emacs/lisp/emacs-lisp/subr-x.el

;;; subr-x.el --- extra Lisp functions  -*- lexical-binding:t -*-

;; Copyright (C) 2013-2016 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:

(require 'pcase)


(defmacro internal--thread-argument (first? &rest forms)
  "Internal implementation for `thread-first' and `thread-last'.
When Argument FIRST? is non-nil argument is threaded first, else
last.  FORMS are the expressions to be threaded."
  (pcase forms
    (`(,x (,f . ,args) . ,rest)
     `(internal--thread-argument
       ,first? ,(if first? `(,f ,x ,@args) `(,f ,@args ,x)) ,@rest))
    (`(,x ,f . ,rest) `(internal--thread-argument ,first? (,f ,x) ,@rest))
    (_ (car forms))))

(defmacro thread-first (&rest forms)
  "Thread FORMS elements as the first argument of their successor.
Example:
    (thread-first
      5
      (+ 20)
      (/ 25)
      -
      (+ 40))
Is equivalent to:
    (+ (- (/ (+ 5 20) 25)) 40)
Note how the single `-' got converted into a list before
threading."
  (declare (indent 1)
           (debug (form &rest [&or symbolp (sexp &rest form)])))
  `(internal--thread-argument t ,@forms))

(defmacro thread-last (&rest forms)
  "Thread FORMS elements as the last argument of their successor.
Example:
    (thread-last
      5
      (+ 20)
      (/ 25)
      -
      (+ 40))
Is equivalent to:
    (+ 40 (- (/ 25 (+ 20 5))))
Note how the single `-' got converted into a list before
threading."
  (declare (indent 1) (debug thread-first))
  `(internal--thread-argument nil ,@forms))

(defsubst internal--listify (elt)
  "Wrap ELT in a list if it is not one."
  (if (not (listp elt))
      (list elt)
    elt))

(defsubst internal--check-binding (binding)
  "Check BINDING is properly formed."
  (when (> (length binding) 2)
    (signal
     'error
     (cons "`let' bindings can have only one value-form" binding)))
  binding)

(defsubst internal--build-binding-value-form (binding prev-var)
  "Build the conditional value form for BINDING using PREV-VAR."
  `(,(car binding) (and ,prev-var ,(cadr binding))))

(defun internal--build-binding (binding prev-var)
  "Check and build a single BINDING with PREV-VAR."
  (thread-first
      binding
    internal--listify
    internal--check-binding
    (internal--build-binding-value-form prev-var)))

(defun internal--build-bindings (bindings)
  "Check and build conditional value forms for BINDINGS."
  (let ((prev-var t))
    (mapcar (lambda (binding)
              (let ((binding (internal--build-binding binding prev-var)))
                (setq prev-var (car binding))
                binding))
            bindings)))

(defmacro if-let (bindings then &rest else)
  "Process BINDINGS and if all values are non-nil eval THEN, else ELSE.
Argument BINDINGS is a list of tuples whose car is a symbol to be
bound and (optionally) used in THEN, and its cadr is a sexp to be
evalled to set symbol's value.  In the special case you only want
to bind a single value, BINDINGS can just be a plain tuple."
  (declare (indent 2)
           (debug ([&or (&rest (symbolp form)) (symbolp form)] form body)))
  (when (and (<= (length bindings) 2)
             (not (listp (car bindings))))
    ;; Adjust the single binding case
    (setq bindings (list bindings)))
  `(let* ,(internal--build-bindings bindings)
     (if ,(car (internal--listify (car (last bindings))))
         ,then
       ,@else)))

(defmacro when-let (bindings &rest body)
  "Process BINDINGS and if all values are non-nil eval BODY.
Argument BINDINGS is a list of tuples whose car is a symbol to be
bound and (optionally) used in BODY, and its cadr is a sexp to be
evalled to set symbol's value.  In the special case you only want
to bind a single value, BINDINGS can just be a plain tuple."
  (declare (indent 1) (debug if-let))
  (list 'if-let bindings (macroexp-progn body)))

(defsubst hash-table-empty-p (hash-table)
  "Check whether HASH-TABLE is empty (has 0 elements)."
  (zerop (hash-table-count hash-table)))

(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))

(define-obsolete-function-alias 'string-reverse 'reverse "25.1")

(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