When reading the constant :hi,
I get the error:
test: Wrong type argument: char-or-string-p, :hi
(defun test ()
:hi "greet"
(insert :hi)
)
(test)
What does it mean? Why is "greet" not the output?
Your Error Message
insert operates on strings or characters, but you gave it a symbol (:hi). Put your cursor on insert and hit C-h f RET (or do C-h f insert RET anywhere) and you will get the description of the function insert in buffer *Help*.
Your Problem
My ESP tells me that you think that :hi "greet" in the beginning of your code should bind variable :hi to value "greet" and then (insert :hi) should call insert on the value of :hi that should be "greet".
This is not the case.
:hi "greet" has no effect whatsoever.
:hi is a keyword, it is always a constant that evaluates to itself and cannot be bound.
To bind a local variable, use let, try C-h f let RET.
Thus your code should be
(def test()
"my function to insert a greeting"
(let ((hi "greet"))
(insert hi)))
Remedy
I urge you to read "An Introduction to Programming in Emacs
Lisp",
you will not regret it.
The best way to do it is in Emacs: C-h i m intro TAB RET.
Related
I wonder if it is possible to tell FORMAT to ignore undefined format directives. I have looked at the pages for FORMAT in the CLHS but I don't see anything.
What I am trying to do is to get FORMAT to ignore ~m in a format string and just output ~m instead of trying to replace it with something. My plan is that at that point I will call another function which knows what to do with with ~m.
I guess a related question is then, is there a way to define a function to handle a format directive which is otherwise not defined?
In anticipation of some questions. (1) I guess a workaround would be to substitute a placeholder for ~m, and then substitute it back in afterwards and keep going. I guess I'll do that if all else fails. (2) I guess another general strategy would be to call the other function first, to handle ~m, then call FORMAT on the result. Unfortunately that other function recognizes some of the same directives, and barfs on others; it doesn't recognize only ~m and ignore everything else.
You can define your own format directive with ~/name/, where name is the name of the function which is called. In your case you would have:
(format t "~/m/" 1)
(defun m (stream n colon-mod at-mod)
(format stream "~a" n)) ; or do something else with n
You still need to change the control string, but you can add a preprocessing step where "~m" is replaced by "~/m/".
I don't think there is a way of doing that portably (implementations may let you do all sorts of magic). I'd write a quote-weird-tildes and dequote-weird-tildes pair of functions and then write code like:
(defun format/qw (control &rest args)
(declare (dynamic-extent args)
(type string control)) ;can't be a function
(dequote-weird-tildes
(apply #'format nil (quote-weird-tildes control) args)))
Now you have a function which looks like (format nil ...) and is no harder to use than that. For extra value the quoting and dequoting functions should not cons a string if they don't have to.
From http://www.lispworks.com/documentation/lw50/CLHS/Body/22_c.htm
The control-string argument to format is actually a format control.
That is, it can be either a format string or a function, for example a
function returned by the formatter macro.
So you can do:
(defmacro frmt (control-string)
(let ((str (cl-ppcre:regex-replace-all "~m" control-string "~~m")))
`(formatter ,str)))
Now:
(format t (frmt "~m~A") 1)
outputs:
~m1
NIL
This way you don't have to modify the control string directly.
You do have to modify the call to format to include frmt.
I'm not sure if the question title is appropriate but here is what I wonder:
From the repl, I wanted to get the list of bindings defined in the current module. After some searching this seemed like a good solution:
(define (racket-symbols-set)
(list->set (namespace-mapped-symbols (module->namespace 'racket))))
(define (namespace-symbols-set)
(list->set (namespace-mapped-symbols)))
(define (module-bindings)
(set->list (set-subtract
(namespace-symbols-set)
(racket-symbols-set))))
so, calling (module-bindings) returns a list of symbols. But if I try to call a symbol from that result, such as doing ((first (module-bindings))), I get a "application: not a procedure" error although the first symbol is a procedure.
How do I call the corresponding procedure of that symbol?
You can look up the value of a namespace variable using namespace-variable-value. And since your namespace-symbols-set just uses the current namespace, which is also the default namespace for namespace-variable-value, using it is very simple.
For example, to invoke the procedure associated with the first item in the list returned by your module-bindings procedure:
((namespace-variable-value (car (module-bindings))))
Alternatively, specify your preferred namespace as the fourth argument of the namespace-variable-value call.
You need to evaluate that symbol in order for it to return the corresponding procedure.
> (define (foo) 'bar)
> (eval 'foo)
#<procedure:foo>
> ((eval 'foo))
'bar
Hence in your case
((eval (car (module-bindings))))
will call the first procedure of the list returned by module-bindings.
Here is a short elisp code which shows that the behaviour of a function depends on the name of its variable. Is this a bug?
A function is declared using a variable x. When that function is called with a variable named anything other than x, it works as expected. But if it is called with a variable named x, it fails!
My system is GNU Emacs 22.2.1 (powerpc-apple-darwin8.11.0, Carbon Version 1.6.0) of 2008-04-05 on g5.tokyo.stp.isas.jaxa.jp
Paste this on an emacs buffer, put the cursor after the last parehthesis and press \C-x\C-e to see that the function make-zero does now work correctly when called the second time.
