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+;;; seq-25.el --- seq.el implementation for Emacs 25.x -*- lexical-binding: t -*-
+
+;; Copyright (C) 2014-2016 Free Software Foundation, Inc.
+
+;; Author: Nicolas Petton <nicolas@petton.fr>
+;; Keywords: sequences
+
+;; Maintainer: emacs-devel@gnu.org
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; 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.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; 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
+;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Sequence-manipulation functions that complement basic functions
+;; provided by subr.el.
+;;
+;; All functions are prefixed with "seq-".
+;;
+;; All provided functions work on lists, strings and vectors.
+;;
+;; Functions taking a predicate or iterating over a sequence using a
+;; function as argument take the function as their first argument and
+;; the sequence as their second argument.  All other functions take
+;; the sequence as their first argument.
+;;
+;; seq.el can be extended to support new type of sequences.  Here are
+;; the generic functions that must be implemented by new seq types:
+;; - `seq-elt'
+;; - `seq-length'
+;; - `seq-do'
+;; - `seqp'
+;; - `seq-subseq'
+;; - `seq-into-sequence'
+;; - `seq-copy'
+;; - `seq-into'
+
+;;; Code:
+
+;; When loading seq.el in Emacs 24.x, this file gets byte-compiled, even if
+;; never used.  This takes care of byte-compilation warnings is emitted, by
+;; emitting nil in the macro expansion in Emacs 24.x.
+(defmacro seq--when-emacs-25-p (&rest body)
+  "Execute BODY if in Emacs>=25.x."
+  (declare (indent (lambda (&rest x) 0)) (debug t))
+  (when (version<= "25" emacs-version)
+    `(progn ,@body)))
+
+(seq--when-emacs-25-p
+
+(require 'cl-generic)
+(require 'cl-lib) ;; for cl-subseq
+
+(defmacro seq-doseq (spec &rest body)
+  "Loop over a sequence.
+Evaluate BODY with VAR bound to each element of SEQUENCE, in turn.
+
+Similar to `dolist' but can be applied to lists, strings, and vectors.
+
+\(fn (VAR SEQUENCE) BODY...)"
+  (declare (indent 1) (debug ((symbolp form &optional form) body)))
+  `(seq-do (lambda (,(car spec))
+             ,@body)
+           ,(cadr spec)))
+
+(pcase-defmacro seq (&rest patterns)
+  "Build a `pcase' pattern that matches elements of SEQUENCE.
+
+The `pcase' pattern will match each element of PATTERNS against the
+corresponding element of SEQUENCE.
+
+Extra elements of the sequence are ignored if fewer PATTERNS are
+given, and the match does not fail."
+  `(and (pred seqp)
+        ,@(seq--make-pcase-bindings patterns)))
+
+(defmacro seq-let (args sequence &rest body)
+  "Bind the variables in ARGS to the elements of SEQUENCE, then evaluate BODY.
+
+ARGS can also include the `&rest' marker followed by a variable
+name to be bound to the rest of SEQUENCE."
+  (declare (indent 2) (debug t))
+  `(pcase-let ((,(seq--make-pcase-patterns args) ,sequence))
+     ,@body))
+
+
+;;; Basic seq functions that have to be implemented by new sequence types
+(cl-defgeneric seq-elt (sequence n)
+  "Return Nth element of SEQUENCE."
+  (elt sequence n))
+
+;; Default gv setters for `seq-elt'.
+;; It can be a good idea for new sequence implementations to provide a
+;; "gv-setter" for `seq-elt'.
+(cl-defmethod (setf seq-elt) (store (sequence array) n)
+  (aset sequence n store))
+
+(cl-defmethod (setf seq-elt) (store (sequence cons) n)
+  (setcar (nthcdr n sequence) store))
+
+(cl-defgeneric seq-length (sequence)
+  "Return the number of elements of SEQUENCE."
+  (length sequence))
+
+(cl-defgeneric seq-do (function sequence)
+  "Apply FUNCTION to each element of SEQUENCE, presumably for side effects.
+Return SEQUENCE."
+  (mapc function sequence))
+
+(defalias 'seq-each #'seq-do)
+
+(cl-defgeneric seqp (sequence)
+  "Return non-nil if SEQUENCE is a sequence, nil otherwise."
+  (sequencep sequence))
+
+(cl-defgeneric seq-copy (sequence)
+  "Return a shallow copy of SEQUENCE."
+  (copy-sequence sequence))
+
+(cl-defgeneric seq-subseq (sequence start &optional end)
+  "Return the sequence of elements of SEQUENCE from START to END.
+END is inclusive.
+
+If END is omitted, it defaults to the length of the sequence.  If
+START or END is negative, it counts from the end.  Signal an
+error if START or END are outside of the sequence (i.e too large
+if positive or too small if negative)."
