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150 lines
5.3 KiB
EmacsLisp
150 lines
5.3 KiB
EmacsLisp
;;; format-spec.el --- functions for formatting arbitrary formatting strings
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;; Copyright (C) 1999-2020 Free Software Foundation, Inc.
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;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
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;; Keywords: tools
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;;; Code:
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(eval-when-compile
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(require 'subr-x))
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(defun format-spec (format specification &optional only-present)
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"Return a string based on FORMAT and SPECIFICATION.
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FORMAT is a string containing `format'-like specs like \"su - %u %k\",
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while SPECIFICATION is an alist mapping from format spec characters
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to values.
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For instance:
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(format-spec \"su - %u %l\"
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`((?u . ,(user-login-name))
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(?l . \"ls\")))
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Each format spec can have modifiers, where \"%<010b\" means \"if
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the expansion is shorter than ten characters, zero-pad it, and if
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it's longer, chop off characters from the left side\".
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The following modifiers are allowed:
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* 0: Use zero-padding.
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* -: Pad to the right.
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* ^: Upper-case the expansion.
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* _: Lower-case the expansion.
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* <: Limit the length by removing chars from the left.
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* >: Limit the length by removing chars from the right.
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Any text properties on a %-spec itself are propagated to the text
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that it generates.
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If ONLY-PRESENT, format spec characters not present in
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SPECIFICATION are ignored, and the \"%\" characters are left
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where they are, including \"%%\" strings."
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(with-temp-buffer
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(insert format)
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(goto-char (point-min))
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(while (search-forward "%" nil t)
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(cond
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;; Quoted percent sign.
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((eq (char-after) ?%)
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(unless only-present
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(delete-char 1)))
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;; Valid format spec.
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((looking-at "\\([-0 _^<>]*\\)\\([0-9.]*\\)\\([a-zA-Z]\\)")
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(let* ((modifiers (match-string 1))
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(num (match-string 2))
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(spec (string-to-char (match-string 3)))
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(val (assq spec specification)))
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(if (not val)
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(unless only-present
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(error "Invalid format character: `%%%c'" spec))
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(setq val (cdr val)
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modifiers (format-spec--parse-modifiers modifiers))
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;; Pad result to desired length.
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(let ((text (format "%s" val)))
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(when num
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(setq num (string-to-number num))
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(setq text (format-spec--pad text num modifiers))
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(when (> (length text) num)
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(cond
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((memq :chop-left modifiers)
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(setq text (substring text (- (length text) num))))
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((memq :chop-right modifiers)
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(setq text (substring text 0 num))))))
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(when (memq :uppercase modifiers)
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(setq text (upcase text)))
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(when (memq :lowercase modifiers)
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(setq text (downcase text)))
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;; Insert first, to preserve text properties.
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(insert-and-inherit text)
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;; Delete the specifier body.
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(delete-region (+ (match-beginning 0) (length text))
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(+ (match-end 0) (length text)))
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;; Delete the percent sign.
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(delete-region (1- (match-beginning 0)) (match-beginning 0))))))
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;; Signal an error on bogus format strings.
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(t
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(unless only-present
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(error "Invalid format string")))))
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(buffer-string)))
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(defun format-spec--pad (text total-length modifiers)
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(if (> (length text) total-length)
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;; The text is longer than the specified length; do nothing.
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text
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(let ((padding (make-string (- total-length (length text))
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(if (memq :zero-pad modifiers)
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?0
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?\s))))
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(if (memq :right-pad modifiers)
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(concat text padding)
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(concat padding text)))))
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(defun format-spec--parse-modifiers (modifiers)
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(mapcan (lambda (char)
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(when-let ((modifier
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(pcase char
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(?0 :zero-pad)
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(?\s :space-pad)
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(?^ :uppercase)
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(?_ :lowercase)
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(?- :right-pad)
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(?< :chop-left)
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(?> :chop-right))))
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(list modifier)))
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modifiers))
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(defun format-spec-make (&rest pairs)
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"Return an alist suitable for use in `format-spec' based on PAIRS.
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PAIRS is a list where every other element is a character and a value,
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starting with a character."
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(let (alist)
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(while pairs
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(unless (cdr pairs)
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(error "Invalid list of pairs"))
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(push (cons (car pairs) (cadr pairs)) alist)
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(setq pairs (cddr pairs)))
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(nreverse alist)))
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(provide 'format-spec)
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;;; format-spec.el ends here
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