cl-generic.el 34.4 KB
Newer Older
1 2
;;; cl-generic.el --- CLOS-style generic functions for Elisp  -*- lexical-binding: t; -*-

3
;; Copyright (C) 2015 Free Software Foundation, Inc.
4 5 6

;; Author: Stefan Monnier <monnier@iro.umontreal.ca>

7 8 9
;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
10 11 12 13
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

14
;; GNU Emacs is distributed in the hope that it will be useful,
15 16 17 18 19
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
20
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
21 22 23 24 25 26 27 28

;;; Commentary:

;; This implements the most of CLOS's multiple-dispatch generic functions.
;; To use it you need either (require 'cl-generic) or (require 'cl-lib).
;; The main entry points are: `cl-defgeneric' and `cl-defmethod'.

;; Missing elements:
29
;; - We don't support make-method, call-method, define-method-combination.
30 31 32 33 34 35 36 37 38 39
;; - Method and generic function objects: CLOS defines methods as objects
;;   (same for generic functions), whereas we don't offer such an abstraction.
;; - `no-next-method' should receive the "calling method" object, but since we
;;   don't have such a thing, we pass nil instead.
;; - In defgeneric we don't support the options:
;;   declare, :method-combination, :generic-function-class, :method-class,
;;   :method.
;; Added elements:
;; - We support aliases to generic functions.
;; - The kind of thing on which to dispatch can be extended.
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
;;   There is support in this file for dispatch on:
;;   - (eql <val>)
;;   - plain old types
;;   - type of CL structs
;;   eieio-core adds dispatch on:
;;   - class of eieio objects
;;   - actual class argument, using the syntax (subclass <class>).

;; Efficiency considerations: overall, I've made an effort to make this fairly
;; efficient for the expected case (e.g. no constant redefinition of methods).
;; - Generic functions which do not dispatch on any argument are implemented
;;   optimally (just as efficient as plain old functions).
;; - Generic functions which only dispatch on one argument are fairly efficient
;;   (not a lot of room for improvement, I think).
;; - Multiple dispatch is implemented rather naively.  There's an extra `apply'
;;   function call for every dispatch; we don't optimize each dispatch
;;   based on the set of candidate methods remaining; we don't optimize the
;;   order in which we performs the dispatches either;  If/when this
;;   becomes a problem, we can try and optimize it.
;; - call-next-method could be made more efficient, but isn't too terrible.
60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100

;;; Code:

;; Note: For generic functions that dispatch on several arguments (i.e. those
;; which use the multiple-dispatch feature), we always use the same "tagcodes"
;; and the same set of arguments on which to dispatch.  This works, but is
;; often suboptimal since after one dispatch, the remaining dispatches can
;; usually be simplified, or even completely skipped.

(eval-when-compile (require 'cl-lib))
(eval-when-compile (require 'pcase))

(defvar cl-generic-tagcode-function
  (lambda (type _name)
    (if (eq type t) '(0 . 'cl--generic-type)
      (error "Unknown specializer %S" type)))
  "Function to get the Elisp code to extract the tag on which we dispatch.
Takes a \"parameter-specializer-name\" and a variable name, and returns
a pair (PRIORITY . CODE) where CODE is an Elisp expression that should be
used to extract the \"tag\" (from the object held in the named variable)
that should uniquely determine if we have a match
\(i.e. the \"tag\" is the value that will be used to dispatch to the proper
method(s)).
Such \"tagcodes\" will be or'd together.
PRIORITY is an integer from 0 to 100 which is used to sort the tagcodes
in the `or'.  The higher the priority, the more specific the tag should be.
More specifically, if PRIORITY is N and we have two objects X and Y
whose tag (according to TAGCODE) is `eql', then it should be the case
that for all other (PRIORITY . TAGCODE) where PRIORITY ≤ N, then
\(eval TAGCODE) for X is `eql' to (eval TAGCODE) for Y.")

(defvar cl-generic-tag-types-function
  (lambda (tag) (if (eq tag 'cl--generic-type) '(t)))
  "Function to get the list of types that a given \"tag\" matches.
They should be sorted from most specific to least specific.")