+  (cl-subseq sequence start end))
+
+
+(cl-defgeneric seq-map (function sequence)
+  "Return the result of applying FUNCTION to each element of SEQUENCE."
+  (let (result)
+    (seq-do (lambda (elt)
+              (push (funcall function elt) result))
+            sequence)
+    (nreverse result)))
+
+(defun seq-map-indexed (function sequence)
+  "Return the result of applying FUNCTION to each element of SEQUENCE.
+Unlike `seq-map', FUNCTION takes two arguments: the element of
+the sequence, and its index within the sequence."
+  (let ((index 0))
+    (seq-map (lambda (elt)
+               (prog1
+                   (funcall function elt index)
+                 (setq index (1+ index))))
+             sequence)))
+
+;; faster implementation for sequences (sequencep)
+(cl-defmethod seq-map (function (sequence sequence))
+  (mapcar function sequence))
+
+(cl-defgeneric seq-mapn (function sequence &rest sequences)
+  "Like `seq-map' but FUNCTION is mapped over all SEQUENCES.
+The arity of FUNCTION must match the number of SEQUENCES, and the
+mapping stops on the shortest sequence.
+Return a list of the results.
+
+\(fn FUNCTION SEQUENCES...)"
+  (let ((result nil)
+        (sequences (seq-map (lambda (s) (seq-into s 'list))
+                            (cons sequence sequences))))
+    (while (not (memq nil sequences))
+      (push (apply function (seq-map #'car sequences)) result)
+      (setq sequences (seq-map #'cdr sequences)))
+    (nreverse result)))
+
+(cl-defgeneric seq-drop (sequence n)
+  "Remove the first N elements of SEQUENCE and return the result.
+The result is a sequence of the same type as SEQUENCE.
+
+If N is a negative integer or zero, SEQUENCE is returned."
+  (if (<= n 0)
+      sequence
+    (let ((length (seq-length sequence)))
+      (seq-subseq sequence (min n length) length))))
+
+(cl-defgeneric seq-take (sequence n)
+  "Take the first N elements of SEQUENCE and return the result.
+The result is a sequence of the same type as SEQUENCE.
+
+If N is a negative integer or zero, an empty sequence is
+returned."
+  (seq-subseq sequence 0 (min (max n 0) (seq-length sequence))))
+
+(cl-defgeneric seq-drop-while (pred sequence)
+  "Remove the successive elements of SEQUENCE for which PRED returns non-nil.
+PRED is a function of one argument.  The result is a sequence of
+the same type as SEQUENCE."
+  (seq-drop sequence (seq--count-successive pred sequence)))
+
+(cl-defgeneric seq-take-while (pred sequence)
+  "Take the successive elements of SEQUENCE for which PRED returns non-nil.
+PRED is a function of one argument.  The result is a sequence of
+the same type as SEQUENCE."
+  (seq-take sequence (seq--count-successive pred sequence)))
+
+(cl-defgeneric seq-empty-p (sequence)
+  "Return non-nil if the SEQUENCE is empty, nil otherwise."
+  (= 0 (seq-length sequence)))
+
+(cl-defgeneric seq-sort (pred sequence)
+  "Sort SEQUENCE using PRED as comparison function.
+The result is a sequence of the same type as SEQUENCE."
+  (let ((result (seq-sort pred (append sequence nil))))
+    (seq-into result (type-of sequence))))
+
+(defun seq-sort-by (function pred sequence)
+  "Sort SEQUENCE using PRED as a comparison function.
+Elements of SEQUENCE are transformed by FUNCTION before being
+sorted.  FUNCTION must be a function of one argument."
+  (seq-sort (lambda (a b)
+              (funcall pred
+                       (funcall function a)
+                       (funcall function b)))
+            sequence))
+
+(cl-defmethod seq-sort (pred (list list))
+  (sort (seq-copy list) pred))
+
+(cl-defgeneric seq-reverse (sequence)
+  "Return a sequence with elements of SEQUENCE in reverse order."
+  (let ((result '()))
+    (seq-map (lambda (elt)
+               (push elt result))
+             sequence)
+    (seq-into result (type-of sequence))))
+
+;; faster implementation for sequences (sequencep)
+(cl-defmethod seq-reverse ((sequence sequence))
+  (reverse sequence))
+
+(cl-defgeneric seq-concatenate (type &rest sequences)
+  "Concatenate SEQUENCES into a single sequence of type TYPE.
+TYPE must be one of following symbols: vector, string or list.
+
+\n(fn TYPE SEQUENCE...)"
+  (apply #'cl-concatenate type (seq-map #'seq-into-sequence sequences)))
+
+(cl-defgeneric seq-into-sequence (sequence)
+  "Convert SEQUENCE into a sequence.
