I'm writing some util function in my emacs init.el. It seems that two function with same argument name cause some error.
If I change the argument name of one function, everything is ok. But since the argument is local to the function, they should not affect each other.
(defun for-loop (op list-var)
(if (not (eq list-var nil))
(progn
(funcall op (car list-var))
(for-loop op (cdr list-var)))))
(defun append-to-list (list-var element-list)
(let ((op (lambda (item) (add-to-list list-var item))))
(for-loop op element-list)))
(setq list-1 '(1 2 3))
(append-to-list 'list-1 '(4 5 6))
If I change the name 'list-var' in for-loop to some other name, 'anothoer-list-var' eg. everything goes OK, but as the code above, emacs print the stack:
Debugger entered--Lisp error: (wrong-type-argument symbolp (4 5 6))
add-to-list((4 5 6) 4)
(lambda (item) (add-to-list list-var item))(4)
funcall((lambda (item) (add-to-list list-var item)) 4)
(progn (funcall op (car list-var)) (for-loop op (cdr list-var)))
(if (not (eq list-var nil)) (progn (funcall op (car list-var)) (for-loop op (cdr list-var))))
for-loop((lambda (item) (add-to-list list-var item)) (4 5 6))
(let ((op (function (lambda (item) (add-to-list list-var item))))) (for-loop op element-list))
append-to-list(list-1 (4 5 6))
Welcome to the wonderful world of dynamic scoping!
[ The currently active dynamic binding of list-var is the one done by for-loop rather than the one done by append-to-list, since it's closer in the stack, as you can see in the backtrace. ]
First recommendation: don't use add-to-list on local variables, ever (better use push or cl-pusnew instead)!
Second recommendation: add -*- lexical-binding:t -*- somewhere on the first line of your Elisp files, so that they use the saner lexical scoping by default.
Related
In an automated Emacs Lisp --batch/--script script I need to process the command line arguments given to the script.
I've gotten as far as getting the arguments into a list of the the form:
("--aaa=bbb" "--ccc=ddd=eee" "--blah")
Now, I need to convert them to a list of the form:
(("aaa" "bbb") ("ccc" "ddd=eee") ("blah"))
In Python I'd write something like;
output = []
for v in input:
output.append(v[2:].split("=", 1))
But have been unable to convert that code to Emacs Lisp. I found Elisp split-string function to split a string by . character but wasn't able to figure out how to make it only split on the first equals.
I was heading down a route of using (substring "abcdefg" x x) with (search) from the cl package but it felt like there should be a better way? I think also want to use (mapc '<function> input) where function does the v[2:].split("=",1) part.
You can use split-string. See the following code example.
(setq cmd-line '("--aaa=bbb" "--ccc=ddd=eee" "--blah"))
(setq cmd-line (mapcar (lambda (argstr)
(when (string-match "^--" argstr)
(split-string (substring argstr 2) "=")))
cmd-line))
The output is (("aaa" "bbb") ("ccc" "ddd" "eee") ("blah")).
That is not exactly what you want because of "eee". Maybe you can use that and just neglect "eee".
If the "eee" is really a problem a small modification helps:
(setq cmd-line '("--aaa=bbb" "--ccc=ddd=eee" "--blah"))
(setq cmd-line (mapcar (lambda (arg)
(when (string-match "^--" arg)
(setq arg (split-string (substring arg 2) "="))
(if (cdr arg)
(setcdr (cdr arg) nil))
arg))
cmd-line))
The output is:
(("aaa" "bbb") ("ccc" "ddd") ("blah"))
Variant for the new requirement in the question:
(setq cmd-line '("--aaa=bbb" "--ccc=ddd=eee" "--blah"))
(setq cmd-line (mapcar (lambda (arg)
(when (string-match "^--\\([^=]*\\)\\(?:=\\(.*\\)\\)?" arg)
(let ((opt (match-string 1 arg))
(val (match-string 2 arg)))
(if val
(list opt val)
(list opt)))))
cmd-line))
The output is:
(("aaa" "bbb") ("ccc" "ddd=eee") ("blah"))
I don't like how plists are indented in Elisp.
;; current desired Python (for comparison)
;; '(a 1 '(a 1 {'a': 1,
;; b 2 b 2 'b': 2,
;; c 3) c 3) 'c': 3}
Tried on M-x emacs-version 24.3.1, ran emacs -Q, typed the plist and pressed C-x h C-M-\.
This indentation makes sense when it isn't a list:
(mapcar (lambda (x) (x + 1))
'(1 2 3 4))
How do I change formatting settings so that only plists (or, if that's impossible, all quoted lists) have the desired rectangular indentation, but indentation of everything else stays the same? I need this stored locally in an .el file, so that when I edit this file, it is indented as desired, but this behavior doesn't end up anywhere else.
