SBCL generates spurious style warnings about undefined functions. (The functions are defined, just later in the file.) I want to solve this problem once and for all. Fortunately, there is a way to do this:
(declaim (sb-ext:muffle-conditions style-warning))
The downside is that CCL, for obvious reasons, barfs on a program containing the above. I try to solve this problem with a conditional:
(#+sbcl (declaim (sb-ext:muffle-conditions style-warning)))
but now SBCL is unhappy: "illegal function call".
How do you put such a declaim into a portable program?
Note that while the existing answer is right, disabling warnings is not a good practice. In your case, it is probably not necessary.
Common Lisp has a notion of compilation unit, where multiple definitions are grouped together. This gives a chance for the compiler/interpreter to take care of cross-references among functions (an interpreter could collect warnings and keep only those that are not found later, for example).
For example, in file #P"/tmp/foo.pl":
(defun mut-rec-foo (x)
(when (plusp x)
(mut-rec-bar (1- x))))
(defun mut-rec-bar (x)
(print x)
(mut-rec-foo (1- x)))
Do not evaluate anything in the file; instead do:
(compile-file #P"/tmp/foo.pl")
; compiling (DEFUN MUT-REC-FOO ...)
; compiling (DEFUN MUT-REC-BAR ...)
; /tmp/foo.fasl written
; compilation finished in 0:00:00.002
No warning. You can then call (load #P"/tmp/foo.fasl") to have the definitions in your current lisp environment, without warnings.
Typically, ASDF and by extension Quicklisp use COMPILE-FILE, so your problem should disappear as soon as you bundle your files into a system.
You can also do:
(with-compilation-unit ()
(defun mut-rec-foo/bis (x)
(when (plusp x)
(mut-rec-bar/bis (1- x))))
(defun mut-rec-bar/bis (x)
(print x)
(mut-rec-foo/bis (1- x))))
Evaluating the whole block shows no warning for *EVALUATOR-MODE* being both :COMPILE or :INTERPRET.
What you witnessed happens when you evaluate each expression one after the other (or maybe one region after another one). There, the compiler has no way to know that the function already exists. Silencing the warning is the worse option, because you might actually have made an error.
If you know in advance that a function will exist, but not in your compilation unit (maybe it is only defined at runtime), the you can declaim that fact, as follows:
(declaim (ftype function my-function))
The above says that my-function must be assumed to be fbound to an object of type function. You could also give more information by refining what kind of function you claim it to be:
(declaim (ftype (function (number) (values string &optional)) num-to-string))
... for a function that accepts a number and returns exactly one value, a string.
(declaim (ftype (function () nil) forever-loop))
... for a function that accepts nothing and never return a value (loop or signals an error).
Omit the outer pair of parentheses:
#+sbcl (declaim (sb-ext:muffle-conditions style-warning))
As you are using declaim, I assume, that the declaration appears at the top-level of a compilation unit. If you need to group multiple top-level statements, you can wrap them all with a progn (which doesn't change the "top-level"-ness).
The reason SBCL did complain is, that its reader reads
((declaim (sb-ext:muffle-conditions style-warning)))
(as the :SBCL feature is present), which is simply a syntax error. CCL does not complain, because its reader reads
()
which is simply another way to spell nil.
Related
This question is somewhat related to an earlier one on programmatically generating symbol macros. I'm using that function in a convenience macro that throws undefined variable warnings. This macro and function:
(defmacro define-data (d body &optional doc)
(if (and doc (not (stringp doc))) (error "Documentation is not a string"))
`(let* ((d-str (string ',d))
(old-package *package*)
(*package* (if (find-package d-str) ;exists?
(find-package d-str) ;yes, return it
(make-package d-str)))) ;no, make it
;; Should we have an eval-when (:compile-toplevel) here?
