When I do bulk calculations in a scratch buffer, it is annoying to have to delete the actual expressions after they are evaluated (I want them to be deleted on evaluation).


(+ 2 2)

Pressing C-u C-x C-e gives:

(+ 2 2)4

What I want instead is only this (the expression has been removed):


Is there a command that I'm not aware of? I'm curious if there is an easy work around before I write something of my own.

3 Answers 3


Two possibilities that I am aware of.

  1. In the package crux https://github.com/bbatsov/crux there is a function crux-eval-and-replace which does exactly what you are asking for. If you don't want to use the whole package you can just take this function.
(defun crux-eval-and-replace ()
  "Replace the preceding sexp with its value."
  (let ((value (eval (elisp--preceding-sexp))))
    (insert (format "%S" value))))
  1. There is also the package lispy, see https://github.com/abo-abo/lispy that I like very much for editing lisp files. It has a function lispy-eval-and-replace which also does what you want but might be an overkill if you don't want to use the package.
  • it's funny, I pretty much collected my own crux over time. It could have saved me a whole lot of time.
    – A_P
    Commented Feb 19, 2019 at 14:33

Try writing the expression in the minibuffer instead. Using eval-expression with the universal prefix argument inserts the result:

C-u M-: (+ 2 2) RET
  • Not related to the question. I do bulk calculation on thousands of lines in scratch buffer. Typing it out is not an option by any means.
    – A_P
    Commented Feb 20, 2019 at 14:16

Eval and Replace

The solution here is:

  • No need to install any package.
  • Can be tested directly (see below)
  • Extension is possible with Macros (not mentioned here).

I found the best solution mentioned in the article here Eval and Replace

(defun eval-and-replace ()
  "Replace the preceding sexp with its value."
  (condition-case nil
      (prin1 (eval (read (current-kill 0)))
    (error (message "Invalid expression")
           (insert (current-kill 0)))))

How to test

  1. [Optional] Create a buffer like playground.el and put the code mentioned above (In case you want to keep this snippet for the next session).
  2. Then highlight the code above, then M-x: eval-region
  3. You will get the eval-and-replace loaded to your buffer.
  4. Then simply test it on a lisp expression
  • Open another file called test.el
  • put lisp expression such as (+ 3 4)
  • Put the cursor at the end of this express
  • Run M-x: eval-and-replace function that we loaded. demo
  • Why do you say "no need to install any package"? Your recipe requires 3rd-party library playground.el, doesn't it? Maybe your first bullet should be removed?
    – Drew
    Commented May 24, 2023 at 14:13
  • @Drew-san, I apologize for the unclarity of my previous post, I have adjusted. Indeed, you don't need any package, I mentioned these files (playground. el, test. el) for testing purposes only, I hope it is clear by now. Please let me know
    – Dr Neo
    Commented May 24, 2023 at 14:30
  • Yep, clear now; thanks.
    – Drew
    Commented May 24, 2023 at 15:16

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