Found it:
(setq lisp-indent-function 'common-lisp-indent-function)
Here's a sample file:
(setq x '(a 1
b 2
c 3))
;;; Local Variables:
;;; lisp-indent-function: common-lisp-indent-function
;;; End:
I'll just dump my whole indentation config here:
(setq lisp-indent-function 'common-lisp-indent-function)
(put 'cl-flet 'common-lisp-indent-function
(get 'flet 'common-lisp-indent-function))
(put 'cl-labels 'common-lisp-indent-function
(get 'labels 'common-lisp-indent-function))
(put 'if 'common-lisp-indent-function 2)
(put 'dotimes-protect 'common-lisp-indent-function
(get 'when 'common-lisp-indent-function))
You can fix this (in my opinion) bug by overriding lisp-indent-function. The original source of the hack was this Github Gist, which was referenced with some more explanation from this Emacs Stack Exchange answer.
However, I was very uncomfortable overriding a core function like this. For one, it's very opaque—how is a reader supposed to tell what is changed? And worse—what if the official definition of lisp-indent-function changed in the future? How would I know that I needed to update my hack?
As a response, I created the library el-patch, which is specifically designed to address this problem. After installing the package, you can override lisp-indent-function as follows:
(el-patch-defun lisp-indent-function (indent-point state)
"This function is the normal value of the variable `lisp-indent-function'.
The function `calculate-lisp-indent' calls this to determine
if the arguments of a Lisp function call should be indented specially.
INDENT-POINT is the position at which the line being indented begins.
Point is located at the point to indent under (for default indentation);
STATE is the `parse-partial-sexp' state for that position.
If the current line is in a call to a Lisp function that has a non-nil
property `lisp-indent-function' (or the deprecated `lisp-indent-hook'),
it specifies how to indent. The property value can be:
* `defun', meaning indent `defun'-style
(this is also the case if there is no property and the function
has a name that begins with \"def\", and three or more arguments);
* an integer N, meaning indent the first N arguments specially
(like ordinary function arguments), and then indent any further
arguments like a body;
* a function to call that returns the indentation (or nil).
`lisp-indent-function' calls this function with the same two arguments
that it itself received.
This function returns either the indentation to use, or nil if the
Lisp function does not specify a special indentation."
(el-patch-let (($cond (and (elt state 2)
(el-patch-wrap 1 1
(or (not (looking-at "\\sw\\|\\s_"))
(looking-at ":")))))
($then (progn
(if (not (> (save-excursion (forward-line 1) (point))
calculate-lisp-indent-last-sexp))
(progn (goto-char calculate-lisp-indent-last-sexp)
(beginning-of-line)
(parse-partial-sexp (point)
calculate-lisp-indent-last-sexp 0 t)))
;; Indent under the list or under the first sexp on the same
;; line as calculate-lisp-indent-last-sexp. Note that first
;; thing on that line has to be complete sexp since we are
;; inside the innermost containing sexp.
(backward-prefix-chars)
(current-column)))
($else (let ((function (buffer-substring (point)
(progn (forward-sexp 1) (point))))
method)
(setq method (or (function-get (intern-soft function)
'lisp-indent-function)
(get (intern-soft function) 'lisp-indent-hook)))
(cond ((or (eq method 'defun)
(and (null method)
(> (length function) 3)
(string-match "\\`def" function)))
(lisp-indent-defform state indent-point))
((integerp method)
(lisp-indent-specform method state
indent-point normal-indent))
(method
(funcall method indent-point state))))))
(let ((normal-indent (current-column))
(el-patch-add
(orig-point (point))))
(goto-char (1+ (elt state 1)))
(parse-partial-sexp (point) calculate-lisp-indent-last-sexp 0 t)
(el-patch-swap
(if $cond
;; car of form doesn't seem to be a symbol
$then
$else)
(cond
;; car of form doesn't seem to be a symbol, or is a keyword
($cond $then)
((and (save-excursion
(goto-char indent-point)
(skip-syntax-forward " ")
(not (looking-at ":")))
(save-excursion
(goto-char orig-point)
(looking-at ":")))
(save-excursion
(goto-char (+ 2 (elt state 1)))
(current-column)))
(t $else))))))
Here is another less heavyweight solution, based on emacsql-fix-vector-indentation. An advice around calculate-lisp-indent is sufficient.
This only works for plists that use keywords as keys, but that covers a majority of plists. To make this work on quoted lists instead, you could change the looking-at regexp to detect the ' or "`", but that will not cover, say, a nested list.
This can further be packaged up into a minor mode if there is a need to turn it off.
(defun my/inside-plist? ()
"Is point situated inside a plist?
We determine a plist to be a list that starts with a keyword."
(let ((start (point)))
(save-excursion
(beginning-of-defun)
(let ((sexp (nth 1 (parse-partial-sexp (point) start))))
(when sexp
(setf (point) sexp)
(looking-at (rx "(" (* (syntax whitespace)) ":")))))))
(define-advice calculate-lisp-indent (:around (func &rest args)
plist)
(if (save-excursion
(beginning-of-line)
(my/inside-plist?))
(let ((lisp-indent-offset 1))
(apply func args))
(apply func args)))
I'm trying to open a file and read through the sexps. If the form has setq in its first position then traverse the rest of the form adding the in the setq form to an alist.
