1 ;;; a68-mode.el --- Major mode for editing Algol 68 code
2 
3 ;; Copyright (C) 2011 Jose E. Marchesi
4 
5 ;; Maintainer: Jose E. Marchesi
6 
7 ;; This file is NOT part of GNU Emacs.
8 
9 ;; This program is free software; you can redistribute it and/or modify
10 ;; it under the terms of the GNU General Public License as published by
11 ;; the Free Software Foundation; either version 3, or (at your option)
12 ;; any later version.
13 
14 ;; This program is distributed in the hope that it will be useful,
15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
17 ;; GNU General Public License for more details.
18 
19 ;; You should have received a copy of the GNU General Public License
20 ;; along with this program; see the file COPYING.  If not, write to the
21 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
22 ;; Boston, MA 02110-1301, USA.
23 
24 ;;; Commentary:
25 
26 ;; A major mode for editing Algol 68 code.
27 ;;
28 ;; TODO: support quote and dot stropping.
29 
30 ;;; Code:
31 
32 (require 'syntax)
33 (require 'font-lock)
34 
35 (defvar a68-indent-step 3
36   "Indentation step for Algol 68.")
37 
38 (defvar a68-mode-hook nil)
39 
40 (defvar a68-mode-map
41   (let ((map (make-keymap)))
42     (define-key map "\C-j" 'newline-and-indent)
43     (define-key map "\r"   'electric-a68-terminate-line)
44     (define-key map "\t"   'electric-a68-tab)
45     map)
46   "Keymap for Algol 68 major mode.")
47 
48 ;;;###autoload
49 (add-to-list 'auto-mode-alist '("\\.a68\\'" . a68-mode))
50 
51 (defconst a68-font-lock-keywords
52   (list
53    (cons (concat "\\<\\("
54                  "DECS\\|PROGRAM\\|CONTEXT\\|USE\\|FINISH\\|KEEP"
55                  "\\|ALIEN"
56                  "\\|MODE\\|OP\\|PRIO\\|PROC"
57                  "\\|PROC"
58                  "\\|OF\\|AT\\|IS\\|ISNT\\|EMPTY\\|SKIP"
59                  "\\|PR\\|PRAGMAT"
60                  "\\|CASE\\|IN\\|OUSE\\|OUT\\|ESAC\\|"
61                  "\\|FOR\\|FORALL\\|FROM\\|TO\\|BY\\|WHILE\\|DO\\|OD"
62                  "\\|IF\\|THEN\\|ELIF\\|THEN\\|ELSE\\|FI"
63                  "\\|PAR\\|BEGIN\\|END\\|GOTO\\|EXIT"
64                  "\\|LWB\\|UPB\\|NOT\\|ABS\\|BIN\\|REPR\\|LENG\\|SHORTEN\\|ODD\\|SIGN\\|ROUND\\ENTIER"
65                  "\\|AND\\|OR\\|DIV\\|OVER\\|MOD\\|ELEM\\|SHL\\|SHR\\|IS\\|ISNT"
66                  "\\|OVERAB\\|DIVAB\\|MODAB"
67                  "\\|REF"
68                  "\\)\\>")
69          'font-lock-keyword-face)
70    (cons (concat "\\<\\("
71                  "TRUE\\|\\FALSE"
72                  "\\)\\>")
73          'font-lock-constant-face)
74    ;; Note that the following rule is only valid for bold stropping.
75    (cons (concat "\\<[A-Z]+\\>") 'font-lock-type-face)
76 
77    (cons "\\('\\w*'\\)"
78          font-lock-variable-name-face))
79   "Highlighting expressions for Algol 68 mode.")
80 
81 (defun a68-within-string ()
82   "Check if inside a string."
83   (nth 3 (syntax-ppss)))
84 
85 (defun a68-within-comment ()
86   "Check if inside a comment."
87   (nth 4 (syntax-ppss)))
88 
89 ;; Indentation rules:
90 ;;
91 ;; - If we are at the beginning of the buffer, or looking at some
92 ;;   indent-0 content, indent to column 0.
93 ;;
94 ;; - If we are currently at an END, ), FI or OD, then de-indent
95 ;;   relative to the previous line.
96 ;;
97 ;; - If we first see and "end line" before our current line,
98 ;;   then we should indent our current line to the same indentation as
99 ;;   the end line.
100 ;;
101 ;; - If we first see a "start line" like IF, then we need to increase
102 ;;   our indentation relative to that start line.
103 ;;
104 ;; - If into a balanced expression, we should indent to the column
105 ;;   where the start of the innermost parenthetical group.
106 ;;
107 ;; - If none of the above apply, then do not indent at all.
108 
109 (defun a68-indent-line ()
110   "Indent current line as Algol 68 code."
