When evaluated from a scratch buffer, why does the elisp debugger say that variable "a" is void?
(setq a "b")
(insert a)
The reported error is:
Debugger entered--Lisp error: (void-variable a)
You must have forgotten to do a C-j. With it you also
get the feedback with the result of evaluation inserted into the buffer.
I'd also suggest to use ielm.
UPD
Here's the whole sequence, just in case:
emacs -q - don't want any extra packages to mess up anything
q - you're now in *scratch*
(setq a "b")
C-j - "b" should appear automatically
(insert a)
C-j - bnil should appear automatically
Done. The value of a was inserted, along with nil,
which was the result returned from insert.
Related
How can we get variable value with a string in scheme language as we can achieve this in Common Lisp:
> (defvar s 3)
> S
> (symbol-value (intern "S"))
> 3
I am accessing a parameter of parent function from the closure.
EDIT: I have found this solution, but I can't use eval because it evaluates at top level. Searching for alternatives.
(eval (string->symbol "s"))
EDIT 2: I have found that Common lisp code also try to find symbol in global space. So this question is basically for both Lisps(Common Lisp, Scheme).
Don't do that!
Variables are for when you know the variable at compile time. In that case it is never a string. You can still reason about strings in compile time but your code also needs to have a relation with the name for it to be interesting. When you use eval or other forms that evaluate structure and compile/run data in runtime you are probably not doing it right (but not always. I've in my 20 year career used eval intentionally in production code twice)
If you want to store values you use a data structure. An assoc would mimic a dynamic environment. You can also use a hash with a level indicator if the size is harmless.
You can't do what you want to do and in fact it is a confused thing to want to do.
Here's why what you are trying to do is confused. Consider how a Lisp system for which it was possible to do what you wanted would work. In particular consider something like this:
(define (foo a name)
(let ([b 10])
(display (get-value name))
(* a b)))
Where get-value is meant to be how you get the binding of whatever something is.
So, if I call (foo 10 "b") it should print 10 and return 100.
But wait: b is a compile-time constant in this code. Any compiler worth its salt is going to immediately turn this into
(define (foo a name)
(display (get-value name))
(* a 10))
And now there is no binding of b.
So there are two options here: what you want to work works and it is impossible to ever write a reasonable compiler for Scheme, or what you want to work doesn't work, and it is.
Is it possible to update the program code while it is being interpreted by csi, the Chicken Scheme Interpreter? If so, how?
So that I can interactively change part of the code and immediately see the effects of that changes.
For example, suppose I have written the following program:
(define (loop)
(print "Ciao")
(rest 1)
(loop))
(loop)
(assume (rest 1) has the effect of pausing the program for a second).
If I run this program, trough csi, it prints the string "Ciao" every second. If I change the string "Ciao" into something else, for example into "else", and I save the program code file, then csi continue interpreting the old program code, so I continuously see the string "Ciao". I'd like, in this case, that when I save the modified code with the string "Ciao" replaced by "else", csi continue its interpretation job by looking into the modified file, instead of the old file.
So that I obtain as output some "Ciao" followed by some "else": the "else" start to appear when I replace "Ciao" by "else" in the source code.
In general, the answer is "don't". The way you're supposed to use the REPL is by evaluating piecemeal changes against it, then evaluating a function or two to make sure everything went as expected. Part of this approach is structuring your program so that it can be easily tested in pieces, which implies not automatically starting any infinite loops. In the specific case you're asking about, you could instead write
(define (do-stuff)
(print "Ciao"))
(define (main-loop)
(do-stuff)
(rest 1)
(main-loop))
(define (start) (main-loop))
You can now incrementally develop do-stuff, periodically evaluating new versions to your interpreter and calling them to make sure they work, then eventually calling start once you're confident that it's doing the right thing.
You may get mileage out of this similar question asked about Common Lisp.
As an aside, if you were using Common Lisp and SLIME, you could now do more or less what you proposed:
(defun do-stuff ()
(format t "Ciao~%"))
(defun main-loop ()
(loop (progn (do-stuff)
(sleep 1))))
(main-loop)
Starting that up would start printing Ciao on separate lines in your SLIME REPL. If you changed do-stuff to
(defun do-stuff ()
(format t "else~%"))
then hit it with C-c C-c (the default binding for slime-compile-defun), you'd see your SLIME REPL start printing else lines in-flight.