;;; File passwords.el.gpg
(setq twitter-password "Secret"
github-password "Sauce")
My goal is to able to construct an alist from the pairs in the setq forms in teh file. How I even start?
First, I second the recommendation that you store the passwords in an actual alist and, if necessary, set whatever variables you need to based on that.
That aside, here's another solution that tries to break things out a bit. The -partition function is from the dash.el library, which I highly recommend.
You don't really need to "walk" the code, just read it in and check if its car is setq. The remainder of the form should then be alternating symbols and strings, so you simply partition them by 2 and you have your alist. (Note that the "pairs" will be proper lists as opposed to the dotted pairs in Sean's solution).
(defun setq-form-p (form)
(eq (car form) 'setq))
(defun read-file (filename)
(with-temp-buffer
(insert-file-literally filename)
(read (buffer-substring-no-properties 1 (point-max)))))
(defun credential-pairs (form)
(-partition 2 (cdr form)))
(defun read-credentials-alist (filename)
(let ((form (read-file filename)))
(credential-pairs form)))
;; usage:
(read-credentials-alist "passwords.el")
Alternatively, here's how it would work if you already had the passwords in an alist, like so
(defvar *passwords*
'((twitter-password "Secret")
(github-password "Sauce")))
And then wanted to set the variable twitter-password to "Sauce" and so on. You would just map over it:
(mapcar #'(lambda (pair)
(let ((name (car pair))
(value (cadr pair)))
(set name value)))
*passwords*)
You can use streams to read in the files (read-from-string) and then do the usual elisp hacking. The below isn't robust, but you get the idea. On a file, pwd.el that has your file, it returns the alist ((github-password . "Sauce") (twitter-password . "Secret"))
(defun readit (file)
"Read file. If it has the form (sexp [VAR VALUE]+), return
an alist of the form ((VAR . VALUE) ...)"
(let* (alist
(sexp-len
(with-temp-buffer
(insert-file-contents file)
(read-from-string (buffer-substring 1 (buffer-size)))))
(sexp (car sexp-len)))
(when (equal (car sexp) 'setq)
(setq sexp (cdr sexp))
(while sexp
(let* ((l (car sexp))
(r (cadr sexp)))
(setq alist (cons (cons l r) alist)
sexp (cddr sexp)))))
alist))
(readit "pwd.el")
I'm trying to branch out and learn lisp. One of the basics would be to implement a simple stack. Everything works but my pop function.
;Returns and removes the first element of the stack
(defun my-pop ()
(let (temp (car *stack*))
(setq *stack* (cdr *stack*))
temp))
This correctly removes the "top" of the stack, but does not return it. Earlier, I had this:
;Returns and removes the first element of the stack
(defun my-pop ()
(print (car *stack*)
(setq *stack* (cdr *stack*)))
But I'd rather return the top.
What am I doing wrong? (I assume this has something to do with scope...)
Nothing to do with scope, it's a syntax problem. The syntax of LET is:
(let ((var1 val1)
(var2 val2)
...)
body)
Additionally, a (varN valN) may be abbreviated to just varN, which is equivalent to (varN nil). So what you wrote is equivalent to:
(let ((temp nil) ; bind TEMP to NIL
(car *stack*)) ; bind CAR to value of *STACK*
(setq *stack* (cdr *stack*))
temp)
You need an extra set of parentheses in your LET-bindings:
(let ((temp (car *stack*)))
(setq *stack* (cdr *stack*))
temp)
You could also use the built-in operator PROG1:
(prog1
(car *stack*)
(setq *stack* (cdr *stack)))
Is there a case where gensym's feature of appending unique numbers to the prefix comes in handy? I don't get why there is gensym when
(let ((str "batman"))
(eq (make-symbol str)
(make-symbol str)))
always returns nil.
GENSYM for example makes debugging generated code slightly easier.
Example:
See this expansion of a LOOP macro. You can see which symbols are the same by looking at their names, even though they are not interned in a package. There are two uninterned temp variables. Different names now make the use clear.
CL-USER 4 > (pprint (macroexpand '(loop for i in '(1 2 3) sum i)))
(BLOCK NIL
(MACROLET ((LOOP-FINISH () '(GO #:|end-loop-1103|)))
(LET ((I NIL) (#:|tail-1106| '(1 2 3)) (#:|by-1107| 'SYSTEM:CDR$CONS))
(LET ((#:|accumulator-1104| 0))
(DECLARE (TYPE NUMBER #:|accumulator-1104|))
(TAGBODY
#:|begin-loop-1102| NIL
(PROGN
(WHEN (OR (ENDP #:|tail-1106|)) (GO #:|end-loop-1103|))
(LET ((#:|temp-1109| (FUNCALL #:|by-1107| #:|tail-1106|))
(#:|temp-1108| (SYSTEM:CAR$CONS #:|tail-1106|)))
(SETQ I #:|temp-1108|)
(SETQ #:|tail-1106| #:|temp-1109|)))
(INCF #:|accumulator-1104| I)
(GO #:|begin-loop-1102|)
#:|end-loop-1103| (RETURN-FROM NIL #:|accumulator-1104|))))))