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(emacs-lisp-intro.info)Switching Buffers


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Switching Buffers
=================

   The `other-buffer' function actually provides a buffer when it is
used as an argument to a function that requires one.  We can see this
by using `other-buffer' and `switch-to-buffer' to switch to a different
buffer.

   But first, a brief introduction to the `switch-to-buffer' function.
When you switched back and forth from Info to the `*scratch*' buffer to
evaluate `(buffer-name)', you most likely typed `C-x b' and then typed
`*scratch*'(1) when prompted in the minibuffer for the name of the
buffer to which you wanted to switch.  The keystrokes, `C-x b', cause
the Lisp interpreter to evaluate the interactive function
`switch-to-buffer'.  As we said before, this is how Emacs works:
different keystrokes call or run different functions.  For example,
`C-f' calls `forward-char', `M-e' calls `forward-sentence', and so on.

   By writing `switch-to-buffer' in an expression, and giving it a
buffer to switch to, we can switch buffers just the way `C-x b' does.

   Here is the Lisp expression:

     (switch-to-buffer (other-buffer))

The symbol `switch-to-buffer' is the first element of the list, so the
Lisp interpreter will treat it as a function and carry out the
instructions that are attached to it.  But before doing that, the
interpreter will note that `other-buffer' is inside parentheses and
work on that symbol first.  `other-buffer' is the first (and in this
case, the only) element of this list, so the Lisp interpreter calls or
runs the function.  It returns another buffer.  Next, the interpreter
runs `switch-to-buffer', passing to it, as an argument, the other
buffer, which is what Emacs will switch to.  If you are reading this in
Info, try this now.  Evaluate the expression.  (To get back, type `C-x
b <RET>'.)(2)

   In the programming examples in later sections of this document, you
will see the function `set-buffer' more often than `switch-to-buffer'.
This is because of a difference between computer programs and humans:
humans have eyes and expect to see the buffer on which they are working
on their computer terminals.  This is so obvious, it almost goes
without saying.  However, programs do not have eyes.  When a computer
program works on a buffer, that buffer does not need to be visible on
the screen.

   `switch-to-buffer' is designed for humans and does two different
things: it switches the buffer to which Emacs' attention is directed;
and it switches the buffer displayed in the window to the new buffer.
`set-buffer', on the other hand, does only one thing: it switches the
attention of the computer program to a different buffer.  The buffer on
the screen remains unchanged (of course, normally nothing happens there
until the command finishes running).

   Also, we have just introduced another jargon term, the word "call".
When you evaluate a list in which the first symbol is a function, you
are calling that function.  The use of the term comes from the notion of
the function as an entity that can do something for you if you `call'
it--just as a plumber is an entity who can fix a leak if you call him
or her.

   ---------- Footnotes ----------

   (1) Or rather, to save typing, you probably typed just part of the
name, such as `*sc', and then pressed your `TAB' key to cause it to
expand to the full name; and then typed your `RET' key.

   (2) Remember, this expression will move you to your most recent
other buffer that you cannot see.  If you really want to go to your
most recently selected buffer, even if you can still see it, you need
to evaluate the following more complex expression:

     (switch-to-buffer (other-buffer (current-buffer) t))

In this case, the first argument to `other-buffer' tells it which
buffer to skip--the current one--and the second argument tells
`other-buffer' it is OK to switch to a visible buffer.  In regular use,
`switch-to-buffer' takes you to an invisible window since you would
most likely use `C-x o' (`other-window') to go to another visible
buffer.


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