(cl-defstruct (cl--generic
               (:constructor nil)
               (:constructor cl--generic-make
                (name &optional dispatches method-table))
               (:predicate nil))
101
  (name nil :type symbol :read-only t)  ;Pointer back to the symbol.
102 103 104 105 106 107
  ;; `dispatches' holds a list of (ARGNUM . TAGCODES) where ARGNUM is the index
  ;; of the corresponding argument and TAGCODES is a list of (PRIORITY . EXP)
  ;; where the EXPs are expressions (to be `or'd together) to compute the tag
  ;; on which to dispatch and PRIORITY is the priority of each expression to
  ;; decide in which order to sort them.
  ;; The most important dispatch is last in the list (and the least is first).
108
  (dispatches nil :type (list-of (cons natnum (list-of tagcode))))
109 110 111 112
  ;; `method-table' is a list of
  ;; ((SPECIALIZERS . QUALIFIER) USES-CNM . FUNCTION), where
  ;; USES-CNM is a boolean indicating if FUNCTION calls `cl-call-next-method'
  ;; (and hence expects an extra argument holding the next-method).
113 114
  (method-table nil :type (list-of (cons (cons (list-of type) keyword)
                                         (cons boolean function)))))
115 116 117 118 119 120 121 122 123 124 125 126

(defmacro cl--generic (name)
  `(get ,name 'cl--generic))

(defun cl-generic-ensure-function (name)
  (let (generic
        (origname name))
    (while (and (null (setq generic (cl--generic name)))
                (fboundp name)
                (symbolp (symbol-function name)))
      (setq name (symbol-function name)))
    (unless (or (not (fboundp name))
127
                (autoloadp (symbol-function name))
128 129 130 131 132 133 134 135 136 137
                (and (functionp name) generic))
      (error "%s is already defined as something else than a generic function"
             origname))
    (if generic
        (cl-assert (eq name (cl--generic-name generic)))
      (setf (cl--generic name) (setq generic (cl--generic-make name)))
      (defalias name (cl--generic-make-function generic)))
    generic))

(defun cl--generic-setf-rewrite (name)
138 139 140 141 142 143 144 145 146 147
  (let* ((setter (intern (format "cl-generic-setter--%s" name)))
         (exp `(unless (eq ',setter (get ',name 'cl-generic-setter))
                 ;; (when (get ',name 'gv-expander)
                 ;;   (error "gv-expander conflicts with (setf %S)" ',name))
                 (setf (get ',name 'cl-generic-setter) ',setter)
                 (gv-define-setter ,name (val &rest args)
                   (cons ',setter (cons val args))))))
    ;; Make sure `setf' can be used right away, e.g. in the body of the method.
    (eval exp t)
    (cons setter exp)))
148 149 150 151 152 153

;;;###autoload
(defmacro cl-defgeneric (name args &rest options-and-methods)
  "Create a generic function NAME.
DOC-STRING is the base documentation for this class.  A generic
function has no body, as its purpose is to decide which method body
154
is appropriate to use.  Specific methods are defined with `cl-defmethod'.
155
With this implementation the ARGS are currently ignored.
156 157 158
OPTIONS-AND-METHODS currently understands:
- (:documentation DOCSTRING)
- (declare DECLARATIONS)"
159 160 161 162 163 164 165 166
  (declare (indent 2) (doc-string 3))
  (let* ((docprop (assq :documentation options-and-methods))
         (doc (cond ((stringp (car-safe options-and-methods))
                     (pop options-and-methods))
                    (docprop
                     (prog1
                         (cadr docprop)
                       (setq options-and-methods
167 168 169 170 171
                             (delq docprop options-and-methods))))))
         (declarations (assq 'declare options-and-methods)))
    (when declarations
      (setq options-and-methods
            (delq declarations options-and-methods)))
172 173 174 175 176 177
    `(progn
       ,(when (eq 'setf (car-safe name))
          (pcase-let ((`(,setter . ,code) (cl--generic-setf-rewrite
                                           (cadr name))))
            (setq name setter)
            code))
178 179 180 181 182 183 184 185 186
       ,@(mapcar (lambda (declaration)
                   (let ((f (cdr (assq (car declaration)
                                       defun-declarations-alist))))
                     (cond
                      (f (apply (car f) name args (cdr declaration)))
                      (t (message "Warning: Unknown defun property `%S' in %S"
                                  (car declaration) name)
                         nil))))
                 (cdr declarations))
187 188
       (defalias ',name
         (cl-generic-define ',name ',args ',options-and-methods)
189
         ,(help-add-fundoc-usage doc args)))))
190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211

(defun cl--generic-mandatory-args (args)
  (let ((res ()))
    (while (not (memq (car args) '(nil &rest &optional &key)))
      (push (pop args) res))
    (nreverse res)))