(progn
(defun make-zero (x)
"Simple function to make a variable zero."
(set x 0))
(setq x 10)
(insert "\n Variable x is now equal to " (number-to-string x))
(setq y 20)
(insert "\n Variable y is now equal to " (number-to-string y))
(insert "\n\n Let us apply make-zero to y")
(make-zero 'y)
(insert "\n Variable y is now equal to " (number-to-string y))
(insert "\n\n Let us apply make-zero to x")
(make-zero 'x)
(insert "\n Variable x is now equal to " (number-to-string x))
(insert "\n\n Why make-zero had no effect on x? Is it because the name of the
variable in the definition of make-zero, namely 'x', is the same as the name of
the variable when make-zero was called? If you change the name of the variable
in the definition of make-zero from x to z, this strange behaviour will
disappear. This seems to be a bug in elisp."))
It's not a bug so much as the nature of Elisp's (and Lisp in general) dynamic binding. ' doesn't pass a reference (that is, it's not like & in C/C++), it passes an unevaluated symbol; what it then evaluates to depends on the scope in which it's evaluated, which means it gets the x that's in scope inside the function.
In Lisp-think, the normal way around this would be to use a macro.
(defmacro make-zero (x) (list 'set x 0))
or
(require 'cl)
(defmacro make-zero (x) `(set ,x 0))
It's not a bug. It'd be worth your while reading the manual entry for Scoping Rules For Variable Bindings.
The function you wrote calls set, which takes a symbol (the value of the first argument) and changes its value to the value of the 2nd argument. The make-zero you wrote binds x locally to its input argument, so when you pass in the symbol x, set changes the first binding for x it finds, which happens to be the local binding.
Here's a different example, let's say you just had the following:
(defun print-something (something)
(set 'something "NEW VALUE")
(insert something))
(print-something "OLD") ; inserts "NEW VALUE"
Looking at that snippet of code, does it make sense that the set line changes the local value of something?
It doesn't matter whether or not there's a global setting for the symbol something.
Another example is the following:
(defvar x "some global value") ;# could have used setq here
(let ((x "local binding"))
(set 'x "new value"))
Which binding would you expect the set line to change? The one created by the let or the global one created by defvar?
The function you wrote is (pretty much) doing exactly the same thing as the let, you're creating a local binding for a variable which is seen before the global one.
If you want to pass around a reference to a variable then the only safe way to do that is via macros, which I recommend, but not until you've grasped the basics of lisp (b/c macros are definitely more complicated). That said, don't let me stop you from diving into macros if that's your passion.
A good introduction to programming Emacs lisp can be found here.
geekosaur's answer does a nice job of showing how you'd achieve what you want.
I have written function (actually a macro, but whatever) that works similarly to progn. How can I tell emacs that this function should be indented in the same way as progn?
This should do it
(put 'myfunc 'lisp-indent-function 0)
Documentation for lisp-indent-function (found by C-h f lisp-indent-function RET):
lisp-indent-function is a compiled Lisp function in `lisp-mode.el'.
(lisp-indent-function indent-point state)
This function is the normal value of the variable
`lisp-indent-function`. It is used when indenting a line within
a function call, to see if the called function says anything
special about how to indent the line.
indent-point is the position where the user typed TAB, or
equivalent. 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 which has
a non-nil property `lisp-indent-function`, that specifies how
to do the indentation. The property value can be:
* `defun`, meaning indent `defun`-style;
* 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 just as this function was called. If that
function returns nil, that means it doesn't specify
the indentation.
This function also returns nil meaning don't specify the
indentation.
As it's "actually a macro":
C-hig (elisp) Indenting Macros RET
In this instance:
(defmacro my-macro (&rest body)
"Does things"
(declare (indent defun))
`(progn ,#body))
(my-macro
(message "foo")
(message "bar"))
How do I disable all warnings in sbcl? The extra output is rather annoying.
After much faffing about
and slogging through documentation written by people who are apparently allergic to simple concrete examples
(which seems to be most documentation for most things)
I think all you need to do to disable all warnings
is add this line in your .sbclrc file:
(declaim (sb-ext:muffle-conditions cl:warning))
To disable only style-warnings, it's:
(declaim (sb-ext:muffle-conditions cl:style-warning))
I tried to disable specifically the warning that comes up if you enter eg (setq x 1) at a fresh REPL
; in: SETQ X
; (SETQ X 1)
;
; caught WARNING:
; undefined variable: X
;
; compilation unit finished
; Undefined variable:
; X
; caught 1 WARNING condition
By using this:
(declaim (sb-ext:muffle-conditions sb-kernel:redefinition-warning))
but it didn't work,
(apparently redefinition-warning means something else)
and I can't find what it should be.
I guessed sb-kernel:undefined-warning
but that doesn't exist.
Using a macro
Also,
in regards #Bogatyr's answer
(using a macro to automatically run defvar)
and #spacebat's comment
(that the macro evaluated the value twice)
I have this to say:
As another newb coming across this,
I wanted to make demo showing that the macro evals twice,
and showing a version that evaluates only once.
