>From c01eb04cb031f38fe3270de5a75a3809b1034750 Mon Sep 17 00:00:00 2001 From: akater Date: Wed, 15 Sep 2021 19:42:47 +0000 Subject: [PATCH] Add cl-map-into map-into is a standard Common Lisp function that acts as cl-map, only values are recorded into a preallocated sequence. * lisp/emacs-lisp/cl-extra.el (cl-map-into): New primary function (cl--map-into-basic-call-arguments-limit, cl--map-into-max-small-signature): New auxillary constant (cl--map-into-mappers-array, cl--map-into-mappers-alist): New variable (cl--compute-map-into-signature, cl--make-map-into-mapper): New auxillary function (cl--do-seq-type-signature): New auxillary macro --- lisp/emacs-lisp/cl-extra.el | 228 ++++++++++++++++++++++++++++++++++++ 1 file changed, 228 insertions(+) diff --git a/lisp/emacs-lisp/cl-extra.el b/lisp/emacs-lisp/cl-extra.el index 3840d13ecf..84ce153758 100644 --- a/lisp/emacs-lisp/cl-extra.el +++ b/lisp/emacs-lisp/cl-extra.el @@ -88,6 +88,234 @@ defun cl-equalp (x y) (t (equal x y)))) +;;; map-into + +;; We implement a simple dispatcher for sequence types. +;; +;; cl-extra has cl--mapcar-many for similar purpose. +;; The core issue with it, it goes through args pre-emptively +;; to compute min length when there are more than 2 arguments +;; which makes it and its reverse dependencies fail on circular lists +;; unless there are <3 args. +;; Other issues are +;; - it performs type checks for sequences of known types at runtime +;; - it may cons whole arglist thrice per invocation +;; - looks like it's hard to extend. + +;; Our approach doesn't have these issues. + +(defconst cl--map-into-basic-call-arguments-limit 7 + "Maximal reasonably expected number of arguments to `cl-map-into'. + +`cl-map-into' caches its code corresponding to various signature +types of arglists supplied to `cl-map-into'. Arglists may vary +in length. + +Code corresponding to arglists of length less than +`cl--map-into-basic-call-arguments-limit' is accessed via array. + +Code corresponding to arglists of length greater than or equal to +`cl--map-into-basic-call-arguments-limit' is accessed via alist. +") + +(defconst cl--map-into-max-small-signature + (expt 2 cl--map-into-basic-call-arguments-limit) + "Length of array to allocate for caching `cl-map-into' mappers +corresponding to small arglists. + +Such mappers are accessed by their position in an array; position +equals the signature. + +Consider `cl-map-into' arglist + +(target f seq-1 seq-2) + +call-arguments-limit corresponding to arglists of this length or +shorter, is 4 (as there are 4 arguments). This leaves at most 3 +sequences to contribute to type signature. + +Hovewer, we have to store one additional bit for fixnum-based +encoding to be unambiguous and simple. So overall array length +ends up being exactly (expt 2 call-arguments-limit).") + +(defvar cl--map-into-mappers-array + (make-vector cl--map-into-max-small-signature nil) + "Array holding mappers corresponding to small arglists of `cl-map-into'. + +Element type is (or function null).") + +(defvar cl--map-into-mappers-alist nil + "Alist holding mappers corresponding to large arglists of `cl-map-into'.") + +(defun cl--compute-map-into-signature (&rest all-sequences) + "Compute lookup key for `cl-map-into''s almost-arglist ALL-SEQUENCES. + +Namely: ALL-SEQUENCES would be (TARGET &rest SEQUENCES) + for (cl-map-into TARGET f &rest SEQUENCES) + +As a side effect, it checks that ALL-SEQUENCES are of sequence +types. + +Example: +ELISP> (mapcar (lambda (arglist) + (apply #'cl--compute-map-into-signature arglist)) + '(( () () () ) ; signature #b1000 + ( () () [] ) ; signature #b1001 + ( () [] () ) ; signature #b1010 + ( () [] [] ) ; signature #b1011 + ( [] () () ) ; signature #b1100 + )) +(8 9 10 11 12)" + ;; This is not `cl-map-into'-specific and could be used for other caches + ;; which is why we don't specify arglist as (target &rest sequences). + ;; For the time being (while this dispatch is not used widely), + ;; neither docstring nor name reflect this. + (let ((signature 1)) + (dolist (s all-sequences signature) + (setq signature (ash signature 1)) + (cl-etypecase s + (list) + (vector (cl-incf signature)))))) + +;; ;; todo: move to tests + +;; (cl-map-into (list 0 0 0) #'+ [41 40 39] '(1 2 3)) +;; (cl-map-into (list 0 0 0) #'+ '(1 2 3) [41 40 39]) + +;; (let ((s (list 0 0 0))) +;; (cl-map-into s #'+ '(1 2 3) [41 40 39]) +;; s) +;; (let ((s (cl-coerce '(18 19 20) 'vector))) +;; (cl-map-into s #'+ s '(6 4 2 1 not-even-a-number) s) +;; s) + +(cl-defmacro cl--do-seq-type-signature ((type-var signature &optional result) + &body body) + "With TYPE-VAR bound to sequence type, evaluate BODY forms. Return RESULT. + +TYPE-VAR goes across