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

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

;; Copyright (C) 2013-2021 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 <https://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.
;; https://lists.gnu.org/r/emacs-devel/2014-01/msg01006.html

;; NB If you want to use this library, it's almost always correct to use:
;; (eval-when-compile (require 'subr-x))

;;; Code:

(eval-when-compile (require 'cl-lib))


(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 0)
           (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 0) (debug thread-first))
  `(internal--thread-argument nil ,@forms))

(defsubst internal--listify (elt)
  "Wrap ELT in a list if it is not one.
If ELT is of the form ((EXPR)), listify (EXPR) with a dummy symbol."
  (cond
   ((symbolp elt) (list elt elt))
   ((null (cdr elt))
    (list (make-symbol "s") (car elt)))
   (t 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."
  (let ((var (car binding)))
    `(,var (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* (varlist then &rest else)
  "Bind variables according to VARLIST and evaluate THEN or ELSE.
This is like `if-let' but doesn't handle a VARLIST of the form
\(SYMBOL SOMETHING) specially."
  (declare (indent 2)
           (debug ((&rest [&or symbolp (symbolp form) (form)])
                   body)))
  (if varlist
      `(let* ,(setq varlist (internal--build-bindings varlist))
         (if ,(caar (last varlist))
             ,then
           ,@else))
    `(let* () ,then)))

(defmacro when-let* (varlist &rest body)
  "Bind variables according to VARLIST and conditionally evaluate BODY.
This is like `when-let' but doesn't handle a VARLIST of the form
\(SYMBOL SOMETHING) specially."
  (declare (indent 1) (debug if-let*))
  (list 'if-let* varlist (macroexp-progn body)))

(defmacro and-let* (varlist &rest body)
  "Bind variables according to VARLIST and conditionally evaluate BODY.
Like `when-let*', except if BODY is empty and all the bindings
are non-nil, then the result is non-nil."
  (declare (indent 1) (debug if-let*))
  (let (res)
    (if varlist
        `(let* ,(setq varlist (internal--build-bindings varlist))
           (when ,(setq res (caar (last varlist)))
             ,@(or body `(,res))))
      `(let* () ,@(or body '(t))))))

;;;###autoload
(defmacro if-let (spec then &rest else)
  "Bind variables according to SPEC and evaluate THEN or ELSE.
Evaluate each binding in turn, as in `let*', stopping if a
binding value is nil.  If all are non-nil return the value of
THEN, otherwise the last form in ELSE.

Each element of SPEC is a list (SYMBOL VALUEFORM) that binds
SYMBOL to the value of VALUEFORM.  An element can additionally be
of the form (VALUEFORM), which is evaluated and checked for nil;
i.e. SYMBOL can be omitted if only the test result is of
interest.  It can also be of the form SYMBOL, then the binding of
SYMBOL is checked for nil.

As a special case, interprets a SPEC of the form \(SYMBOL SOMETHING)
like \((SYMBOL SOMETHING)).  This exists for backward compatibility
with an old syntax that accepted only one binding."
  (declare (indent 2)
           (debug ([&or (symbolp form)  ; must be first, Bug#48489
                        (&rest [&or symbolp (symbolp form) (form)])]
                   body)))
  (when (and (<= (length spec) 2)
             (not (listp (car spec))))
    ;; Adjust the single binding case
    (setq spec (list spec)))
  (list 'if-let* spec then (macroexp-progn else)))

;;;###autoload
(defmacro when-let (spec &rest body)
  "Bind variables according to SPEC and conditionally evaluate BODY.
Evaluate each binding in turn, stopping if a binding value is nil.
If all are non-nil, return the value of the last form in BODY.

