eintr: append-to-buffer body
4.4.2 The Body of ‘append-to-buffer’
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The body of the ‘append-to-buffer’ function begins with ‘let’.
As we have seen before (
‘let’ 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 ...)
(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))’.
Info Catalog
eintr: append interactive
eintr: append-to-buffer
eintr: append save-excursion