;;;###autoload
(defun cl-generic-define (name args options-and-methods)
  (let ((generic (cl-generic-ensure-function name))
        (mandatory (cl--generic-mandatory-args args))
        (apo (assq :argument-precedence-order options-and-methods)))
    (setf (cl--generic-dispatches generic) nil)
    (when apo
      (dolist (arg (cdr apo))
        (let ((pos (memq arg mandatory)))
          (unless pos (error "%S is not a mandatory argument" arg))
          (push (list (- (length mandatory) (length pos)))
                (cl--generic-dispatches generic)))))
    (setf (cl--generic-method-table generic) nil)
    (cl--generic-make-function generic)))

212 213 214 215
(defmacro cl-generic-current-method-specializers ()
  "List of (VAR . TYPE) where TYPE is var's specializer.
This macro can only be used within the lexical scope of a cl-generic method."
  (error "cl-generic-current-method-specializers used outside of a method"))
216 217 218 219 220 221 222 223 224 225 226 227 228 229

(eval-and-compile         ;Needed while compiling the cl-defmethod calls below!
  (defun cl--generic-fgrep (vars sexp)    ;Copied from pcase.el.
    "Check which of the symbols VARS appear in SEXP."
    (let ((res '()))
      (while (consp sexp)
        (dolist (var (cl--generic-fgrep vars (pop sexp)))
          (unless (memq var res) (push var res))))
      (and (memq sexp vars) (not (memq sexp res)) (push sexp res))
      res))

  (defun cl--generic-lambda (args body with-cnm)
    "Make the lambda expression for a method with ARGS and BODY."
    (let ((plain-args ())
230
          (specializers nil)
231 232
          (doc-string (if (and (stringp (car-safe body)) (cdr body))
                          (pop body)))
233 234 235 236 237
          (mandatory t))
      (dolist (arg args)
        (push (pcase arg
                ((or '&optional '&rest '&key) (setq mandatory nil) arg)
                ((and `(,name . ,type) (guard mandatory))
238
                 (push (cons name (car type)) specializers)
239 240 241 242 243 244
                 name)
                (_ arg))
              plain-args))
      (setq plain-args (nreverse plain-args))
      (let ((fun `(cl-function (lambda ,plain-args
                                 ,@(if doc-string (list doc-string))
245 246 247 248
                                 ,@body)))
            (macroenv (cons `(cl-generic-current-method-specializers
                              . ,(lambda () specializers))
                            macroexpand-all-environment)))
249
        (require 'cl-lib)        ;Needed to expand `cl-flet' and `cl-function'.
250
        (if (not with-cnm)
251
            (cons nil (macroexpand-all fun macroenv))
252 253
          ;; First macroexpand away the cl-function stuff (e.g. &key and
          ;; destructuring args, `declare' and whatnot).
254
          (pcase (macroexpand fun macroenv)
255
            (`#'(lambda ,args . ,body)
256
             (let* ((doc-string (and doc-string (stringp (car body)) (cdr body)
257 258
                                     (pop body)))
                    (cnm (make-symbol "cl--cnm"))
259
                    (nmp (make-symbol "cl--nmp"))
260
                    (nbody (macroexpand-all
261 262
                            `(cl-flet ((cl-call-next-method ,cnm)
                                       (cl-next-method-p ,nmp))
263
                               ,@body)
264
                            macroenv))
265 266 267 268 269
                    ;; FIXME: Rather than `grep' after the fact, the
                    ;; macroexpansion should directly set some flag when cnm
                    ;; is used.
                    ;; FIXME: Also, optimize the case where call-next-method is
                    ;; only called with explicit arguments.
270
                    (uses-cnm (cl--generic-fgrep (list cnm nmp) nbody)))
271 272 273
               (cons (not (not uses-cnm))
                     `#'(lambda (,@(if uses-cnm (list cnm)) ,@args)
                          ,@(if doc-string (list doc-string))
274 275 276 277 278
                          ,(if (not (memq nmp uses-cnm))
                               nbody
                             `(let ((,nmp (lambda ()
                                            (cl--generic-isnot-nnm-p ,cnm))))
                                ,nbody))))))
279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302
            (f (error "Unexpected macroexpansion result: %S" f))))))))


;;;###autoload
(defmacro cl-defmethod (name args &rest body)
  "Define a new method for generic function NAME.
I.e. it defines the implementation of NAME to use for invocations where the
value of the dispatch argument matches the specified TYPE.
The dispatch argument has to be one of the mandatory arguments, and
all methods of NAME have to use the same argument for dispatch.
The dispatch argument and TYPE are specified in ARGS where the corresponding
formal argument appears as (VAR TYPE) rather than just VAR.

