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
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).
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.
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.
Related
I am an hour new into programming in Emacs lisp. I have a little experience with scheme so I understand the big picture of lisps in general. However, I have only used the "pure functional" subset of scheme and do not know how to do practical tasks.
Write now, I know that C-x C-e will evaluate the code enclosed by the parentheses' by the current cursor position.
I wish to loop from i = 1 to 10 and print the values of i out. How is this done? I tried the following:
(defvar i 1)
(while (< i 11)
(print "i: " i)
(setq i (+ i 1)))
Emacs tells me: invalid function 0.
How do I do this correctly?
Why is emacs telling me invalid function 0
Feel free to give me tips about how to use the scratch buffer (all I know is C-x C-e evaluates) in emacs. Thanks for all the help!
EDIT1: Could someone tell me how to print out sequential values of i using a while loop?
EDIT2: When I evaluate the code, it opens up another tiny buffer showing each value of i one at a time. However, it is not a large buffer and only shows values of i from 13 to 19. When I try to get into that buffer, it closes immediately. How do I "scroll" through that tiny buffer? Note that I use emacs 24.3 through the terminal
EDIT3: I figured out that the tiny buffer is the Messages buffer. Is there a better way to view the output of my elisp code? The Messages buffer is full of other junk from evaluating things in emacs.
First and foremost, enable "Enter debugger on error" from the Options menu now and add (setq debug-on-error t) or (custom-set-variables '(debug-on-error t)) to your ~/.emacs.el.
Then you will get a *Backtrace* buffer on C-x C-e:
Debugger entered--Lisp error: (invalid-function 1)
1(10)
print("i: " 1)
(while (< i 11) (print "i: " i) (setq i (+ i 1)))
eval((while (< i 11) (print "i: " i) (setq i (+ i 1))) nil)
eval-last-sexp-1(nil)
eval-last-sexp(nil)
call-interactively(eval-last-sexp nil nil)
command-execute(eval-last-sexp)
which shows that the error comes from print.
C-h f print RET will tell you why, but the upshot is that you want to use insert instead of print here.
Just as an added note, since you mentioned knowing some scheme -- if you like the interactive REPL that you can use in typical scheme environment, you might like ielm -- I think it probably stands for Interactive Emacs Lisp mode. Not sure. Anyway, M-x ielm RET will open up an emacs lisp REPL. Sometimes it is actually useful -- for example, when you want to inspect the content of a variable with a lot of data in it, ielm will print the whole thing out. Ielm is built in to my Emacs. Not sure when it was added to the standard distribution, but the earliest copyright in the source says 1994, so it is probably in your Emacs.
You can evaluate Emacs-Lisp sexps in *scratch* or in any other buffer in the same mode or (my preference) in mode emacs-lisp-mode.
In *scratch* you need only hit C-j (newline) after a sexp to evaluate it. In an emacs-lisp-mode buffer you can, as you said, use C-x C-e after a sexp. Or you can use M-x evaluate-region after selecting one or more sexps. As always, C-h m in any mode tells you about it, and usually lists important key bindings.
You can also check a global variable value using C-h v SOME-VAR. And you can evaluate any sexp on the fly from the minibuffer, using M-:. For example: M-: (setq foo (+ 42 (length bar)))
Wrt the debugger:
As #sds mentioned, debug-on-error puts you in the debugger when an error is raised. You can also set debug-on-quit and then enter the debugger using C-g to quit (e.g., during a loop).
If you know the function you want to debug, you can use M-x debug-on-entry.
Step through the debugger using d, or skip to the end of a step using c. Use q to quit the debugger.
You can also insert calls to function debug in source code, as debugger entry points: (debug).
The backtrace in the debugger is always more informative if you load the relevant source file e.g., foo.el, instead of the byte-compiled file, e.g., foo.elc. So before you use M-x debug-on-entry use C-h f to find out which file the function is defined in, and then load that file using M-x load-file /path/to/the/file.el.
There is also another debugger, besides debug -- look for edebug in the Elisp manual. Some people prefer edebug; I prefer debug.
I have never written an emacs function before and was wondering if anyone could help me get started. I would like to have a function that takes a highlighted region parses it (by ",") then evaluates each chunk with another function already built into emacs.
The highlighted code may look something like this: x <- function(w=NULL,y=1,z=20){} (r code), and I would like to scrape out w=NULL, y=1, and z=20 then pass each one a function already included with emacs. Any suggestions on how to get started?
A lisp function is defined using defun (you really should read the elisp intro, it will save you a lot of time - "a pint of sweat saves a gallon of blood").