+
+The default implementation is to signal an error if SEQUENCE is not a
+sequence, specific functions should be implemented for new types
+of sequence."
+  (unless (sequencep sequence)
+    (error "Cannot convert %S into a sequence" sequence))
+  sequence)
+
+(cl-defgeneric seq-into (sequence type)
+  "Concatenate the elements of SEQUENCE into a sequence of type TYPE.
+TYPE can be one of the following symbols: vector, string or
+list."
+  (pcase type
+    (`vector (vconcat sequence))
+    (`string (concat sequence))
+    (`list (append sequence nil))
+    (_ (error "Not a sequence type name: %S" type))))
+
+(cl-defgeneric seq-filter (pred sequence)
+  "Return a list of all the elements for which (PRED element) is non-nil in SEQUENCE."
+  (let ((exclude (make-symbol "exclude")))
+    (delq exclude (seq-map (lambda (elt)
+                             (if (funcall pred elt)
+                                 elt
+                               exclude))
+                           sequence))))
+
+(cl-defgeneric seq-remove (pred sequence)
+  "Return a list of all the elements for which (PRED element) is nil in SEQUENCE."
+  (seq-filter (lambda (elt) (not (funcall pred elt)))
+              sequence))
+
+(cl-defgeneric seq-reduce (function sequence initial-value)
+  "Reduce the function FUNCTION across SEQUENCE, starting with INITIAL-VALUE.
+
+Return the result of calling FUNCTION with INITIAL-VALUE and the
+first element of SEQUENCE, then calling FUNCTION with that result and
+the second element of SEQUENCE, then with that result and the third
+element of SEQUENCE, etc.
+
+If SEQUENCE is empty, return INITIAL-VALUE and FUNCTION is not called."
+  (if (seq-empty-p sequence)
+      initial-value
+    (let ((acc initial-value))
+      (seq-doseq (elt sequence)
+        (setq acc (funcall function acc elt)))
+      acc)))
+
+(cl-defgeneric seq-every-p (pred sequence)
+  "Return non-nil if (PRED element) is non-nil for all elements of SEQUENCE."
+  (catch 'seq--break
+    (seq-doseq (elt sequence)
+      (or (funcall pred elt)
+          (throw 'seq--break nil)))
+    t))
+
+(cl-defgeneric seq-some (pred sequence)
+  "Return the first value for which if (PRED element) is non-nil for in SEQUENCE."
+  (catch 'seq--break
+    (seq-doseq (elt sequence)
+      (let ((result (funcall pred elt)))
+        (when result
+          (throw 'seq--break result))))
+    nil))
+
+(cl-defgeneric seq-find (pred sequence &optional default)
+  "Return the first element for which (PRED element) is non-nil in SEQUENCE.
+If no element is found, return DEFAULT.
+
+Note that `seq-find' has an ambiguity if the found element is
+identical to DEFAULT, as it cannot be known if an element was
+found or not."
+  (catch 'seq--break
+    (seq-doseq (elt sequence)
+      (when (funcall pred elt)
+        (throw 'seq--break elt)))
+    default))
+
+(cl-defgeneric seq-count (pred sequence)
+  "Return the number of elements for which (PRED element) is non-nil in SEQUENCE."
+  (let ((count 0))
+    (seq-doseq (elt sequence)
+      (when (funcall pred elt)
+        (setq count (+ 1 count))))
+    count))
+
+(cl-defgeneric seq-contains (sequence elt &optional testfn)
+  "Return the first element in SEQUENCE that is equal to ELT.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-some (lambda (e)
+              (funcall (or testfn #'equal) elt e))
+            sequence))
+
+(cl-defgeneric seq-position (sequence elt &optional testfn)
+  "Return the index of the first element in SEQUENCE that is equal to ELT.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (let ((index 0))
+    (catch 'seq--break
+      (seq-doseq (e sequence)
+        (when (funcall (or testfn #'equal) e elt)
+          (throw 'seq--break index))
+        (setq index (1+ index)))
+      nil)))
+
+(cl-defgeneric seq-uniq (sequence &optional testfn)
+  "Return a list of the elements of SEQUENCE with duplicates removed.
+TESTFN is used to compare elements, or `equal' if TESTFN is nil."
+  (let ((result '()))
+    (seq-doseq (elt sequence)
+      (unless (seq-contains result elt testfn)
+        (setq result (cons elt result))))
+    (nreverse result)))
+
+(cl-defgeneric seq-mapcat (function sequence &optional type)
+  "Concatenate the result of applying FUNCTION to each element of SEQUENCE.
+The result is a sequence of type TYPE, or a list if TYPE is nil."