(defparameter ,d ,body ,doc)
(export ',d old-package)
(define-column-names ,d)))
(defun define-column-names (d)
(maphash #'(lambda (key index)
(eval `(cl:define-symbol-macro ,key (cl:aref (columns ,d) ,index))))
(ordered-keys-table (slot-value d 'ordered-keys))))
are intended to be like defparameter, but additionally set up a few niceties for the user by defining:
a package with the name of d
a parameter in the current package with the data that will be sucked in by body
symbol-macros in package d for access to the individual data vectors
If I use defparameter from the REPL, and then call define-column-names, all is well. However when using the macro I get:
; in: DEFINE-COLUMN-NAMES FOO
; (DEFINE-COLUMN-NAMES CL-USER::FOO)
;
; caught WARNING:
; undefined variable: CL-USER::FOO
I suspect that this is because the compiler has no way of knowing that FOO will actually be defined when define-symbol-macro is called. Everything works fine, but I don't want the warning to frighten users, so am thinking of suppressing it. I hate suppressing warnings though, so thought I'd come here for a second opinion.
EDIT: I've marked an answer correct because it does correctly answer the question as asked. For an answer to the problem see my comments.
My answer to the 'when to muffle warnings' question in the title is: if it's your own code then never, under any circumstances. If it is someone else's code, then rewrite it not to warn unless you can't.
As to solving the problem I haven't thought about this hard enough, but the problem is that you definitely want the defparameter to be at top-level so the compiler can see it, and it can't really be if it's inside a let. But you can raise it to toplevel trivially since it depends on nothing inside the let.
I am then pretty certain that you want the rest of the macro to happen at compile time, because you definitely want the symbol-macros available at compile-time. So an attempt at the first macro would be (note I've fixed the handling of the docstring: (defparameter foo 1 nil) is bad):
(defmacro define-data (d body &optional doc)
(when (and doc (not (stringp doc)))
(error "Documentation is not a string"))
`(progn
(defparameter ,d ,body ,#(if doc (list doc) '()))
(eval-when (:compile-toplevel :load-toplevel :execute)
(let* ((d-str (string ',d))
(old-package *package*)
(*package* (if (find-package d-str) ;exists?
(find-package d-str) ;yes, return it
(make-package d-str)))) ;no, make it
(export ',d old-package)
(define-column-names ,d)))))
As a side note: although I think the fact that programmatically defining symbol macros is hard because CL left that out for some reason, I think I'd personally use some other approach rather than this, because eval is just so horrid. That's just me however: if you want to do this you do need eval I think (it is very rare that this is true!).
I am not sure exactly how define-columns-names works so I replaced it with a stub function that returns d.
Note also that you can use check-type and should try not injecting symbols in generated code, this introduces potential variable capture that can be avoided with gensym.
As far as I know you cannot use eval-when as suggested by your comment (see Issue EVAL-WHEN-NON-TOP-LEVEL Writeup for details).
But I have no warning if I declare the symbol as being special around the call.
(defmacro define-data (d body &optional doc)
(check-type doc (or null string))
(check-type d symbol)
(let ((d-str (string d)))
(alexandria:with-gensyms (old-package)
`(let* ((,old-package *package*)
(*package* (if (find-package ,d-str) ;exists?
(find-package ,d-str) ;yes, return it
(make-package ,d-str)))) ;no, make it
(defparameter ,d ,body ,doc)
(export ',d ,old-package)
(locally (declare (special ,d))
(define-column-names ,d))))))
It is also a bit strange that you expand into a call to define-column-names, which in turns evaluated a form built at runtime. I think it might be possible to do all you want during macroexpansion time, but as said earlier what you are trying to do is a bit unclear to me. What I have in mind is to replace define-column-names by:
,#(expand-column-names-macros d)
... where expand-column-names-macros builds a list of define-symbol-macro forms.
I've been trying to write a recursive loop in clojure that will print me out the very last number in the list. The point is not that I need to get the last number (for which I'm sure there's a built in function for that) but that I want to better understand recursion and macros in clojure. So I have this macro...
