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+;;; seq.el --- Sequence manipulation functions  -*- lexical-binding: t -*-
+
+;; Copyright (C) 2014-2015 Free Software Foundation, Inc.
+
+;; Author: Nicolas Petton <nicolas@petton.fr>
+;; Keywords: sequences
+;; Version: 1.2
+
+;; 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 a function iterating over the
+;; sequence 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.
+;;
+;; All functions are tested in test/automated/seq-tests.el
+
+;;; Code:
+
+(defmacro seq-doseq (spec &rest body)
+  "Loop over a sequence.
+Similar to `dolist' but can be applied lists, strings and vectors.
+
+Evaluate BODY with VAR bound to each element of SEQ, in turn.
+Then evaluate RESULT to get return value, default nil.
+
+\(fn (VAR SEQ [RESULT]) BODY...)"
+  (declare (indent 1) (debug ((symbolp form &optional form) body)))
+  (let ((is-list (make-symbol "is-list"))
+        (seq (make-symbol "seq"))
+        (index (make-symbol "index")))
+    `(let* ((,seq ,(cadr spec))
+            (,is-list (listp ,seq))
+            (,index (if ,is-list ,seq 0)))
+       (while (if ,is-list
+                  (consp ,index)
+                (< ,index (seq-length ,seq)))
+         (let ((,(car spec) (if ,is-list
+                                (car ,index)
+                              (seq-elt ,seq ,index))))
+           ,@body
+           (setq ,index (if ,is-list
+                            (cdr ,index)
+                          (+ ,index 1)))))
+       ,@(if (cddr spec)
+             `((setq ,(car spec) nil) ,@(cddr spec))))))
+
+(defun seq-drop (seq n)
+  "Return a subsequence of SEQ without its first N elements.
+The result is a sequence of the same type as SEQ.
+
+If N is a negative integer or zero, SEQ is returned."
+  (if (<= n 0)
+      seq
+    (if (listp seq)
+        (seq--drop-list seq n)
+      (let ((length (seq-length seq)))
+        (seq-subseq seq (min n length) length)))))
+
+(defun seq-take (seq n)
+  "Return a subsequence of SEQ with its first N elements.
+The result is a sequence of the same type as SEQ.
+
+If N is a negative integer or zero, an empty sequence is
+returned."
+  (if (listp seq)
+      (seq--take-list seq n)
+    (seq-subseq seq 0 (min (max n 0) (seq-length seq)))))
+
+(defun seq-drop-while (pred seq)
+  "Return a sequence from the first element for which (PRED element) is nil in SEQ.
+The result is a sequence of the same type as SEQ."
+  (if (listp seq)
+      (seq--drop-while-list pred seq)
+    (seq-drop seq (seq--count-successive pred seq))))
+
+(defun seq-take-while (pred seq)
+  "Return the successive elements for which (PRED element) is non-nil in SEQ.
+The result is a sequence of the same type as SEQ."
+  (if (listp seq)
+      (seq--take-while-list pred seq)
+    (seq-take seq (seq--count-successive pred seq))))
+
+(defun seq-filter (pred seq)
+  "Return a list of all the elements for which (PRED element) is non-nil in SEQ."
+  (let ((exclude (make-symbol "exclude")))
+    (delq exclude (seq-map (lambda (elt)
+                             (if (funcall pred elt)
+                                 elt
+                               exclude))
+                           seq))))
+
+(defun seq-remove (pred seq)
+  "Return a list of all the elements for which (PRED element) is nil in SEQ."
+  (seq-filter (lambda (elt) (not (funcall pred elt)))
+              seq))
+
+(defun seq-reduce (function seq initial-value)
+  "Reduce the function FUNCTION across SEQ, starting with INITIAL-VALUE.
+
+Return the result of calling FUNCTION with INITIAL-VALUE and the
+first element of SEQ, then calling FUNCTION with that result and
+the second element of SEQ, then with that result and the third
+element of SEQ, etc.
+
+If SEQ is empty, return INITIAL-VALUE and FUNCTION is not called."
+  (if (seq-empty-p seq)
+      initial-value
+    (let ((acc initial-value))
+      (seq-doseq (elt seq)
+        (setq acc (funcall function acc elt)))
+      acc)))
+
+(defun seq-some-p (pred seq)
+  "Return any element for which (PRED element) is non-nil in SEQ, nil otherwise."
+  (catch 'seq--break
+    (seq-doseq (elt seq)
+      (when (funcall pred elt)
+        (throw 'seq--break elt)))
+    nil))
+
+(defun seq-every-p (pred seq)
+  "Return non-nil if (PRED element) is non-nil for all elements of the sequence SEQ."
+  (catch 'seq--break
+    (seq-doseq (elt seq)
+      (or (funcall pred elt)
+          (throw 'seq--break nil)))
+    t))
+
+(defun seq-count (pred seq)
+  "Return the number of elements for which (PRED element) is non-nil in SEQ."
+  (let ((count 0))
+    (seq-doseq (elt seq)
+      (when (funcall pred elt)
+        (setq count (+ 1 count))))
+    count))
+
+(defun seq-empty-p (seq)
+  "Return non-nil if the sequence SEQ is empty, nil otherwise."
+  (if (listp seq)
+      (null seq)
+    (= 0 (seq-length seq))))
+
+(defun seq-sort (pred seq)
+  "Return a sorted sequence comparing using PRED the elements of SEQ.
+The result is a sequence of the same type as SEQ."