111   (interactive)
112   (let ((case-fold-search nil))
113     (save-excursion
114       (beginning-of-line)
115       (if (nth 1 (syntax-ppss)) ; Check for rule 5
116           (let ((offset (save-excursion (goto-char (+ (nth 1 (syntax-ppss)) 1))
117                                         (current-column))))
118             (indent-line-to offset))
119         (if (or (bobp) ; Check for rule 1
120                 (looking-at "^[ \t]*\\<\\(KEEP\\|FINISH\\|DECS\\|USE\\|PROGRAM\\)\\>"))
121             (indent-line-to 0)
122           (let ((not-indented t)
123                 (prev-indent (current-indentation))
124                 (begin-indent-re "^[ \t]*\\<\\(PAR\\|BEGIN\\|KEEP\\|IF\\|DO\\|ELSE\\|ELIF\\|THEN\\)")
125                 (deindent-line-re "^[ \t]*\\<\\(END\\|FI\\|OD\\|ELSE\\|ELIF\\)\\>")
126                 (eqindent-line-re "^[ \t]*\\<\\(THEN\\)\\>")
127                 (end-line-re "^[ \t]*\\(END\\|FI\\|OD\\)")
128                 cur-indent)
129             (if (looking-at eqindent-line-re)
130                 (save-excursion
131                   (forward-line -1)
132                   (setq cur-indent (current-indentation)))
133               (if (looking-at deindent-line-re) ; Check for rule 2
134                   (progn
135                     (save-excursion
136                       (forward-line -1)
137                       (setq cur-indent (- (current-indentation) a68-indent-step)))
138                     (if (< cur-indent 0)
139                         (setq cur-indent 0)))
140                 (save-excursion
141                   (while not-indented
142                     (forward-line -1)
143                     (if (looking-at end-line-re) ; Check for rule 3
144                         (progn
145                           (setq cur-indent (current-indentation))
146                           (setq not-indented nil))
147                       ;; Check for rule 4
148                       (if (looking-at begin-indent-re)
149                           (progn
150                             (setq cur-indent (+ (current-indentation) a68-indent-step))
151                             (setq not-indented nil))
152                         (if (bobp) ; Check for rule 5
153                             (setq not-indented nil))))))))
154             (if cur-indent
155                 (indent-line-to cur-indent)
156               ;; If we didn't see an indentation hint, then allow no
157               ;; indentation.
158               (indent-line-to 0)))))))
159   (when (< (current-column) (current-indentation))
160     (move-to-column (current-indentation))))
161 
162 (defvar a68-mode-syntax-table
163   (let ((st (make-syntax-table)))
164     (modify-syntax-entry ?{ "<" st)
165     (modify-syntax-entry ?# "<" st)
166     (modify-syntax-entry ?} ">" st)
167     (modify-syntax-entry ?# ">" st)
168     (modify-syntax-entry ?\\ "." st)
169 ;;    (modify-syntax-entry ?C "< 13" st)
170 ;;    (modify-syntax-entry ?O "> 24" st)
171     ;; define parentheses to match
172     (modify-syntax-entry ?\( "()" st)
173     (modify-syntax-entry ?\) ")(" st)
174     st))
175 
176 ;;;
177 ;;; Electric functions
178 ;;;
179 
180 (defconst a68-autoindent-lines-re
181   "\\<\\(BEGIN\\|END\\|ELSE\\|ELIF\\|DO\\|OD\\|CASE\\|ESAC\\|IN\\|OUT\\)\\>")
182 
183 (defun electric-a68-terminate-line ()
184   "Terminate line and indent next line."
185   (interactive)
186   ;; First, check if current line should be indented
187   (save-excursion
188     (beginning-of-line)
189     (skip-chars-forward " \t")
190     (if (looking-at a68-autoindent-lines-re)
191         (a68-indent-line)))
192   (delete-horizontal-space) ; Removes triling whitespaces
193   ;; Indent next line if we are not in a string
194   (let ((in-string (a68-within-string)))
195     (newline)
196     (unless in-string
197       (a68-indent-line))))
198 
199 (defun electric-a68-tab ()
200   "Function called when TAB is pressed in Algol68 mode."
201   (interactive)
202   (unless (save-excursion
203             (beginning-of-line)
204             (a68-within-string))
205     (a68-indent-line)))
206 
207 ;;;###autoload
208 (define-derived-mode a68-mode prog-mode "Algol68"
209   "Major mode for editing Alogl68 files."
210   (setq-local font-lock-defaults '(a68-font-lock-keywords))
211   (setq-local indent-line-function #'a68-indent-line)
212   (setq-local comment-start "#")
213   (setq-local comment-end "#"))
214 
215 ;;;###autoload
216 (add-to-list 'auto-mode-alist '("\\.a68\\'" . a68-mode))
217 
218 (provide 'algol-mode)
219 ;;; algol-mode.el ends here