The optional second argument QUALIFIER is a specifier that
modifies how the method is combined with other methods, including:
   :before  - Method will be called before the primary
   :after   - Method will be called after the primary
   :around  - Method will be called around everything else
The absence of QUALIFIER means this is a \"primary\" method.

Other than a type, TYPE can also be of the form `(eql VAL)' in
which case this method will be invoked when the argument is `eql' to VAL.

\(fn NAME [QUALIFIER] ARGS &rest [DOCSTRING] BODY)"
303 304 305 306 307 308 309 310 311
  (declare (doc-string 3) (indent 2)
           (debug
            (&define                    ; this means we are defining something
             [&or name ("setf" :name setf name)]
             ;; ^^ This is the methods symbol
             [ &optional keywordp ]     ; this is key :before etc
             list                       ; arguments
             [ &optional stringp ]      ; documentation string
             def-body)))                ; part to be debugged
312 313 314 315
  (let ((qualifiers nil)
        (setfizer (if (eq 'setf (car-safe name))
                      ;; Call it before we call cl--generic-lambda.
                      (cl--generic-setf-rewrite (cadr name)))))
316 317 318 319 320 321
    (while (keywordp args)
      (push args qualifiers)
      (setq args (pop body)))
    (pcase-let* ((with-cnm (not (memq (car qualifiers) '(:before :after))))
                 (`(,uses-cnm . ,fun) (cl--generic-lambda args body with-cnm)))
      `(progn
322 323 324
         ,(when setfizer
            (setq name (car setfizer))
            (cdr setfizer))
325 326 327 328 329 330 331
         ,(and (get name 'byte-obsolete-info)
               (or (not (fboundp 'byte-compile-warning-enabled-p))
                   (byte-compile-warning-enabled-p 'obsolete))
               (let* ((obsolete (get name 'byte-obsolete-info)))
                 (macroexp--warn-and-return
                  (macroexp--obsolete-warning name obsolete "generic function")
                  nil)))
332 333 334 335 336
         ;; You could argue that `defmethod' modifies rather than defines the
         ;; function, so warnings like "not known to be defined" are fair game.
         ;; But in practice, it's common to use `cl-defmethod'
         ;; without a previous `cl-defgeneric'.
         (declare-function ,name "")
337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357
         (cl-generic-define-method ',name ',qualifiers ',args
                                   ,uses-cnm ,fun)))))

;;;###autoload
(defun cl-generic-define-method (name qualifiers args uses-cnm function)
  (when (> (length qualifiers) 1)
    (error "We only support a single qualifier per method: %S" qualifiers))
  (unless (memq (car qualifiers) '(nil :primary :around :after :before))
    (error "Unsupported qualifier in: %S" qualifiers))
  (let* ((generic (cl-generic-ensure-function name))
         (mandatory (cl--generic-mandatory-args args))
         (specializers
          (mapcar (lambda (arg) (if (consp arg) (cadr arg) t)) mandatory))
         (key (cons specializers (or (car qualifiers) ':primary)))
         (mt (cl--generic-method-table generic))
         (me (assoc key mt))
         (dispatches (cl--generic-dispatches generic))
         (i 0))
    (dolist (specializer specializers)
      (let* ((tagcode (funcall cl-generic-tagcode-function specializer 'arg))
             (x (assq i dispatches)))
358 359 360 361 362 363 364 365
        (unless x
          (setq x (list i (funcall cl-generic-tagcode-function t 'arg)))
          (setf (cl--generic-dispatches generic)
                (setq dispatches (cons x dispatches))))
        (unless (member tagcode (cdr x))
          (setf (cdr x)
                (nreverse (sort (cons tagcode (cdr x))
                                #'car-less-than-car))))
366 367 368
        (setq i (1+ i))))
    (if me (setcdr me (cons uses-cnm function))
      (setf (cl--generic-method-table generic)
369
            (cons `(,key ,uses-cnm . ,function) mt)))
370 371
    (cl-pushnew `(cl-defmethod . (,(cl--generic-name generic) . ,specializers))
                current-load-list :test #'equal)
372 373 374 375
    (let ((gfun (cl--generic-make-function generic))
          ;; Prevent `defalias' from recording this as the definition site of
          ;; the generic function.
          current-load-list)
376 377
      ;; For aliases, cl--generic-name gives us the actual name.
      (defalias (cl--generic-name generic) gfun))))
378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393

