist are surrounded by a set of
parentheses so the Lisp interpreter can distinguish the varlist from
the body of the `let'.  As a consequence, the two-element list within
the varlist is surrounded by a circumscribing set of parentheses.  The
line looks like this:

     (let ((oldbuf (current-buffer)))
       ... )

The two parentheses before `oldbuf' might surprise you if you did not
realize that the first parenthesis before `oldbuf' marks the boundary
of the varlist and the second parenthesis marks the beginning of the
two-element list, `(oldbuf (current-buffer))'.