To turn a mere function into an interactive command (which can be called using M-x or bound to a key), you use interactive.
To pass the region (selection) to the function, you use the "r" code:
(defun my-command (beg end)
"Operate on each word in the region."
(interactive "r")
(mapc #'the-emacs-function-you-want-to-call-on-each-arg
;; split the string on any sequence of spaces and commas
(split-string (buffer-substring-no-properties beg end) "[ ,]+")))
Now, copy the form above to the *scratch* emacs buffer, place the point (cursor) on a function, say, mapc or split-string, then hit C-h f RET and you will see a *Help* buffer explaining what the function does.
You can evaluate the function definition by hitting C-M-x while the point is on it (don't forget to replace the-emacs-function-you-want-to-call-on-each-arg with something meaningful), and then test is by selecting w=NULL,y=1,z=20 and hitting M-x my-command RET.
Incidentally, C-h f my-command RET will now show Operate on each word in the region in the *Help* buffer.
I'm just starting to learn emacs (woohoo!) and I've been mucking around in my .emacs quite happily. Unfortunately, I don't know Lisp yet, so I'm having issues with the basics.
I've already remapped a few keys until I fix my muscle memory:
(global-set-key (kbd "<f9>") 'recompile)
That's fine. But how can I tell a key to 'simulate pressing several keys'? For instance, I don't know, make <f1> do the same as C-u 2 C-x } (widen buffer by two chars).
One way is to look up that C-x } calls shrink-window-horizontally, and do some sort of lambda thing. This is of course the neat and elegant way (how do you do this?). But surely there's a way to define <f1> to send the keystrokes C-u 2 C-x }?
Sure there is, and it's the obvious way:
(global-set-key (kbd "<f1>") (kbd "C-u 2 C-x }"))
For anything long-term, I would recommend the approach shown by seh, as that will naturally be more robust in most situations. It requires a little more work and know-how, of course, but it's all worthwhile :)
angus' approach is like a cut-down version of the keyboard macros feature that gives Emacs its name (and slightly simpler to use than macros for the example in question). You should definitely be aware of macros, however -- they can be exceedingly useful, and for anything more complicated it quickly becomes far easier to record one dynamically than to write out all the individual keys manually.
Here's the summary I wrote myself of the most important bits:
;;;; * Keyboard macros
;; C-x ( or F3 Begin recording.
;; F3 Insert counter (if recording has already commenced).
;; C-u <n> C-x ( or F3 Begin recording with an initial counter value <n>.
;; C-x ) or F4 End recording.
;; C-u <n> C-x ) or F4 End recording, then execute the macro <n>-1 times.
;; C-x e or F4 Execute the last recorded keyboard macro.
;; e or F4 Additional e or F4 presses repeat the macro.
;; C-u <n> C-x e or F4 Execute the last recorded keyboard macro <n> times.
;; C-x C-k r Apply the last macro to each line of the region.
;; C-x C-k e Edit a keyboard macro (RET for most recent).
;; C-x C-k b Set a key-binding.
;;
;; If you find yourself using lots of macros, you can even name them
;; for later use, and save them to your init file.
;; M-x name-last-kbd-macro RET (name) RET
;; M-x insert-kbd-macro RET (name) RET
;;
;; For more documentation:
;; C-h k C-x (
;; M-: (info "(emacs) Keyboard Macros") RET
If we play with the example from the question, you'll see how some of these things tie together...
To begin with, you can define the macro with F3C-u2C-x}F4
You could then bind it temporarily to F1 with C-xC-kbF1 (actually that's not true if F1 is currently a prefix key for an existing keymap, as typing it interactively will simply prompt for the remainder. You can circumvent this in code with (global-set-key (kbd "<f1>") ...), but I would suggest sticking to the reserved bindings).
If you then use describe-key (C-hk) to examine what is bound to that key, Emacs will show you a (lambda) expression which you could copy to your init file if you so wished.
Alternatively, you could name the macro and ask Emacs to insert the code into the current buffer:
M-x name-last-kbd-macro RET (name) RET
M-x insert-kbd-macro RETRET
This code will look different to the lambda expression shown by describe-key, but if you evaluate the inserted macro, you'll see the equivalence. You can likewise show that the (kbd "...") expression also evaluates to the same value, and therefore these are all just alternative ways of doing the same thing.
(You can use the *scratch* buffer to evaluate the code by moving point after the end of the expression, and either typing C-xC-e to show the value in the minibuffer, or C-j to insert the value into the buffer).