CL-USER> (main-loop)
Ciao
Ciao
Ciao
; compiling (DEFUN DO-STUFF ...)else
else
else
else
else
else
; Evaluation aborted on NIL. User break.
CL-USER>
I'm not sure how to accomplish the same thing in Scheme, but I'm reasonably sure it's possible.
All that being said, you sometimes want to run a program part of which is an infinite loop. A real world example would be while testing a TCP server of some sort. If you're in such a situation, and your desired workflow is
Write file
Run csi my-file.scm
Edit file
Kill csi
Run csi my-file.scm
goto 3
and you basically just want to automate steps 4 through 6, you'll need an external tool to do it for you. Take a look at entr or hsandbox (the latter doesn't have Scheme support out of the box, but it doesn't look like it would be too hard to add).
There is no common way to make a running program check its source for changes but you there seems to be enough feratures available in Chicken to roll your own:
(use posix)
(use srfi-18)
(define (watch-reload! file)
(define (tsleep n)
(thread-sleep! (seconds->time (+ n (time->seconds (current-time))))))
(define (get-time)
(file-modification-time file))
(thread-start!
(lambda ()
(let loop ((filetime '()))
(let ((newtime (get-time)))
(when (not (equal? filetime newtime))
(load file))
(tsleep 10)
(loop newtime))))))
Now all you have to do is to use watch-reload! instead of load and it will check and reload every 10 seconds if the file has been modified.
If you save when the file is not valid scheme it stops working until you call watch-reload! on it again.
It may be that chicken programmers might have a better solution.
I am using Guile in conjunction with Geiser under Emacs while learning how to program in Scheme. I find it actually a hindrance that Guile drops into a debugger each time I make a typo or enter a wrong piece of code. How can I make Guile more tolerant of my typos/errors and skip the debugger, while using it through Geiser under Emacs?
As I get more advanced in Scheme programming, how would I restore the default behavior or else how can I toggle between having the debugger always start vs start only on demand?
You can set the on-error option to report, and it will simply report the error without dropping you in the debugger (that's the default value, debug); e.g.
scheme#(guile-user)> ,option on-error 'report
scheme#(guile-user)> (/ 1 0)
ERROR: Throw to key `numerical-overflow' with args `("/" "Numerical overflow" #f #f)'.
scheme#(guile-user)>
See: https://www.gnu.org/software/guile/manual/html_node/System-Commands.html
I don't really write a lot of Scheme, but it seems that you can just ignore the debugger.
If you're using lispy to do the
eval with e, you don't even see the REPL window, you just
get messages in the echo area with the result.
If you set (setq geiser-impl--implementation 'guile), and press
e in lispy-mode, it will start a Geiser REPL
automatically (if there isn't a live one) and eval the expression.
I have a text file which has related content/paragraphs in it. Let's say that I Cut/Kill paragraph A from the text. I want to write a function that is invoked in this case and therefore the related paragraph - let's say B - is also removed. A good example would be a document that has citations/references in it. - i.e. whenever you remove that text the citation is also removed - something like what MS Office does. Theoretically I think:
1) I need a hook for Cut - which I can't find the appropriate hook so far
2) A search function with regex probably - to find the related text
3) remove that text
Can you advice me how to proceed? Hints for each step or etc.
It's easy to write functions for such cases:
(defun when-one-kill-one-and-three ()
"If a buffer has a string \"one\", it deletes it.
If in this buffer exists also a string \"three\", it will be killed afterwards. "
(interactive "*")
(save-excursion
(save-restriction
(widen)
(goto-char (point-min))
(while (search-forward "one" nil t 1)
(kill-region (match-beginning 0) (match-end 0))
(when (search-forward "three")
(kill-region (match-beginning 0) (match-end 0)))))))
1) I don't think there is a hook for Cut but you can have advised Cutting (defadvice ..)
2) You should somehow markup your text and find it with search (put a number so you search for that) ..
3) To remove text you can use kill-region I suppose
Quite often I define a ruby symbol (eg. :some_value), then I want to create a method with the same name def some_value.
Unfortunately, the autocompletion(M + /) for the second occurrence of some_value string does not work, being slightly different (:some_value vs some_value).