sequence types in an arglist corresponding +to SIGNATURE that encodes sequence types in that arglist. + +Iteration goes from arglist's end to arglist's start. + +If :first is present at toplevel in BODY, all forms following +it (and those forms only) are evaluated in order when TYPE-VAR is +bound to the first sequence type in the arglist --- which would +be the last sequence type derived from SIGNATURE: see the +previous paragraph. At other iteration steps, only forms +preceding the first :first are evaluated. + +Subsequent instances of toplevel :first in BODY don't affect anything." + (declare (indent 1)) + (let* ((main (cl-copy-list body)) + (first (if (eq :first (car main)) (progn (setf main nil) + (cdr main)) + (cl-loop with sublist = main + while sublist do + (when (eq :first (cadr sublist)) + (setf first (cddr sublist) (cdr sublist) nil) + (cl-return first)) + (pop sublist))))) + (let ((sig (gensym "sig-"))) + `(let ((,sig ,signature) ,type-var) + ;; (declare (type (integer (1)) ,sig) + ;; ;; Let's keep nil for now. + ;; (type (member nil list vector) ,type-var)) + (cl-check-type ,sig (integer (1))) + (cl-loop (cond + ((or (when (= 2 ,sig) (setq ,type-var 'list)) + (when (= 3 ,sig) (setq ,type-var 'vector))) + ;; TODO: This duplicates main code sometimes, + ;; think of elegant enough way to eliminate duplication. + ,@(or first main) (cl-return ,result)) + (t (setq ,type-var (if (zerop (mod ,sig 2)) + 'list + 'vector)) + ,@main)) + (setf ,sig (floor ,sig 2))))))) + +(defun cl--make-map-into-mapper (signature &optional do-not-compile) + "Return mapper for `cl-map-into' specialized on arglists of type encoded by SIGNATURE. + +If DO-NOT-COMPILE is nil (default), return byte-compiled function. +Otherwise, return lambda form. + +Example: +ELISP> (cl--make-map-into-mapper #b1011 t) +(lambda (f target-list vector-2 vector-1) + (cl-symbol-macrolet ((place (car target-cons))) + (cl-loop for target-cons on target-list + for elt-2 across vector-2 + for elt-1 across vector-1 + do (setf place (funcall f elt-2 elt-1)) + finally return target-list)))" + (let ((gensym-counter 1) f xs ss loop + target-type target-index target-place target-var) + (cl-macrolet ((nconcf (var &rest seqs) `(setf ,var (nconc ,@seqs ,var)))) + ;; The only good thing about this name is, it's short and ends with f + (cl--do-seq-type-signature (type signature) + (nconcf loop (list 'for (let ((it (gensym "elt-"))) + (push it xs) + (cl-decf gensym-counter) + it) + (cl-case type + (list 'in) + (vector 'across)) + (let ((it (gensym (concat (symbol-name type) "-")))) + (push it ss) + it))) + :first (setq target-type type + target-var (make-symbol + (concat "target-" (symbol-name target-type)))) + (nconcf loop (list 'for) + (cl-case type + (list (list (setq target-index (make-symbol "target-cons")) + 'on target-var)) + (vector (list (setq target-index (gensym "target-i")) + 'to `(1- (length ,target-var)))))))) + (funcall + (if do-not-compile #'identity #'byte-compile) + `(lambda ,(cons (setq f (make-symbol "f")) (cons target-var ss)) + (cl-symbol-macrolet ((,(setq target-place (make-symbol "place")) + ,(cl-case target-type + (list `(car ,target-index)) + (vector `(aref ,target-var ,target-index))))) + (cl-loop ,@(nconc loop `(do (setf ,target-place (funcall ,f ,@xs)) + ;; Bytecode looks better + ;; with finally return .. + ;; than with finally (cl-return ..). + finally return ,target-var)))))))) + +(defun cl-map-into (target function &rest sequences) + "Common Lisp's map-into. + +Destructively modify TARGET to contain the results of applying +FUNCTION to each element in the argument SEQUENCES in turn. + +TARGET and each element of SEQUENCES can each be either a list +or a vector. If TARGET and each element of SEQUENCES are not +all the same length, the iteration terminates when the shortest sequence +(of any of the SEQUENCES or the TARGET) is exhausted. If TARGET +is longer than the shortest element of SEQUENCES, extra elements +at the end of TARGET are left unchanged." + (cl-check-type function function) + (apply + (let* ((sig (apply #'cl--compute-map-into-signature target sequences)) + (small (< sig cl--map-into-max-small-signature))) + (cl-symbol-macrolet ((basic-cache (aref cl--map-into-mappers-array sig)) + (general-cache + ;; TODO: Order alist entries for faster lookup + ;; (note that we'll have to abandon alist-get then). + (alist-get sig cl--map-into-mappers-alist + nil nil #'=))) + (or (and small basic-cache) + (and (not small) general-cache) + (let ((mapper (cl--make-map-into-mapper sig))) + (if small (setf basic-cache mapper) + (setf general-cache mapper)))))) + function target sequences)) + + ;;; Control structures. ;;;###autoload -- 2.32.0