(defmacro cl--generic-with-memoization (place &rest code)
  (declare (indent 1) (debug t))
  (gv-letplace (getter setter) place
    `(or ,getter
         ,(macroexp-let2 nil val (macroexp-progn code)
            `(progn
               ,(funcall setter val)
               ,val)))))

(defvar cl--generic-dispatchers (make-hash-table :test #'equal))

(defun cl--generic-get-dispatcher (tagcodes dispatch-arg)
  (cl--generic-with-memoization
      (gethash (cons dispatch-arg tagcodes) cl--generic-dispatchers)
    (let ((lexical-binding t)
394 395 396 397 398 399 400 401
          (tag-exp `(or ,@(mapcar #'cdr
				  ;; Minor optimization: since this tag-exp is
				  ;; only used to lookup the method-cache, it
				  ;; doesn't matter if the default value is some
				  ;; constant or nil.
				  (if (macroexp-const-p (car (last tagcodes)))
				      (butlast tagcodes)
				    tagcodes))))
402 403 404 405 406 407 408 409
          (extraargs ()))
      (dotimes (_ dispatch-arg)
        (push (make-symbol "arg") extraargs))
      (byte-compile
       `(lambda (generic dispatches-left)
          (let ((method-cache (make-hash-table :test #'eql)))
            (lambda (,@extraargs arg &rest args)
              (apply (cl--generic-with-memoization
410
                         (gethash ,tag-exp method-cache)
411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465
                       (cl--generic-cache-miss
                        generic ',dispatch-arg dispatches-left
                        (list ,@(mapcar #'cdr tagcodes))))
                     ,@extraargs arg args))))))))

(defun cl--generic-make-function (generic)
  (let* ((dispatches (cl--generic-dispatches generic))
         (dispatch
          (progn
            (while (and dispatches
                        (member (cdar dispatches)
                                '(nil ((0 . 'cl--generic-type)))))
              (setq dispatches (cdr dispatches)))
            (pop dispatches))))
    (if (null dispatch)
        (cl--generic-build-combined-method
         (cl--generic-name generic)
	 (cl--generic-method-table generic))
      (let ((dispatcher (cl--generic-get-dispatcher
                         (cdr dispatch) (car dispatch))))
        (funcall dispatcher generic dispatches)))))

(defun cl--generic-nest (fun methods)
  (pcase-dolist (`(,uses-cnm . ,method) methods)
    (setq fun
          (if (not uses-cnm) method
            (let ((next fun))
              (lambda (&rest args)
                (apply method
                       ;; FIXME: This sucks: passing just `next' would
                       ;; be a lot more efficient than the lambda+apply
                       ;; quasi-η, but we need this to implement the
                       ;; "if call-next-method is called with no
                       ;; arguments, then use the previous arguments".
                       (lambda (&rest cnm-args)
                         (apply next (or cnm-args args)))
                       args))))))
  fun)

(defvar cl--generic-combined-method-memoization
  (make-hash-table :test #'equal :weakness 'value)
  "Table storing previously built combined-methods.
This is particularly useful when many different tags select the same set
of methods, since this table then allows us to share a single combined-method
for all those different tags in the method-cache.")

