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Re: redirect eval output to separate buffer in lisp-interaction mode?

From: Pascal J. Bourguignon
Subject: Re: redirect eval output to separate buffer in lisp-interaction mode?
Date: Sun, 20 Jul 2008 23:04:32 +0200
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/22.2 (gnu/linux)

formido <address@hidden> writes:

> How does one redirect evaluation output to a separate buffer in lisp-
> interaction mode? 

> I'm just getting started with emacs, but it's quite
> similar to an AppleScript environment called Smile that I'm very
> familiar with. 

It's the reverse, it's that AppleScript environment that is quite
similar to emacs.  

> By default, you start in an interactive script shell
> there, too, and the first thing I do after a new install is change the
> prefs to redirect output to the "console". Hopefully I can achieve a
> similar effect here, cos it makes incrementally developing a script
> easier, I think.

Normally, emacs "scripts" don't have output.  What they do is to
_edit_ some buffer.

You could use M-x ielm RET to try out emacs lisp expressions in a
separate REPL.

When you edit your emacs code, if you type C-x C-e after an expression
its output goes to the mini-buffer (and to the *Message* buffer).
Isn't it enough for you?  If you type M-x eval-region RET or M-x
eval-buffer RET output goes to the *Message* buffer, isn't it enough?

(You can also type C-u C-x C-e to have the result be inserted at the point).

If you really want what you say you want, you can just do it:

(defvar *emacs-lisp-interaction-output-buffer*
  (lambda () (current-buffer)))

(defun eval-print-last-sexp/output ()
  "Evaluate sexp before point; print value into the buffer indicated
by *emacs-lisp-interaction-output-buffer* ; it may be either a buffer,
or a function returning a buffer.

If `eval-expression-debug-on-error' is non-nil, which is the default,
this command arranges for all errors to enter the debugger.

Note that printing the result is controlled by the variables
`eval-expression-print-length' and `eval-expression-print-level',
which see."
  (let ((expr (preceding-sexp)))
    (let ((standard-output
           (etypecase *emacs-lisp-interaction-output-buffer*
             (buffer    *emacs-lisp-interaction-output-buffer*)
             (function (funcall *emacs-lisp-interaction-output-buffer*)))))
      (with-current-buffer standard-output
        (if (null eval-expression-debug-on-error)
            (eval-last-sexp-print-value (eval expr))
            (let ((value
                   (let ((debug-on-error eval-last-sexp-fake-value))
                     (cons (eval-last-sexp-print-value (eval expr))
              (unless (eq (cdr value) eval-last-sexp-fake-value)
                (setq debug-on-error (cdr value)))
              (car value)))

Then bind this command to your prefered keys, C-j, C-RET, C-x C-e,

(local-set-key (kbd "C-x C-e") 'eval-print-last-sexp/output)

and assign a buffer to *emacs-lisp-interaction-output-buffer*

(setf *emacs-lisp-interaction-output-buffer*
      (get-buffer "output"))

__Pascal Bourguignon__           

READ THIS BEFORE OPENING PACKAGE: According to certain suggested
versions of the Grand Unified Theory, the primary particles
constituting this product may decay to nothingness within the next
four hundred million years.

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