How can I setup emacs to handle such events?
Assuming that M-/ is bound to dabbrev-expand, you can configure dabbrev-mode to ignore certain prefixes when expanding strings. To make a single colon a prefix to be ignored, type
M-x customize-group
and then
dabbrev
This will take you to the customization page for dabbrev-mode. Go to the point Dabbrev Abbrev Skip Leading Regexp and click on Value menu. From the menu, pick "Regexp".
Now you see a textfield labeled "Regexp: " next to the value menu in which you enter a single colon.
:
Then click on the button State in the next line and choose the value "Save for Future Sessions".
First, my results! I typed :some_crazy_symbol in my model. On a newline, I typed def so, hit M-/ twice, and ended up with
def some_crazy_symbol
end
(Rinari supplied the end.)
I got this to work quite well by using hippie-expand. If you want to test it out, bind hippie-expand to M-/ like so:
(global-set-key (kbd "M-/") 'hippie-expand)
Heres' the documentation. Hippie expand works by trying out a number of different expansions on the current point. These expansions are stored in the hippie-expand-try-functions-list variable. On my system (and be default), this variable is set to:
(try-complete-file-name-partially try-complete-file-name try-expand-all-abbrevs try-expand-list try-expand-line try-expand-dabbrev try-expand-dabbrev-all-buffers try-expand-dabbrev-from-kill try-complete-lisp-symbol-partially try-complete-lisp-symbol)
The minibuffer readout showed that this particular expansion was accomplished using the try-expand-dabbrev function.
Not a direct answer to your question, but you should get more intelligent Ruby autocompletion by using auto complete mode paired with rsense.
If Dabbrev Abbrev Skip Leading Regexp and hippie-expand doesn't do exactly what you want and you've got some elisp skills, you could create a custom function for hippie-expand.
See the section about "substring expansion" on the hippie-expand page on the emacs-wiki. There's a function you could use there you could tailor to customize..
Substring Expansion
When doing lisp programming standard dabbrev is less useful, because Emacs has no namespaces, so in a package symbols begin with the same prefix, therefore the same prefix has to be typed again and again if one wants to complete symbols from the package. As with IswitchBuffers it is much more effective if a unique substring can be typed to get to the desired symbol.
Dabbrev offers nothing in this regard, so I turned to Hippie Expand which I had never used before.
Here’s a function based on hippie expand dabbrev expansion which performs substring expansion:
(defun try-my-dabbrev-substring (old)
(let ((old-fun (symbol-function 'he-dabbrev-search)))
(fset 'he-dabbrev-search (symbol-function 'my-dabbrev-substring-search))
(unwind-protect
(try-expand-dabbrev old)
(fset 'he-dabbrev-search old-fun))))
(defun my-dabbrev-substring-search (pattern &optional reverse limit)
(let ((result ())
(regpat (cond ((not hippie-expand-dabbrev-as-symbol)
(concat (regexp-quote pattern) "\\sw+"))
((eq (char-syntax (aref pattern 0)) ?_)
(concat (regexp-quote pattern) "\\(\\sw\\|\\s_\\)+"))
(t
(concat (regexp-quote pattern)
"\\(\\sw\\|\\s_\\)+")))))
(while (and (not result)
(if reverse
(re-search-backward regpat limit t)
(re-search-forward regpat limit t)))
(setq result (buffer-substring-no-properties (save-excursion
(goto-char (match-beginning 0))
(skip-syntax-backward "w_")
(point))
(match-end 0)))
(if (he-string-member result he-tried-table t)
(setq result nil))) ; ignore if bad prefix or already in table
result))
I figured I'd share the solution I came up with that works for hippie-expand.
To summarize:
(defun hippie-expand-ruby-symbols (orig-fun &rest args)
(if (eq major-mode 'ruby-mode)
(let ((table (make-syntax-table ruby-mode-syntax-table)))
(modify-syntax-entry ?: "." table)
(with-syntax-table table (apply orig-fun args)))
(apply orig-fun args)))
(advice-add 'hippie-expand :around #'hippie-expand-ruby-symbols)
hippie-expand will expand symbols in ruby-mode when : is considered a punctuation character, so this advice creates a temporary syntax table where : is a punctuation character and calls hippie-expand with it.