+  (if (listp seq)
+      (sort (seq-copy seq) pred)
+    (let ((result (seq-sort pred (append seq nil))))
+      (seq--into result (type-of seq)))))
+
+(defun seq-contains-p (seq elt &optional testfn)
+  "Return the first element in SEQ that equals to ELT.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-some-p (lambda (e)
+                (funcall (or testfn #'equal) elt e))
+              seq))
+
+(defun seq-uniq (seq &optional testfn)
+  "Return a list of the elements of SEQ with duplicates removed.
+TESTFN is used to compare elements, or `equal' if TESTFN is nil."
+  (let ((result '()))
+    (seq-doseq (elt seq)
+      (unless (seq-contains-p result elt testfn)
+        (setq result (cons elt result))))
+    (nreverse result)))
+
+(defun seq-subseq (seq start &optional end)
+  "Return the subsequence of SEQ from START to END.
+If END is omitted, it defaults to the length of the sequence.
+If START or END is negative, it counts from the end."
+  (cond ((or (stringp seq) (vectorp seq)) (substring seq start end))
+        ((listp seq)
+         (let (len (errtext (format "Bad bounding indices: %s, %s" start end)))
+           (and end (< end 0) (setq end (+ end (setq len (seq-length seq)))))
+           (if (< start 0) (setq start (+ start (or len (setq len (seq-length seq))))))
+           (when (> start 0)
+             (setq seq (nthcdr (1- start) seq))
+             (or seq (error "%s" errtext))
+             (setq seq (cdr seq)))
+           (if end
+               (let ((res nil))
+                 (while (and (>= (setq end (1- end)) start) seq)
+                   (push (pop seq) res))
+                 (or (= (1+ end) start) (error "%s" errtext))
+                 (nreverse res))
+             (seq-copy seq))))
+        (t (error "Unsupported sequence: %s" seq))))
+
+(defun seq-concatenate (type &rest seqs)
+  "Concatenate, into a sequence of type TYPE, the sequences SEQS.
+TYPE must be one of following symbols: vector, string or list.
+
+\n(fn TYPE SEQUENCE...)"
+  (pcase type
+    (`vector (apply #'vconcat seqs))
+    (`string (apply #'concat seqs))
+    (`list (apply #'append (append seqs '(nil))))
+    (t (error "Not a sequence type name: %s" type))))
+
+(defun seq-mapcat (function seq &optional type)
+  "Concatenate the result of applying FUNCTION to each element of SEQ.
+The result is a sequence of type TYPE, or a list if TYPE is nil."
+  (apply #'seq-concatenate (or type 'list)
+         (seq-map function seq)))
+
+(defun seq-partition (seq n)
+  "Return a list of the elements of SEQ 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 seq))
+        (push (seq-take seq n) result)
+        (setq seq (seq-drop seq n)))
+      (nreverse result))))
+
+(defun seq-group-by (function seq)
+  "Apply FUNCTION to each element of SEQ.
+Separate the elements of SEQ 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 seq)
+   nil))
+
+(defalias 'seq-reverse
+  (if (ignore-errors (reverse [1 2]))
+      #'reverse
+    (lambda (seq)
+      "Return the reversed copy of list, vector, or string SEQ.
+See also the function `nreverse', which is used more often."
+      (let ((result '()))
+        (seq-map (lambda (elt) (push elt result))
+                 seq)
+        (if (listp seq)
+            result
+          (seq--into result (type-of seq)))))))
+
+(defun seq--into (seq type)
+  "Convert the sequence SEQ into a sequence of type TYPE."
+  (pcase type
+    (`vector (vconcat seq))
+    (`string (concat seq))
+    (`list (append seq nil))
+    (t (error "Not a sequence type name: %s" type))))
+
+(defun seq--drop-list (list n)
+  "Return a list from LIST without its first N elements.
+This is an optimization for lists in `seq-drop'."
+  (while (and list (> n 0))
+    (setq list (cdr list)
+          n (1- n)))
+  list)
+
+(defun seq--take-list (list n)
+  "Return a list from LIST made of its first N elements.
+This is an optimization for lists in `seq-take'."
+  (let ((result '()))
+    (while (and list (> n 0))
+      (setq n (1- n))
+      (push (pop list) result))
+    (nreverse result)))
+
+(defun seq--drop-while-list (pred list)
+  "Return a list from the first element for which (PRED element) is nil in LIST.
+This is an optimization for lists in `seq-drop-while'."
+  (while (and list (funcall pred (car list)))
+    (setq list (cdr list)))
+  list)
+
+(defun seq--take-while-list (pred list)
+  "Return the successive elements for which (PRED element) is non-nil in LIST.
+This is an optimization for lists in `seq-take-while'."
+  (let ((result '()))
+    (while (and list (funcall pred (car list)))
+      (push (pop list) result))
+    (nreverse result)))
+
+(defun seq--count-successive (pred seq)
+  "Return the number of successive elements for which (PRED element) is non-nil in SEQ."
+  (let ((n 0)
+        (len (seq-length seq)))
+    (while (and (< n len)
+                (funcall pred (seq-elt seq n)))
+      (setq n (+ 1 n)))
+    n))
+
+(defalias 'seq-copy #'copy-sequence)
+(defalias 'seq-elt #'elt)
+(defalias 'seq-length #'length)
+(defalias 'seq-do #'mapc)
+(defalias 'seq-each #'seq-do)
+(defalias 'seq-map #'mapcar)
+
+(provide 'seq)
+;;; seq.el ends here