(xemacs.info)Lisp Interaction

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22.6 Lisp Interaction Buffers
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The buffer `*scratch*', which is selected when Emacs starts up, is
provided for evaluating Lisp expressions interactively inside Emacs.
Both the expressions you evaluate and their output goes in the buffer.

   The `*scratch*' buffer's major mode is Lisp Interaction mode, which
is the same as Emacs-Lisp mode except for one command, <LFD>.  In
Emacs-Lisp mode, <LFD> is an indentation command.  In Lisp Interaction
mode, <LFD> is bound to `eval-print-last-sexp'.  This function reads
the Lisp expression before point, evaluates it, and inserts the value
in printed representation before point.

   The way to use the `*scratch*' buffer is to insert Lisp expressions
at the end, ending each one with <LFD> so that it will be evaluated.
The result is a complete typescript of the expressions you have
evaluated and their values.

   The rationale for this feature is that Emacs must have a buffer when
it starts up, but that buffer is not useful for editing files since a
new buffer is made for every file that you visit.  The Lisp interpreter
typescript is the most useful thing I can think of for the initial
buffer to do.  `M-x lisp-interaction-mode' will put any buffer in Lisp
Interaction mode.