(defun cl--generic-build-combined-method (generic-name methods)
  (let ((mets-by-qual ()))
    (dolist (qm methods)
      (push (cdr qm) (alist-get (cdar qm) mets-by-qual)))
    (cl--generic-with-memoization
        (gethash (cons generic-name mets-by-qual)
                 cl--generic-combined-method-memoization)
      (cond
       ((null mets-by-qual) (lambda (&rest args)
466 467
                              (apply #'cl-no-applicable-method
                                     generic-name args)))
468 469 470 471 472 473
       (t
        (let* ((fun (lambda (&rest args)
                      ;; FIXME: CLOS passes as second arg the "calling method".
                      ;; We don't currently have "method objects" like CLOS
                      ;; does so we can't really do it the CLOS way.
                      ;; The closest would be to pass the lambda corresponding
474 475 476 477 478 479
                      ;; to the method, or maybe the ((SPECIALIZERS
                      ;; . QUALIFIER) USE-CNM . FUNCTION) entry from the method
                      ;; table, but the caller wouldn't be able to do much with
                      ;; it anyway.  So we pass nil for now.
                      ;; FIXME: signal `no-primary-method' if there's
                      ;; no primary.
480 481 482 483 484 485 486 487 488 489 490
                      (apply #'cl-no-next-method generic-name nil args)))
               ;; We use `cdr' to drop the `uses-cnm' annotations.
               (before
                (mapcar #'cdr (reverse (alist-get :before mets-by-qual))))
               (after (mapcar #'cdr (alist-get :after mets-by-qual))))
          (setq fun (cl--generic-nest fun (alist-get :primary mets-by-qual)))
          (when (or after before)
            (let ((next fun))
              (setq fun (lambda (&rest args)
                          (dolist (bf before)
                            (apply bf args))
491 492 493 494
                          (prog1
                              (apply next args)
                            (dolist (af after)
                              (apply af args)))))))
495 496
          (cl--generic-nest fun (alist-get :around mets-by-qual))))))))

497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528
(defconst cl--generic-nnm-sample
  (cl--generic-build-combined-method nil '(((specializer . :qualifier)))))
(defconst cl--generic-cnm-sample
  (funcall (cl--generic-build-combined-method
            nil `(((specializer . :primary) t . ,#'identity)))))

(defun cl--generic-isnot-nnm-p (cnm)
  "Return non-nil if CNM is the function that calls `cl-no-next-method'."
  ;; ¡Big Gross Ugly Hack!
  ;; `next-method-p' just sucks, we should let it die.  But EIEIO did support
  ;; it, and some packages use it, so we need to support it.
  (catch 'found
    (cl-assert (function-equal cnm cl--generic-cnm-sample))
    (if (byte-code-function-p cnm)
        (let ((cnm-constants (aref cnm 2))
              (sample-constants (aref cl--generic-cnm-sample 2)))
          (dotimes (i (length sample-constants))
            (when (function-equal (aref sample-constants i)
                                  cl--generic-nnm-sample)
              (throw 'found
                     (not (function-equal (aref cnm-constants i)
                                          cl--generic-nnm-sample))))))
      (cl-assert (eq 'closure (car-safe cl--generic-cnm-sample)))
      (let ((cnm-env (cadr cnm)))
        (dolist (vb (cadr cl--generic-cnm-sample))
          (when (function-equal (cdr vb) cl--generic-nnm-sample)
            (throw 'found
                   (not (function-equal (cdar cnm-env)
                                        cl--generic-nnm-sample))))
          (setq cnm-env (cdr cnm-env)))))
    (error "Haven't found no-next-method-sample in cnm-sample")))

529 530 531 532
(defun cl--generic-cache-miss (generic dispatch-arg dispatches-left tags)
  (let ((types (apply #'append (mapcar cl-generic-tag-types-function tags)))
        (methods '()))
    (dolist (method-desc (cl--generic-method-table generic))
533 534
      (let* ((specializer (or (nth dispatch-arg (caar method-desc)) t))
             (m (member specializer types)))
535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553
        (when m
          (push (cons (length m) method-desc) methods))))
    ;; Sort the methods, most specific first.
    ;; It would be tempting to sort them once and for all in the method-table
    ;; rather than here, but the order might depend on the actual argument
    ;; (e.g. for multiple inheritance with defclass).
    (setq methods (nreverse (mapcar #'cdr (sort methods #'car-less-than-car))))
    (cl--generic-make-function (cl--generic-make (cl--generic-name generic)
                                                 dispatches-left methods))))

;;; Define some pre-defined generic functions, used internally.

(define-error 'cl-no-method "No method for %S")
(define-error 'cl-no-next-method "No next method for %S" 'cl-no-method)
(define-error 'cl-no-applicable-method "No applicable method for %S"
  'cl-no-method)

(cl-defgeneric cl-no-next-method (generic method &rest args)
  "Function called when `cl-call-next-method' finds no next method.")
554
(cl-defmethod cl-no-next-method (generic method &rest args)
555 556 557 558
  (signal 'cl-no-next-method `(,generic ,method ,@args)))

(cl-defgeneric cl-no-applicable-method (generic &rest args)
  "Function called when a method call finds no applicable method.")
559
(cl-defmethod cl-no-applicable-method (generic &rest args)
560 561 562 563 564 565 566
  (signal 'cl-no-applicable-method `(,generic ,@args)))

