How to invoke an interactive elisp interpreter in Emacs?

Right now I write expressions in the *scratch* buffer and test them by evaluating with C-x C-e. I would really appreciate having an interactive interpreter like SLIME or irb, in which I could test Emacs Lisp expressions.

From stackoverflow

• In the *scratch* buffer, just type C-j to evaluate the expression before point.

• Well, if you're really interested in a literal REPL for emacs it is possible to write one using the -batch mode of emacs:

  (require 'cl)
  
  (defun read-expression ()
    (condition-case
        err
        (read-string "> ")
      (error
       (message "Error reading '%s'" form)
       (message (format "%s" err)))))
  
  (defun read-expression-from-string (str)
    (condition-case
        err
        (read-from-string str)
      (error
       (message "Error parsing '%s'" str)
       (message (format "%s" err))
       nil)))
  
  (defun repl ()
    (loop for expr = (read-string "> ") then (read-expression)
          do
          (let ((form (car (read-expression-from-string expr))))
            (condition-case
                err
                (message " => %s" (eval form))
              (error
               (message "Error evaluating '%s'" form)
               (message (format "%s" err)))))))
  
  (repl)
  

  You can call this from the command line, or, as you seem to want, from within an emacs buffer running a shell:

  kburton@hypothesis:~/projects/elisp$ emacs -batch -l test.el
  Loading 00debian-vars...
  > (defvar x '(lambda (y) (* y 100)))
   => x
  > (funcall x 0.25)
   => 25.0
  > 
  kburton@hypothesis:~/projects/elisp$
  

  Michał Kwiatkowski : This looks more complicated than it should be - running a shell, which runs another emacs in batch mode, which runs the REPL, all inside the main emacs runtime. Anyway, it solves my problem, so thank you for help!

  Michał Kwiatkowski : This REPL implementation doesn't handle multi-line inputs. If you don't end an expression in a single line it gives: Error parsing '(whatever' (end-of-file repl.el) Is there an easy way to fix that?

• Your best bet is the *scratch* buffer. You can make it more like a REPL by first turning on the debugger:

  M-x set-variable debug-on-error t
  

  Then use C-j instead of C-x C-e, which will insert the result of evaluating the expression into the buffer on the line after the expression. Instead of things like command history, * * * and so forth, you just move around the *scratch* buffer and edit.

  If you want things like * * * to work, more like a usual REPL, try ielm.

  M-x ielm
  

• It's easy to start an interactive Lisp session with:

  M-x ielm
  

  You can read more about this feature in the Emacs manual section on "Lisp Interaction"

  Michał Kwiatkowski : Exactly what I was looking for, big thanks!

• To run just one elisp expression you can use M-: shortcut and enter expression in mini-buffer. For other cases you can use scratch buffer

• Eshell is another option for an interactive Elisp interpreter.

  M-x eshell
  

  Not only is it a command shell like bash (or cmd.exe if on Windows) but you can also interactively write and execute Elisp code.

  ~ $ ls
  foo.txt
  bar.txt
  ~ $ (+ 1 1)
  2