(defmacro loop-do [the-list]
`(if (= (count '~the-list) 1)
(println (first '~the-list))
(loop-do (rest '~the-list))))
But I get a stackoverflow error. What am I doing wrong?
How will people use your macro?
Somewhere, someone will call:
(loop-do list)
As a piece of code, those are only two symbols in a list. The first one is recognized as your macro, and the second one, list, is a symbol that represents a variable that will be bound at runtime. But your macro only knows that this is a symbol.
The same goes for:
(loop-do (compute-something))
The argument is a form, but you do not want to get the last element of that form, only the last element of the list obtained after evaluating the code.
So: you only know that in your macro, the-list will be bound to an expression that, at runtime, will have to be a list. You cannot use the-list as-if it was a list itself: neither (count 'list) nor (count '(compute-something)) does what you want.
You could expand into (count list) or (count (compute-something)), though, but the result would only be computed at runtime. The job of the macro is only to produce code.
Recursive macros
Macros are not recursive: they expand into recursive calls.
(and a b c)
might expand as:
(let [a0 a] (if a0 a0 (and b c)))
The macroexpansion process is a fixpoint that should terminate, but the macro does not call itself (what would that mean, would you expand the code while defining the macro?). A macro that is "recursive" as-in "expands into recursive invocations" should have a base case where it does not expand into itself (independently of what will, or will not, happen at runtime).
(loop-do x)
... will be replaced by:
(loop-do (rest 'x))
... and that will be expanded again.
That's why the comments say the size actually grows, and that's why you have a stackoverflow error: macroexpansion never finds a fixpoint.
Debugging macros
You have a stackoverflow error. How do you debug that?
Use macroexpand-1, which only performs one pass of macroexpansion:
(macroexpand-1 '(loop-do x))
=> (if (clojure.core/= (clojure.core/count (quote x)) 1)
(clojure.core/println (clojure.core/first (quote x)))
(user/loop-do (clojure.core/rest (quote x))))
You can see that the generated code still contains a call to usr/loop-do , but that the argument is (clojure.core/rest (quote x)). That's the symptom you should be looking for.
I'm reviving an old LISP program from the early 1980s.
(It's the Nelson-Oppen simplifier, an early proof system.
This version was part of the Ford Pascal-F Verifier,
and was running in Franz LISP in 1982.) Here's
the entire program:
https://github.com/John-Nagle/pasv/tree/master/src/CPC4
I'm converting the code to run under clisp on Linux,
and need some advice. Most of the problems are with
macros.
HUNKSHELL
Hunkshell was a 1970s Stanford SAIL hack to support records with named fields in LISP. I think I've converted this OK; it seems to work.
https://github.com/John-Nagle/pasv/blob/master/src/CPC4/hunkshell.l
The original macro generated more macros as record update functions.
I'm generating defuns. Is there any reason to generate macros?
By the way, look at what I wrote for "CONCAT". Is there a better way
to do that?
DEFMAC
More old SAIL macros, to make macro definition easier before defmacro became part of the language.
https://github.com/John-Nagle/pasv/blob/master/src/CPC4/defmac.l
I've been struggling with "defunobj". Here's my CL version, partly converted:
; This macro works just like defun, except that both the value and the
; function-binding of the symbol being defined are set to the function
; being defined. Therefore, after (defunobj f ...), (f ...) calls the
; defined function, whereas f evaluates to the function itself.
;
(defmacro defunobj (fname args &rest b)
`(progn
(defun ,fname ,args ,b)
;;;;(declare (special ,fname)) ;;;; ***declare not allowed here
(setq ,fname (getd ',fname))))
If I made that declare a proclaim, would that work right?
And what replaces getd to get a function pointer?
SPECIAL
There are lots of (DECLARE (SPECIAL FOO)) declarations at top
level in this code. That's not allowed in CL. Is it
appropriate to use (PROCLAIM (SPECIAL FOO)) instead?
