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+++ README.md
+# algol-mode
+
+This is an improved and modernised version of algol68 mode by Jose
+E. Marchesi.
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+++ algol-mode.el
+;;; a68-mode.el --- Major mode for editing Algol 68 code
+
+;; Copyright (C) 2011 Jose E. Marchesi
+
+;; Maintainer: Jose E. Marchesi
+
+;; This file is NOT part of GNU Emacs.
+
+;; This program 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, or (at your option)
+;; any later version.
+
+;; This program 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 this program; see the file COPYING. If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
+
+;;; Commentary:
+
+;; A major mode for editing Algol 68 code.
+;;
+;; TODO: support quote and dot stropping.
+
+;;; Code:
+
+(require 'syntax)
+(require 'font-lock)
+
+(defvar a68-indent-step 3
+ "Indentation step for Algol 68")
+
+(defvar a68-mode-hook nil)
+
+(defvar a68-mode-map
+ (let ((map (make-keymap)))
+ (define-key map "\C-j" 'newline-and-indent)
+ (define-key map "\r" 'electric-a68-terminate-line)
+ (define-key map "\t" 'electric-a68-tab)
+ map)
+ "Keymap for Algol 68 major mode")
+
+;;;###autoload
+(add-to-list 'auto-mode-alist '("\\.a68\\'" . a68-mode))
+
+(defconst a68-font-lock-keywords
+ (list
+ (cons (concat "\\<\\("
+ "DECS\\|PROGRAM\\|CONTEXT\\|USE\\|FINISH\\|KEEP"
+ "\\|ALIEN"
+ "\\|MODE\\|OP\\|PRIO\\|PROC"
+ "\\|PROC"
+ "\\|OF\\|AT\\|IS\\|ISNT\\|EMPTY\\|SKIP"
+ "\\|PR\\|PRAGMAT"
+ "\\|CASE\\|IN\\|OUSE\\|OUT\\|ESAC\\|"
+ "\\|FOR\\|FORALL\\|FROM\\|TO\\|BY\\|WHILE\\|DO\\|OD"
+ "\\|IF\\|THEN\\|ELIF\\|THEN\\|ELSE\\|FI"
+ "\\|PAR\\|BEGIN\\|END\\|GOTO\\|EXIT"
+ "\\|LWB\\|UPB\\|NOT\\|ABS\\|BIN\\|REPR\\|LENG\\|SHORTEN\\|ODD\\|SIGN\\|ROUND\\ENTIER"
+ "\\|AND\\|OR\\|DIV\\|OVER\\|MOD\\|ELEM\\|SHL\\|SHR\\|IS\\|ISNT"
+ "\\|OVERAB\\|DIVAB\\|MODAB"
+ "\\|REF"
+ "\\)\\>")
+ 'font-lock-keyword-face)
+ (cons (concat "\\<\\("
+ "TRUE\\|\\FALSE"
+ "\\)\\>")
+ 'font-lock-constant-face)
+ ;; Note that the following rule is only valid for bold stropping.
+ (cons (concat "\\<[A-Z]+\\>") 'font-lock-type-face)
+
+ (cons "\\('\\w*'\\)"
+ font-lock-variable-name-face))
+ "Highlighting expressions for Algol 68 mode")
+
+(defun a68-within-string ()
+ (nth 3 (syntax-ppss)))
+
+(defun a68-within-comment ()
+ (nth 4 (syntax-ppss)))
+
+;; Indentation rules:
+;;
+;; - If we are at the beginning of the buffer, or looking at some
+;; indent-0 content, indent to column 0.
+;;
+;; - If we are currently at an END, ), FI or OD, then de-indent
+;; relative to the previous line.
+;;
+;; - If we first see and "end line" before our current line,
+;; then we should indent our current line to the same indentation as
+;; the end line.
+;;
+;; - If we first see a "start line" like IF, then we need to increase
+;; our indentation relative to that start line.
+;;
+;; - If into a balanced expression, we should indent to the column
+;; where the start of the innermost parenthetical group.
+;;
+;; - If none of the above apply, then do not indent at all.