The variable list SPEC is the same as in `if-let'."
  (declare (indent 1) (debug if-let))
  (list 'if-let spec (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."
  (cl-loop for k being the hash-keys of hash-table collect k))

(defsubst hash-table-values (hash-table)
  "Return a list of values in HASH-TABLE."
  (cl-loop for v being the hash-values of hash-table collect v))

(defsubst string-empty-p (string)
  "Check whether STRING is empty."
  (string= string ""))

(defsubst string-join (strings &optional separator)
  "Join all STRINGS using SEPARATOR.
Optional argument SEPARATOR must be a string, a vector, or a list of
characters; nil stands for the empty string."
  (mapconcat #'identity strings separator))

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

;;;###autoload
(defun string-truncate-left (string length)
  "Truncate STRING to LENGTH, replacing initial surplus with \"...\"."
  (let ((strlen (length string)))
    (if (<= strlen length)
	string
      (setq length (max 0 (- length 3)))
      (concat "..." (substring string (max 0 (- strlen 1 length)))))))

(defsubst string-blank-p (string)
  "Check whether STRING is either empty or only whitespace.
The following characters count as whitespace here: space, tab, newline and
carriage return."
  (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))

;;;###autoload
(defun string-clean-whitespace (string)
  "Clean up whitespace in STRING.
All sequences of whitespaces in STRING are collapsed into a
single space character, and leading/trailing whitespace is
removed."
  (let ((blank "[[:blank:]\r\n]+"))
    (string-trim (replace-regexp-in-string blank " " string t t)
                 blank blank)))

(defun string-fill (string length)
  "Try to word-wrap STRING so that no lines are longer than LENGTH.
Wrapping is done where there is whitespace.  If there are
individual words in STRING that are longer than LENGTH, the
result will have lines that are longer than LENGTH."
  (with-temp-buffer
    (insert string)
    (goto-char (point-min))
    (let ((fill-column length)
          (adaptive-fill-mode nil))
      (fill-region (point-min) (point-max)))
    (buffer-string)))

(defun string-limit (string length &optional end coding-system)
  "Return (up to) a LENGTH substring of STRING.
If STRING is shorter than or equal to LENGTH, the entire string
is returned unchanged.

If STRING is longer than LENGTH, return a substring consisting of
the first LENGTH characters of STRING.  If END is non-nil, return
the last LENGTH characters instead.

If CODING-SYSTEM is non-nil, STRING will be encoded before
limiting, and LENGTH is interpreted as the number of bytes to
limit the string to.  The result will be a unibyte string that is
shorter than LENGTH, but will not contain \"partial\" characters,
even if CODING-SYSTEM encodes characters with several bytes per
character.

When shortening strings for display purposes,
`truncate-string-to-width' is almost always a better alternative
than this function."
  (unless (natnump length)
    (signal 'wrong-type-argument (list 'natnump length)))
  (if coding-system
      (let ((result nil)
            (result-length 0)
            (index (if end (1- (length string)) 0)))
        ;; FIXME: This implementation, which uses encode-coding-char
        ;; to encode the string one character at a time, is in general
        ;; incorrect: coding-systems that produce prefix or suffix
        ;; bytes, such as ISO-2022-based or UTF-8/16 with BOM, will
        ;; produce those bytes for each character, instead of just
        ;; once for the entire string.  encode-coding-char attempts to
        ;; remove those extra bytes at least in some situations, but
        ;; it cannot do that in all cases.  And in any case, producing
        ;; what is supposed to be a UTF-16 or ISO-2022-CN encoded
        ;; string which lacks the BOM bytes at the beginning and the
        ;; charset designation sequences at the head and tail of the
        ;; result will definitely surprise the callers in some cases.
        (while (let ((encoded (encode-coding-char
                               (aref string index) coding-system)))
                 (and (<= (+ (length encoded) result-length) length)
                      (progn
                        (push encoded result)
                        (cl-incf result-length (length encoded))
                        (setq index (if end (1- index)
                                      (1+ index))))
                      (if end (> index -1)
                        (< index (length string)))))
          ;; No body.
          )
        (apply #'concat (if end result (nreverse result))))
    (cond
     ((<= (length string) length) string)
     (end (substring string (- (length string) length)))
     (t (substring string 0 length)))))

;;;###autoload
(defun string-lines (string &optional omit-nulls)
  "Split STRING into a list of lines.
If OMIT-NULLS, empty lines will be removed from the results."
  (split-string string "\n" omit-nulls))

(defun string-pad (string length &optional padding start)
  "Pad STRING to LENGTH using PADDING.
If PADDING is nil, the space character is used.  If not nil, it
should be a character.

If STRING is longer than the absolute value of LENGTH, no padding
is done.

