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+;;; subr-x.el --- extra Lisp functions  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2013-2014 Free Software Foundation, Inc.
+
+;; Maintainer: emacs-devel@gnu.org
+;; Keywords: convenience
+;; Package: emacs
+
+;; 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:
+
+;; Less commonly used functions that complement basic APIs, often implemented in
+;; C code (like hash-tables and strings), and are not eligible for inclusion
+;; in subr.el.
+
+;; Do not document these functions in the lispref.
+;; http://lists.gnu.org/archive/html/emacs-devel/2014-01/msg01006.html
+
+;;; Code:
+
+(defsubst hash-table-keys (hash-table)
+  "Return a list of keys in HASH-TABLE."
+  (let ((keys '()))
+    (maphash (lambda (k _v) (push k keys)) hash-table)
+    keys))
+
+(defsubst hash-table-values (hash-table)
+  "Return a list of values in HASH-TABLE."
+  (let ((values '()))
+    (maphash (lambda (_k v) (push v values)) hash-table)
+    values))
+
+(defsubst string-empty-p (string)
+  "Check whether STRING is empty."
+  (string= string ""))
+
+(defsubst string-join (strings &optional separator)
+  "Join all STRINGS using SEPARATOR."
+  (mapconcat 'identity strings separator))
+
+(defsubst string-reverse (str)
+  "Reverse the string STR."
+  (apply 'string (nreverse (string-to-list str))))
+
+(defsubst string-trim-left (string)
+  "Remove leading whitespace from STRING."
+  (if (string-match "\\`[ \t\n\r]+" string)
+      (replace-match "" t t string)
+    string))
+
+(defsubst string-trim-right (string)
+  "Remove trailing whitespace from STRING."
+  (if (string-match "[ \t\n\r]+\\'" string)
+      (replace-match "" t t string)
+    string))
+
+(defsubst string-trim (string)
+  "Remove leading and trailing whitespace from STRING."
+  (string-trim-left (string-trim-right string)))
+
+(defsubst string-blank-p (string)
+  "Check whether STRING is either empty or only whitespace."
+  (string-match-p "\\`[ \t\n\r]*\\'" string))
+
+(defsubst string-remove-prefix (prefix string)
+  "Remove PREFIX from STRING if present."
+  (if (string-prefix-p prefix string)
+      (substring string (length prefix))
+    string))
+
+(defsubst string-remove-suffix (suffix string)
+  "Remove SUFFIX from STRING if present."
+  (if (string-suffix-p suffix string)
+      (substring string 0 (- (length string) (length suffix)))
+    string))
+
+(provide 'subr-x)
+
+;;; subr-x.el ends here