+
+(defun a68-indent-line ()
+ "Indent current line as Algol 68 code"
+ (interactive)
+ (let ((case-fold-search nil))
+ (save-excursion
+ (beginning-of-line)
+ (if (nth 1 (syntax-ppss)) ; Check for rule 5
+ (let ((offset (save-excursion (goto-char (+ (nth 1 (syntax-ppss)) 1))
+ (current-column))))
+ (indent-line-to offset))
+ (if (or (bobp) ; Check for rule 1
+ (looking-at "^[ \t]*\\<\\(KEEP\\|FINISH\\|DECS\\|USE\\|PROGRAM\\)\\>"))
+ (indent-line-to 0)
+ (let ((not-indented t)
+ (prev-indent (current-indentation))
+ (begin-indent-re "^[ \t]*\\<\\(PAR\\|BEGIN\\|KEEP\\|IF\\|DO\\|ELSE\\|ELIF\\|THEN\\)")
+ (deindent-line-re "^[ \t]*\\<\\(END\\|FI\\|OD\\|ELSE\\|ELIF\\)\\>")
+ (eqindent-line-re "^[ \t]*\\<\\(THEN\\)\\>")
+ (end-line-re "^[ \t]*\\(END\\|FI\\|OD\\)")
+ cur-indent)
+ (if (looking-at eqindent-line-re)
+ (save-excursion
+ (forward-line -1)
+ (setq cur-indent (current-indentation)))
+ (if (looking-at deindent-line-re) ; Check for rule 2
+ (progn
+ (save-excursion
+ (forward-line -1)
+ (setq cur-indent (- (current-indentation) a68-indent-step)))
+ (if (< cur-indent 0)
+ (setq cur-indent 0)))
+ (save-excursion
+ (while not-indented
+ (forward-line -1)
+ (if (looking-at end-line-re) ; Check for rule 3
+ (progn
+ (setq cur-indent (current-indentation))
+ (setq not-indented nil))
+ ;; Check for rule 4
+ (if (looking-at begin-indent-re)
+ (progn
+ (setq cur-indent (+ (current-indentation) a68-indent-step))
+ (setq not-indented nil))
+ (if (bobp) ; Check for rule 5
+ (setq not-indented nil))))))))
+ (if cur-indent
+ (indent-line-to cur-indent)
+ ;; If we didn't see an indentation hint, then allow no
+ ;; indentation.
+ (indent-line-to 0)))))))
+ (when (< (current-column) (current-indentation))
+ (move-to-column (current-indentation))))
+
+(defvar a68-mode-syntax-table
+ (let ((st (make-syntax-table)))
+ (modify-syntax-entry ?{ "<" st)
+ (modify-syntax-entry ?# "<" st)
+ (modify-syntax-entry ?} ">" st)
+ (modify-syntax-entry ?# ">" st)
+ (modify-syntax-entry ?\\ "." st)
+;; (modify-syntax-entry ?C "< 13" st)
+;; (modify-syntax-entry ?O "> 24" st)
+ ;; define parentheses to match
+ (modify-syntax-entry ?\( "()" st)
+ (modify-syntax-entry ?\) ")(" st)
+ st))
+
+;;;
+;;; Electric functions
+;;;
+
+(defconst a68-autoindent-lines-re
+ "\\<\\(BEGIN\\|END\\|ELSE\\|ELIF\\|DO\\|OD\\|CASE\\|ESAC\\|IN\\|OUT\\)\\>")
+
+(defun electric-a68-terminate-line ()
+ "Terminate line and indent next line."
+ (interactive)
+ ;; First, check if current line should be indented
+ (save-excursion
+ (beginning-of-line)
+ (skip-chars-forward " \t")
+ (if (looking-at a68-autoindent-lines-re)
+ (a68-indent-line)))
+ (delete-horizontal-space) ; Removes triling whitespaces
+ ;; Indent next line if we are not in a string
+ (let ((in-string (a68-within-string)))
+ (newline)
+ (unless in-string
+ (a68-indent-line))))
+
+(defun electric-a68-tab ()
+ "Function called when TAB is pressed in Algol68 mode."
+ (interactive)
+ (unless (save-excursion
+ (beginning-of-line)
+ (a68-within-string))
+ (a68-indent-line)))
+
+(defun algol-mode ()
+ "Major mode for editing Algol 68 files."
+ (interactive)
+ (kill-all-local-variables)
+ (set-syntax-table a68-mode-syntax-table)
+ (use-local-map a68-mode-map)
+ (set (make-local-variable 'font-lock-defaults)
+ '(a68-font-lock-keywords))
+ (set (make-local-variable 'indent-line-function)
+ 'a68-indent-line)
+ (setq major-mode 'a68-mode)
+ (setq mode-name "Algol68")
+ (run-hooks 'a68-mode-hooks))
+
+(provide 'algol-mode)