Concat
Essentially correct, but indentation is broken (like everywhere else - I suggest Emacs to fix it).
Also, you don't need the values there.
defunobj
I suggest defparameter instead
of setq. Generally speaking, before setting a variable (with, e.g., setq) one should establish it (with, e.g., let or defvar).
fdefinition is what
you are looking for instead of getd.
I also don't think you are using backquote right:
(defmacro defunobj (fname &body body)
`(progn
(defun ,fname ,#body)
(defparameter ,fname (fdefinition ',fname))))
Special
I think defvar and defparameter
are better than proclaim
special.
PS. Are you aware of the CR.se site?
I use packages a lot and the exported symbols often change their names. When I try to recompile the package I get warnings like this:
package.lisp:3:1:
warning:
MY-PROJECT also exports the following symbols:
(OLD-SYMBOL1 OLD-SYMBOL2 OLD-SYMBOL3)
See also:
Common Lisp Hyperspec, DEFPACKAGE [:macro]
SBCL Manual, *ON-PACKAGE-VARIANCE* [:variable]
--> EVAL-WHEN
==>
(SB-IMPL::%DEFPACKAGE "MY-PACKAGE" '("KE") 'NIL 'NIL 'NIL '("CL") 'NIL
'NIL '("NEW-EXPORTED-SYMBOL1" "NEW-EXPORTED-SYMBOL2") '("MY-PROJECT") 'NIL
...)
I know that I can use (unintern 'old-symbol1) to signal the system I don't want to use that symbol anymore. However this is becoming very tedious when there is a lot of renaming.
My questions are:
1) Is is possible to signal to sbcl or emacs to unintern the old/previously exported symbols automatically?
2) If not - is it possible to get all "old" symbols in a variable?
My plan for 2) is to make a key binding to something like (apply #'unintern *old-symbols*)
Setting the variable *on-package-variance* to a list (:error t) will give you an error instead of a warning when redefining the package. The error will have a restart DROP-THEM to unexport the symbols.
You can add
(setf *on-package-variance* '(:error t))
to your ~/.sbclrc to have it always set when starting up SBCL.
First I don't think you want to unitern symbols. Unintern removes them from the package. I think you want to unexport them to avoid the warning. You can do that with the following function
(defun unexport-package-symbols (package)
(do-symbols (symbol package)
(destructuring-bind (symbol status)
(find-symbol (symbol-name symbol) package)
(when (eq status :external)
(cl:unexport symbol package)))))
;; It takes a package-designator as an argument.
(unexport-package-symbols "MY-PACKAGE")
I'm new to Lisp and I was reading about an text-generator example in ANSI Common Lisp, Chapter 8. I follow the example and defined a function "see" in the scope of a LET variable "prec",
(let ((prec '|.|))
(defun see (symb)
(let ((pair (assoc symb (gethash prev *words*))))
(if (null pair)
(push (cons symb 1) (gethash prev *words*))
(incf (cdr pair))))
(setf prev symb)))
and saved it into a lisp file.
Then when I returned to REPL and tried to invoke see after loading the compiled version of the file, an error occurred:
The variable PREV is unbound.
[Condition of type UNBOUND-VARIABLE]
How do I invoke see properly? And what's a lexical closure for? I'm all confused.
Thanks for helping.
Looks like you've typed prec instead of prev in the enclosing let form.
Lexical closures are functions that 'close over' a part of the lexical environment (hence the name). There are many good introductions to closures in lisp that I will not attempt to repeat here but, essentially, let is the most common way to manipulate the lexical environment; in this case, you want to add the binding for prev, which will then be available to code within the body of the form. Your function see will 'close over' this binding, and so each call to see has access to it, even though when you make these calls, you will no longer be in the lexical environment established by the let form. You could say the function definition takes the binding with it, in a sense.
As you appear to have mis-typed the name of the prev, your function is trying to refer to a binding that has not been established at that point in the code.