Note that the 'inserted' code uses fset to assign the macro to a symbol. You could bind the macro to a key either by executing the (fset) and then assigning that symbol to a key with (global-set-key), or you could ignore the (fset) and simply assign the macro value directly. This, of course, is directly equivalent to angus' answer.
Edit: I've just noticed that there's a kmacro-name-last-macro function bound to C-xC-kn which is nearly identical in form to name-last-kbd-macro, but which generates the lambda expression form seen when using kmacro-bind-to-key (C-xC-kb) and describe-key.
I'll use shrink-window-horizontally as the example function, but you can generalize the idea to any bindings you'd like to define.
If you want to use two as the default amount to shrink the window, rather than one, try the following:
(global-set-key [f9]
(lambda (&optional n)
(interactive "P")
(shrink-window-horizontally (or n 2))))
That binds the F9 key to an interactive function accepting a prefix argument. If you just press F9, you'll pass no argument, which summons the default value of 2, as the parameter n will receive nil as an argument. However, if you press, say, C-u 10 F9, you'll pass ten as the argument for n. This allows you to use your binding more flexibly.
general-simulate-key from general.el works better (in my case a sequence with popups and changing keymaps that I couldn't get to work with macros): https://github.com/noctuid/general.el#simulating-keypresses
Let's say I have the following line in .emacs file.
(setq-default default-directory "~/Desktop/mag")
How can I check the value for `default-directory' in elisp?
Added
I asked this question as I need to check the value of default-directory based on this question.
The elisp code should change the default directory when I click C-x C-f, but I still get ~/, not ~/Desktop/mag. So, I need to check what value the default-directory has.
If you're at the console you can type C-h v, which will prompt you for a variable name. Type in default-directory (or any other name) and you'll get a buffer with some info about that variable, including its value.
The elisp function you're running is describe-variable:
(describe-variable VARIABLE)
I figured this out by C-h k C-h v. C-h k shows you what function the next key or key sequence would call.
If you just want to check the value, you can run the following from the *scratch* buffer:
(print default-directory) <ctrl-j>
The *scratch* buffer allows you to evaluate lisp on the fly. You must hit ctrl-j after to evaluate.
As previously stated, C-h v is the easiest way to find out a variables value. To make it even better, place your cursor on the variable you want to know about, and then run C-h v, and it will default to the word under the cursor. Really handy.
Try:
(print default-directory)
write the above code in one line inside of emacs, got to the end of the line and hit C-x C-e
If you just want to see the variable value in the echo
area (less of a mess), try:
(defun describe-variable-short (var)
(interactive "vVariable: ")
(message (format "%s: %s" (symbol-name var) (symbol-value var))) )
(global-set-key "\C-hV" 'describe-variable-short)
Is there a way to convert an emacs macro into elisp, not like what M-x insert-kbd-macro does, the actual activity becoming elisp statements.
Thanks for your help.
Nope, sorry. There is no trivial way to convert an emacs macro into elisp.
Update: There's been some work on Emacs to start down this path. See this thread as a starting point. It's still not possible (June 2010), but there's activity.
The first reason I can think of is dealing with interactive commands and translating keystrokes into proper arguments for functions.
Think of the following sequence:
C-x b .em TAB RET
This begins the command to switch to a buffer, types three characters, uses TAB completion to complete it and RET to accept. The equivalent lisp for the end result (in an emacs session where the TAB completion is unique) is:
(switch-to-buffer ".emacs")
Thinking of completion, there are also interactions with expansion of all types (dabbrev, hippie-expand, etc.).
A starting point can be M-x edit-last-kbd-macro which (in my case) shows this:
;; Keyboard Macro Editor. Press C-c C-c to finish; press C-x k RET to cancel.
;; Original keys: C-x b .em <tab> RET
Command: last-kbd-macro
Key: none
Macro:
C-x b ;; switch-to-buffer
.em ;; self-insert-command * 3
<tab> ;; pabbrev-expand-maybe
RET ;; newline-and-indent
Which at least gives you some of the function names. But you'll see that RET is labeled as 'newline-and-indent which is incorrect because at the time of the macro execution, the minibuffer is active and the binding is in fact 'minibuffer-complete-and-exit. Similarly, the proper binding for TAB is 'minibuffer-complete.
I made a package that allows pretty much exactly this at https://github.com/Silex/elmacro
It has some quirks but it works pretty well... for example, the following macro:
F3 C-e M-b M-u C-a C-n F4
Generates the following elisp:
(defun upcase-last-word ()
"Change me!"
(interactive)
(move-end-of-line 1)
(backward-word 1)
(upcase-word 1)
(move-beginning-of-line 1)
(next-line 1 1))