Common Lisp exporting symbols from packages

问题:

Is there a short way of exporting all the symbols from a package or is it the only way to do it in defpackage. I generally write my code in a file foo.lisp which generally starts with (in-package :foo) and put the package definition to a file package.lisp which generally involves something like this:

(in-package :cl-user)

(defpackage :foo
  (:use :cl)
  (:documentation "Bla bla bla."
  (:export :*global-var-1*
           :*global-var-2*
           :function-1
           :function-2
           :struct
           :struct-accessor-fun-1
           :struct-accessor-fun-2
           :struct-accessor-fun-3
           :struct-accessor-fun-4))

My question is: Designing simply an interface using some global variables and functions may not be adequate sometimes, and you have to export some structures. When this is the case, if you don't simply export accessor functions of this struct, you can not manipulate objects of these struct. So, is there an easy way for accomplishing this effect without manually exporting all these accessor functions?

回答1:

Once the package is created, and all symbols in it created, e.g., by loading your code that implements the package, you can export any symbols you like, e.g., to export all:

(do-all-symbols (sym (find-package :foo)) (export sym))

You'll probably be happier with

(let ((pack (find-package :foo)))
  (do-all-symbols (sym pack) (when (eql (symbol-package sym) pack) (export sym))))

which won't try re-exporting everything from used packages.

回答2:

Evaluating the macroexpanded code, I get an error for the last nil in the defclass form if no class option is supplied and additional errors as the symbols of the export function have to be quoted. Here is a corrected version which seems to work on my common lisp system (sbcl):

(defmacro def-exporting-class (name (&rest superclasses) (&rest slot-specs)
                               &optional class-option)
  (let ((exports (mapcan (lambda (spec)
                           (when (getf (cdr spec) :export)
                             (let ((name (or (getf (cdr spec) :accessor)
                                             (getf (cdr spec) :reader)
                                             (getf (cdr spec) :writer))))
                               (when name (list name)))))
                         slot-specs)))
    `(progn
       (defclass ,name (,@superclasses)
         ,(append 
           (mapcar (lambda (spec)
                     (let ((export-pos (position :export spec)))
                       (if export-pos
                       (append (subseq spec 0 export-pos)
                           (subseq spec (+ 2 export-pos)))
                       spec)))
               slot-specs)
           (when class-option (list class-option))))
       ,@(mapcar (lambda (name) `(export ',name))
                 exports))))


(macroexpand-1
 '(def-exporting-class test1 nil
   ((test-1 :accessor test-1 :export t)
    (test-2 :initform 1 :reader test-2 :export t)
    (test-3 :export t))))

(PROGN
 (DEFCLASS TEST1 NIL
           ((TEST-1 :ACCESSOR TEST-1) (TEST-2 :INITFORM 1 :READER TEST-2)
            (TEST-3)))
 (EXPORT 'TEST-1)
 (EXPORT 'TEST-2))

回答3:

Vsevolod's post inspired me to post a macro as well:

(defmacro defpackage! (package &body options)
  (let* ((classes (mapcan 
                    (lambda (x) 
                      (when (eq (car x) :export-from-classes)
                        (cdr x)))
                    options))
         (class-objs (mapcar #'closer-common-lisp:find-class classes))
         (class-slots (mapcan #'closer-mop:class-slots class-objs))
         (slot-names (mapcar #'closer-mop:slot-definition-name class-slots))
         (slots-with-accessors
           (remove-duplicates (remove-if-not #'fboundp slot-names))))
    (setf options (mapcar
                    (lambda (option)
                      (if (eq (car option) :export)
                        (append option 
                                (mapcar #'symbol-name slots-with-accessors))
                        option))
                    options))
    (setf options (remove-if 
                    (lambda (option)
                      (eq (car option) :export-from-classes))
                    options))
    `(defpackage ,package ,@options)))

To use:

CL-USER> 
(defclass test-class ()
  ((amethod :accessor amethod :initarg :amethod :initform 0)
   (bmethod :reader bmethod :initform 1)))
#<STANDARD-CLASS TEST-CLASS>
CL-USER> 
(closer-mop:ensure-finalized  (find-class 'test-class))
#<STANDARD-CLASS TEST-CLASS>
CL-USER> 
(macroexpand-1 
  `(defpackage! test-package
     (:export "symbol1")
     (:export-from-classes test-class)))
(DEFPACKAGE TEST-PACKAGE
  (:EXPORT "symbol1" "AMETHOD" "BMETHOD"))
T
CL-USER> 

This isn't well tested, and I'm still learning the MOP API, so there may be much better/cleaner ways to achieve the same goal here (especially the fboundp kludge). Also, this only looks for accessor functions on a class. There are also methods that specialize on a class. You could use the MOP to find those as well...