(defun cl-call-next-method (&rest _args)
  "Function to call the next applicable method.
Can only be used from within the lexical body of a primary or around method."
  (error "cl-call-next-method only allowed inside primary and around methods"))

567 568 569 570 571 572
(defun cl-next-method-p ()
  "Return non-nil if there is a next method.
Can only be used from within the lexical body of a primary or around method."
  (declare (obsolete "make sure there's always a next method, or catch `cl-no-next-method' instead" "25.1"))
  (error "cl-next-method-p only allowed inside primary and around methods"))

573 574
;;; Add support for describe-function

575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595
(defun cl--generic-search-method (met-name)
  (let ((base-re (concat "(\\(?:cl-\\)?defmethod[ \t]+"
                         (regexp-quote (format "%s\\_>" (car met-name))))))
    (or
     (re-search-forward
      (concat base-re "[^&\"\n]*"
              (mapconcat (lambda (specializer)
                           (regexp-quote
                            (format "%S" (if (consp specializer)
                                             (nth 1 specializer) specializer))))
                         (remq t (cdr met-name))
                         "[ \t\n]*)[^&\"\n]*"))
      nil t)
     (re-search-forward base-re nil t))))


(with-eval-after-load 'find-func
  (defvar find-function-regexp-alist)
  (add-to-list 'find-function-regexp-alist
               `(cl-defmethod . ,#'cl--generic-search-method)))

596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613
(defun cl--generic-method-info (method)
  (pcase-let ((`((,specializers . ,qualifier) ,uses-cnm . ,function) method))
    (let* ((args (help-function-arglist function 'names))
           (docstring (documentation function))
           (doconly (if docstring
                        (let ((split (help-split-fundoc docstring nil)))
                          (if split (cdr split) docstring))))
           (combined-args ()))
      (if uses-cnm (setq args (cdr args)))
      (dolist (specializer specializers)
        (let ((arg (if (eq '&rest (car args))
                       (intern (format "arg%d" (length combined-args)))
                     (pop args))))
          (push (if (eq specializer t) arg (list arg specializer))
                combined-args)))
      (setq combined-args (append (nreverse combined-args) args))
      (list qualifier combined-args doconly))))

614
(add-hook 'help-fns-describe-function-functions #'cl--generic-describe)
615 616 617
(defun cl--generic-describe (function)
  (let ((generic (if (symbolp function) (cl--generic function))))
    (when generic
618
      (require 'help-mode)              ;Needed for `help-function-def' button!
619 620 621 622
      (save-excursion
        (insert "\n\nThis is a generic function.\n\n")
        (insert (propertize "Implementations:\n\n" 'face 'bold))
        ;; Loop over fanciful generics
623 624
        (dolist (method (cl--generic-method-table generic))
          (let* ((info (cl--generic-method-info method)))
625
            ;; FIXME: Add hyperlinks for the types as well.
626 627
            (insert (format "%S %S" (nth 0 info) (nth 1 info)))
            (let* ((met-name (cons function (caar method)))
628 629 630 631 632 633 634
                   (file (find-lisp-object-file-name met-name 'cl-defmethod)))
              (when file
                (insert " in `")
                (help-insert-xref-button (help-fns-short-filename file)
                                         'help-function-def met-name file
                                         'cl-defmethod)
                (insert "'.\n")))
635
            (insert "\n" (or (nth 2 info) "Undocumented") "\n\n")))))))
636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760

;;; Support for (eql <val>) specializers.

(defvar cl--generic-eql-used (make-hash-table :test #'eql))

(add-function :before-until cl-generic-tagcode-function
              #'cl--generic-eql-tagcode)
(defun cl--generic-eql-tagcode (type name)
  (when (eq (car-safe type) 'eql)
    (puthash (cadr type) type cl--generic-eql-used)
    `(100 . (gethash ,name cl--generic-eql-used))))

(add-function :before-until cl-generic-tag-types-function
              #'cl--generic-eql-tag-types)
(defun cl--generic-eql-tag-types (tag)
  (if (eq (car-safe tag) 'eql) (list tag)))

;;; Support for cl-defstructs specializers.