+  (apply #'seq-concatenate (or type 'list)
+         (seq-map function sequence)))
+
+(cl-defgeneric seq-partition (sequence n)
+  "Return a list of the elements of SEQUENCE grouped into sub-sequences of length N.
+The last sequence may contain less than N elements.  If N is a
+negative integer or 0, nil is returned."
+  (unless (< n 1)
+    (let ((result '()))
+      (while (not (seq-empty-p sequence))
+        (push (seq-take sequence n) result)
+        (setq sequence (seq-drop sequence n)))
+      (nreverse result))))
+
+(cl-defgeneric seq-intersection (sequence1 sequence2 &optional testfn)
+  "Return a list of the elements that appear in both SEQUENCE1 and SEQUENCE2.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-reduce (lambda (acc elt)
+                (if (seq-contains sequence2 elt testfn)
+                    (cons elt acc)
+                  acc))
+              (seq-reverse sequence1)
+              '()))
+
+(cl-defgeneric seq-difference (sequence1 sequence2 &optional testfn)
+  "Return a list of the elements that appear in SEQUENCE1 but not in SEQUENCE2.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-reduce (lambda (acc elt)
+                (if (not (seq-contains sequence2 elt testfn))
+                    (cons elt acc)
+                  acc))
+              (seq-reverse sequence1)
+              '()))
+
+(cl-defgeneric seq-group-by (function sequence)
+  "Apply FUNCTION to each element of SEQUENCE.
+Separate the elements of SEQUENCE into an alist using the results as
+keys.  Keys are compared using `equal'."
+  (seq-reduce
+   (lambda (acc elt)
+     (let* ((key (funcall function elt))
+            (cell (assoc key acc)))
+       (if cell
+           (setcdr cell (push elt (cdr cell)))
+         (push (list key elt) acc))
+       acc))
+   (seq-reverse sequence)
+   nil))
+
+(cl-defgeneric seq-min (sequence)
+  "Return the smallest element of SEQUENCE.
+SEQUENCE must be a sequence of numbers or markers."
+  (apply #'min (seq-into sequence 'list)))
+
+(cl-defgeneric seq-max (sequence)
+  "Return the largest element of SEQUENCE.
+SEQUENCE must be a sequence of numbers or markers."
+  (apply #'max (seq-into sequence 'list)))
+
+(defun seq--count-successive (pred sequence)
+  "Return the number of successive elements for which (PRED element) is non-nil in SEQUENCE."
+  (let ((n 0)
+        (len (seq-length sequence)))
+    (while (and (< n len)
+                (funcall pred (seq-elt sequence n)))
+      (setq n (+ 1 n)))
+    n))
+
+;;; Optimized implementations for lists
+
+(cl-defmethod seq-drop ((list list) n)
+  "Optimized implementation of `seq-drop' for lists."
+  (nthcdr n list))
+
+(cl-defmethod seq-take ((list list) n)
+  "Optimized implementation of `seq-take' for lists."
+  (let ((result '()))
+    (while (and list (> n 0))
+      (setq n (1- n))
+      (push (pop list) result))
+    (nreverse result)))
+
+(cl-defmethod seq-drop-while (pred (list list))
+  "Optimized implementation of `seq-drop-while' for lists."
+  (while (and list (funcall pred (car list)))
+    (setq list (cdr list)))
+  list)
+
+(cl-defmethod seq-empty-p ((list list))
+  "Optimized implementation of `seq-empty-p' for lists."
+  (null list))
+
+
+(defun seq--make-pcase-bindings (args)
+  "Return a list of bindings of the variables in ARGS to the elements of a sequence."
+  (let ((bindings '())
+        (index 0)
+        (rest-marker nil))
+    (seq-doseq (name args)
+      (unless rest-marker
+        (pcase name
+          (`&rest
+           (progn (push `(app (pcase--flip seq-drop ,index)
+                              ,(seq--elt-safe args (1+ index)))
+                        bindings)
+                  (setq rest-marker t)))
+          (_
+           (push `(app (pcase--flip seq--elt-safe ,index) ,name) bindings))))
+      (setq index (1+ index)))
+    bindings))
+
+(defun seq--make-pcase-patterns (args)
+  "Return a list of `(seq ...)' pcase patterns from the argument list ARGS."
+  (cons 'seq
+        (seq-map (lambda (elt)
+                   (if (seqp elt)
+                       (seq--make-pcase-patterns elt)
+                     elt))
+                 args)))
+
+;; TODO: make public?
+(defun seq--elt-safe (sequence n)
+  "Return element of SEQUENCE at the index N.
+If no element is found, return nil."
+  (ignore-errors (seq-elt sequence n))))
+
+(provide 'seq-25)
+;;; seq-25.el ends here