20

Windows 10, Emacs 25.1

I want to do some arithmetic operation I do this: enter image description here

The result is in the echo area, but I want the result to be in cursor place in the buffer. Something like this:

enter image description here

How do I do this?

Drew
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user8542613
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  • Is that supposed to be a "won't"? If yes, Emacs may be the wrong editor for you... – wasamasa Sep 09 '17 at 12:16
  • Emacs is not wrong editor fo me. I use it many years. Sorry for my English. It's not my native language. – user8542613 Sep 09 '17 at 13:05
  • I have a function in my emacs config that I think I got from the bottom of [this post](https://emacs.wordpress.com/2007/01/17/eval-and-replace-anywhere/). – ShreevatsaR Sep 09 '17 at 17:21
  • If you are in the `*scratch*` buffer, `C-j` will evaluate the expression before the cursor and place the value of the expression in the buffer. – gboffi Sep 09 '17 at 22:47

5 Answers5

23

Short version: yes

Instead of C-x C-e to evaluate the expression, give it a prefix argument. C-u C-x C-e will print the output to the buffer.

How I found this information

You can investigate how Emacs does these things by looking in the manual, or asking Emacs itself.

To see what a particular keybinding does, you can use C-h k (describe-key). You were evaluating the expression with C-x C-e, and you can figure out what that keybinding calls with C-h k C-x C-e. That will display the command's docstring, the first part of which is:

C-x C-e runs the command eval-last-sexp (found in global-map), which is an interactive compiled Lisp function in elisp-mode.el.

It is bound to C-x C-e.

(eval-last-sexp EVAL-LAST-SEXP-ARG-INTERNAL)

Evaluate sexp before point; print value in the echo area. Interactively, with a non - prefix argument, print output into current buffer.

...

I highlighted the key phrase: giving it a prefix argument (C-u) will print the output to the buffer, rather than the echo area.

Dan
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    It's good, but it not enough. If I use command `C-u C-x C-e` the result will be **(* 60 3)180**. But I need only **180** (as in my screenshot). – user8542613 Sep 09 '17 at 13:03
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    @user8542613 : then you will need to write your own command. – Dan Sep 09 '17 at 13:12
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    @user8542613 : I think Drew's answer does exactly what you want. Please consider switching accepted answers. – Dan Sep 09 '17 at 15:12
9

Bind this to some key. 

(defun foo ()
  "Replace sexp before point by result of its evaluation."
  (interactive)
  (let ((result  (pp-to-string (eval (pp-last-sexp) lexical-binding))))
    (delete-region (save-excursion (backward-sexp) (point)) (point))
    (insert result)))
Drew
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5

If you want to do an arithmetic operation and insert the value into the buffer, but don't care where you do the operation, then you can also do C-u M-: and type the operation info the minibuffer.

This blog has

(defun eval-and-replace (value)
  "Evaluate the sexp at point and replace it with its value"
  (interactive (list (eval-last-sexp nil)))
  (kill-sexp -1)
  (insert (format "%S" value)))
icarus
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2

I prefer to do (also complex) computations in Emacs' calc C-x * * and then copy its result in the buffer where my cursor was with y, q closes the calc buffers and I'm back at this location.

Dieter.Wilhelm
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    This is what I use all the time. Also, if you want an algebraic expression, you can do C-x * q, enter an expression, then the answer will be on the kill ring, so you can insert it into the buffer with C-y. – Daniel Doherty Aug 21 '21 at 10:05
0

I had the same wish and hadn't used Emacs in a long while and forgot how to do it :) Very simple and touched on by some above answers with the prefix command C-u

Simply C-u M-: (Eval buffer appears for your function) such as Eval: (- 5 2) and the result of 3 will appear in your buffer cursor location

This is very handy for kbd-macros where you need to manipulate some arithmetic and replace values

Rick G
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  • If you're in `Lisp interaction` buffer mode, like `*scratch*`, `C-j` with pos after last expression parenthesis will evaluate it. Note that such evaluation is postion dependent, so place point where the expression is complete. – Muihlinn Jun 04 '20 at 08:38