If START is nil (or not present), the padding is done to the end
of the string, and if non-nil, padding is done to the start of
the string."
  (unless (natnump length)
    (signal 'wrong-type-argument (list 'natnump length)))
  (let ((pad-length (- length (length string))))
    (if (< pad-length 0)
        string
      (concat (and start
                   (make-string pad-length (or padding ?\s)))
              string
              (and (not start)
                   (make-string pad-length (or padding ?\s)))))))

(defun string-chop-newline (string)
  "Remove the final newline (if any) from STRING."
  (string-remove-suffix "\n" string))

(defun replace-region-contents (beg end replace-fn
                                    &optional max-secs max-costs)
  "Replace the region between BEG and END using REPLACE-FN.
REPLACE-FN runs on the current buffer narrowed to the region.  It
should return either a string or a buffer replacing the region.

The replacement is performed using `replace-buffer-contents'
which also describes the MAX-SECS and MAX-COSTS arguments and the
return value.

Note: If the replacement is a string, it'll be placed in a
temporary buffer so that `replace-buffer-contents' can operate on
it.  Therefore, if you already have the replacement in a buffer,
it makes no sense to convert it to a string using
`buffer-substring' or similar."
  (save-excursion
    (save-restriction
      (narrow-to-region beg end)
      (goto-char (point-min))
      (let ((repl (funcall replace-fn)))
	(if (bufferp repl)
	    (replace-buffer-contents repl max-secs max-costs)
	  (let ((source-buffer (current-buffer)))
	    (with-temp-buffer
	      (insert repl)
	      (let ((tmp-buffer (current-buffer)))
		(set-buffer source-buffer)
		(replace-buffer-contents tmp-buffer max-secs max-costs)))))))))

(defmacro named-let (name bindings &rest body)
  "Looping construct taken from Scheme.
Like `let', bind variables in BINDINGS and then evaluate BODY,
but with the twist that BODY can evaluate itself recursively by
calling NAME, where the arguments passed to NAME are used
as the new values of the bound variables in the recursive invocation."
  (declare (indent 2) (debug (symbolp (&rest (symbolp form)) body)))
  (require 'cl-lib)
  (let ((fargs (mapcar (lambda (b) (if (consp b) (car b) b)) bindings))
        (aargs (mapcar (lambda (b) (if (consp b) (cadr b))) bindings)))
    ;; According to the Scheme semantics of named let, `name' is not in scope
    ;; while evaluating the expressions in `bindings', and for this reason, the
    ;; "initial" function call below needs to be outside of the `cl-labels'.
    ;; When the "self-tco" eliminates all recursive calls, the `cl-labels'
    ;; expands to a lambda which the byte-compiler then combines with the
    ;; funcall to make a `let' so we end up with a plain `while' loop and no
    ;; remaining `lambda' at all.
    `(funcall
      (cl-labels ((,name ,fargs . ,body)) #',name)
      . ,aargs)))

(defmacro with-memoization (place &rest code)
  "Return the value of CODE and stash it in PLACE.
If PLACE's value is non-nil, then don't bother evaluating CODE
and return the value found in PLACE instead."
  (declare (indent 1) (debug (gv-place body)))
  (gv-letplace (getter setter) place
    `(or ,getter
         ,(macroexp-let2 nil val (macroexp-progn code)
            `(progn
               ,(funcall setter val)
               ,val)))))

;;;###autoload
(defun ensure-empty-lines (&optional lines)
  "Ensure that there's LINES number of empty lines before point.
If LINES is nil or missing, a this ensures that there's a single
empty line before point.

Interactively, this command uses the numerical prefix for LINES.

If there's already more empty lines before point than LINES, the
number of blank lines will be reduced.

If point is not at the beginning of a line, a newline character
is inserted before adjusting the number of empty lines."
  (interactive "p")
  (unless (bolp)
    (insert "\n"))
  (let ((lines (or lines 1))
        (start (save-excursion
                 (if (re-search-backward "[^\n]" nil t)
                     (+ (point) 2)
                   (point-min)))))
    (cond
     ((> (- (point) start) lines)
      (delete-region (point) (- (point) (- (point) start lines))))
     ((< (- (point) start) lines)
      (insert (make-string (- lines (- (point) start)) ?\n))))))

(provide 'subr-x)

;;; subr-x.el ends here