(
I originally edited it in at the end of the question
but it was rejected because:
"This edit was intended to address the author of the post and makes no sense as an edit. It should have been written as a comment or an answer."
Well, you can't answer an answer,
but comments can't take blocks of code,
so I guess I should put it here instead?
)
original
(defmacro sq (var value)
`(progn
(defvar ,var ,value)
(setq ,var ,value)))
(sq v (princ "hi"))
side-effects: prints hihi
return value: "hi"
rewrite 2 - only evals once, always runs defvar
(defmacro sq2 (var value)
(let
((value-to-set value))
`(progn
(defvar ,var)
(setq ,var ,value-to-set))))
(sq2 v (princ "hi"))
side-effects: prints hi
return value: "hi"
rewrite 3 - same as above, but trickier to read
I used value-to-set for clarity,
but you could just use value again with no problems:
(defmacro sq3 (var value)
(let
((value value))
`(progn
(defvar ,var)
(setq ,var ,value))))
(sq3 v (princ "hi"))
rewrite 4 - only runs defvar if the variable is unbound
Running those macros will always define the variable before setting it,
so if v was already "bound" but not "defined"
(ie you had introduced it with setq)
then won't get any more error messages when you use the variable,
or reset it with setq.
Here's a version of the macro
that only runs defvar if the variable is not already bound:
(defmacro sq4 (var value)
(let
((value-to-set value))
(if (boundp var)
`(setq ,var ,value-to-set)
`(progn
(defvar ,var)
(setq ,var ,value-to-set)))))
(sq4 v (princ "hi"))
So if you use it to set a variable that is bound but not defined
it will keep giving you error messages.
(Which is maybe a good thing?
Like, for the same reason-I-don't-actually-know-why the error message exists in the first place.)
[
Also,
I tested the macro on these:
(sq4 value 1 )
(sq4 value 'value )
(sq4 value 'value-to-set )
(sq4 value 'var )
(sq4 value-to-set 1 )
(sq4 value-to-set 'value )
(sq4 value-to-set 'value-to-set )
(sq4 value-to-set 'var )
(sq4 var 1 )
(sq4 var 'value )
(sq4 var 'value-to-set )
(sq4 var 'var )
(You know, checking I hadn't screwed up and... done something weird.)
The ones where I tried to use var as a variable spewed errors.
At first I thought I had messed something up,
but it's actually just reserved for something special in SBCL(?) itself.
(defvar var) gets:
; debugger invoked on a SYMBOL-PACKAGE-LOCKED-ERROR in thread
; #<THREAD "main thread" RUNNING {AB5D0A1}>:
; Lock on package SB-DEBUG violated when globally declaring VAR SPECIAL while
; in package COMMON-LISP-USER.
; See also:
; The SBCL Manual, Node "Package Locks"
So... when in doubt, avoid using the symbol var, I guess.
]
this is what i use to muffle both compile-time and runtime (load-time) redefinition warnings:
(locally
(declare #+sbcl(sb-ext:muffle-conditions sb-kernel:redefinition-warning))
(handler-bind
(#+sbcl(sb-kernel:redefinition-warning #'muffle-warning))
;; stuff that emits redefinition-warning's
))
following this pattern you can install these handlers on superclasses like cl:style-warning to muffle all style warnings.
You can either use SB-EXT:MUFFLE-CONDITIONS as Pillsy said, the other alternative is to read through the warnings and use them to modify your code to remove the warnings. Especially if they're actually warnings (rather than, say, optimization notes).
I couldn't get SB-EXT:MUFFLE-CONDITIONS to work for the highly annoying undefined variable warning even after much googling. That warning drives me nuts when experimenting at the REPL, so I did what all the books suggest we should do: extend lisp to suit my needs/preferences!
I wrote my own setq that shut up the sbcl warnings, my first macro ever :). I'm sure there are better ways to do it but this works great for me, and it's going right into my ~/.sbclrc!
(defmacro sq (var value)
`(progn
(defvar ,var ,value)
(setq ,var ,value)))
You probably want to look at SB-EXT:MUFFLE-CONDITIONS.
If warnings are all you care about you can set:
(setf sb-ext:*muffled-warnings* 'style-warning)
This will only apply to style warnings and allow other warnings and conditions to print out. Any warning that shares the same parent will be automatically muffled.
For me (and probably others), most of the warnings were actually being piped to stdErr.
So this silenced the annoying output:
sbcl 2>/dev/null/
Alternatively, you can pipe to a file.
sbcl 2>myTempLog.txt
When starting sbcl, the problem is that at least in my configuration, alexandria spews out a tonne of method warnings and redifining warnings because of asdf, alexandria and readline, regardless of the mute solutions.
User theoski's solutions (sbcl 2>/dev/null ...) totally work to get rid of those, but at the expense of warnings that might actually be useful.
Still, I always have a repl open in a terminal as a scratch for quick hacks and experimenting, and it's a LOT nicer not seeing that avalanche when loading it up.