(add-function :before-until cl-generic-tagcode-function
              #'cl--generic-struct-tagcode)
(defun cl--generic-struct-tagcode (type name)
  (and (symbolp type)
       (get type 'cl-struct-type)
       (or (eq 'vector (car (get type 'cl-struct-type)))
           (error "Can't dispatch on cl-struct %S: type is %S"
                  type (car (get type 'cl-struct-type))))
       (or (equal '(cl-tag-slot) (car (get type 'cl-struct-slots)))
           (error "Can't dispatch on cl-struct %S: no tag in slot 0"
                  type))
       ;; We could/should check the vector has length >0,
       ;; but really, mixing vectors and structs is a bad idea,
       ;; so let's not waste time trying to handle the case
       ;; of an empty vector.
       ;; BEWARE: this returns a bogus tag for non-struct vectors.
       `(50 . (and (vectorp ,name) (aref ,name 0)))))

(add-function :before-until cl-generic-tag-types-function
              #'cl--generic-struct-tag-types)
(defun cl--generic-struct-tag-types (tag)
  ;; FIXME: cl-defstruct doesn't make it easy for us.
  (and (symbolp tag)
       ;; A method call shouldn't itself mess with the match-data.
       (string-match-p "\\`cl-struct-\\(.*\\)" (symbol-name tag))
       (let ((types (list (intern (substring (symbol-name tag) 10)))))
         (while (get (car types) 'cl-struct-include)
           (push (get (car types) 'cl-struct-include) types))
         (push 'cl-struct types)        ;The "parent type" of all cl-structs.
         (nreverse types))))

;;; Dispatch on "old-style types".

(defconst cl--generic-typeof-types
  ;; Hand made from the source code of `type-of'.
  '((integer number) (symbol) (string array) (cons list)
    ;; Markers aren't `numberp', yet they are accepted wherever integers are
    ;; accepted, pretty much.
    (marker) (overlay) (float number) (window-configuration)
    (process) (window) (subr) (compiled-function) (buffer) (char-table array)
    (bool-vector array)
    (frame) (hash-table) (font-spec) (font-entity) (font-object)
    (vector array)
    ;; Plus, hand made:
    (null list symbol)
    (list)
    (array)
    (number)))

(add-function :before-until cl-generic-tagcode-function
              #'cl--generic-typeof-tagcode)
(defun cl--generic-typeof-tagcode (type name)
  ;; FIXME: Add support for other types accepted by `cl-typep' such
  ;; as `character', `atom', `face', `function', ...
  (and (assq type cl--generic-typeof-types)
       (progn
         (if (memq type '(vector array))
             (message "`%S' also matches CL structs and EIEIO classes" type))
         ;; FIXME: We could also change `type-of' to return `null' for nil.
         `(10 . (if ,name (type-of ,name) 'null)))))

(add-function :before-until cl-generic-tag-types-function
              #'cl--generic-typeof-types)
(defun cl--generic-typeof-types (tag)
  (and (symbolp tag)
       (assq tag cl--generic-typeof-types)))

;;; Just for kicks: dispatch on major-mode
;;
;; Here's how you'd use it:
;;   (cl-defmethod foo ((x (major-mode text-mode)) y z) ...)
;; And then
;;     (foo 'major-mode toto titi)
;;
;; FIXME: Better would be to do that via dispatch on an "implicit argument".

;; (defvar cl--generic-major-modes (make-hash-table :test #'eq))
;;
;; (add-function :before-until cl-generic-tagcode-function
;;               #'cl--generic-major-mode-tagcode)
;; (defun cl--generic-major-mode-tagcode (type name)
;;   (if (eq 'major-mode (car-safe type))
;;       `(50 . (if (eq ,name 'major-mode)
;;                  (cl--generic-with-memoization
;;                      (gethash major-mode cl--generic-major-modes)
;;                    `(cl--generic-major-mode . ,major-mode))))))
;;
;; (add-function :before-until cl-generic-tag-types-function
;;               #'cl--generic-major-mode-types)
;; (defun cl--generic-major-mode-types (tag)
;;   (when (eq (car-safe tag) 'cl--generic-major-mode)
;;     (if (eq tag 'fundamental-mode) '(fundamental-mode t)
;;       (let ((types `((major-mode ,(cdr tag)))))
;;         (while (get (car types) 'derived-mode-parent)
;;           (push (list 'major-mode (get (car types) 'derived-mode-parent))
;;                 types))
;;         (unless (eq 'fundamental-mode (car types))
;;           (push '(major-mode fundamental-mode) types))
;;         (nreverse types)))))

;; Local variables:
;; generated-autoload-file: "cl-loaddefs.el"
;; End:

(provide 'cl-generic)
;;; cl-generic.el ends here