evaluate simple elisp buffer in emacs without ielm mode

Question

I have a simple elisp script as below, which I want to run using emacs.

(defun add-numbers (a b)
  (+ a b))

(add-numbers 2 3)

Alternatively, I can goto ielm mode and define the function once and then call from ELSIP console.

I need a way to simply execute the script. I feel like there's some keys to make it execute, most probably c-x c-e but not being able make it work.

I get following error on C-x C-e, it seems a weird debugger mode though.

Debugger entered--Lisp error: (void-variable a)
  eval(a nil)
  eval-last-sexp-1(nil)
  eval-last-sexp(nil)
  call-interactively(eval-last-sexp nil nil)
  command-execute(eval-last-sexp)

Useful reference

EvaluatingExpressions

duthen · Accepted Answer · 2016-05-01 09:39:08Z

3

I would suggest you to try C-h k C-x C-e to rtfm.

As your cursor (the "point", in emacs terminology) is just after the symbol a, the last expression is a.

As the variable a is not bound, trying to evaluate it produces the message error: (void-variable a).

If you really want to use C-x C-e, you should click just after the parenthesis closing the defun call and type C-x C-e and then move the point after the second expression and type again C-x C-e.

If you want to "execute the script" (in emacs terminology, we would say "evaluate the buffer"), you should type M-x eval-buffer RET or Menu > Evaluate buffer.

In this case, all the expressions contained in the buffer are evaluated, but there is no visible output: in you case, the interpreter will evaluate (defun add-numbers (a b) (+ a b)) which will define the function add-numbers (with no output). Then the interpreter will evaluate the expression (add-numbers 2 3) which computes and returns 5, but this does not produce any output.

Try to put in your file

(message "result of %s is %d" '(add-numbers 2 3) (add-numbers 2 3))

and M-x eval-buffer RET again. You should get the message in the minibuffer result of (add-numbers 2 3) is 5.

If you put more than one message in your buffer, you can see all of them with the shortcut C-h e (or M-x view-echo-area-messages RET).

edited May 1, 2016 at 9:39

answered Mar 28, 2016 at 13:29

duthen

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2 Comments

prayagupadhyay Over a year ago

Great. I got it working by C-x C-e twice once at function and once while invoking. But interested in M-x eval-buffer. It does nothing though.

duthen Over a year ago

When you do M-x eval-buffer RET, it does NOT do nothing! It evaluates the whole contents of the buffer. In your case, it defines the function add-numbers. You can verify this assertion using a fresh new emacs, where you try M-: (add-numbers 1 2) RET => you'll get an error (void-function add-numbers). Maybe you'll have to quit the debugger (with the letter q). Then you go to your buffer and do M-x eval-buffer RET and try again M-: (add-numbers 1 2) RET. This time, you'll get the result 3 in the minibuffer, which is the proof that eval-buffer has defined the function!

user5920214 · Accepted Answer · 2016-03-28 11:25:50Z

1

You want eval-defun, which is usually C-M-x. Despite its name, what it does is look for the current top-level form and evaluate that. 'Current' is defined in some way so it does what you expect.

answered Mar 28, 2016 at 11:25

user5920214

Comments

CantrianBear · Accepted Answer · 2016-03-28 13:44:51Z

0

You can use C-M-x with the pointer (cursor) somewhere within the function code, or you can use C-x C-e, but with the pointer at the end of the function.

That means, put your pointer after the last closing parenthesis of the function definition and then press C-x C-e and then move the pointer to the end of the function call and press C-x C-e again.

answered Mar 28, 2016 at 13:44

CantrianBear

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