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 '()
39   "Hook run when entering Algol68 mode.")
40 
41 (defvar a68-mode-map
42   (let ((map (make-keymap)))
43     (define-key map "\C-j" #'newline-and-indent)
44     (define-key map "\r"   #'a68-electric-terminate-line)
45     (define-key map "\t"   #'a68-electric-tab)
46     map)
47   "Keymap for Algol 68 major mode.")
48 
49 (defconst a68-font-lock-keywords
50   (list
51    (cons (concat "\\<\\("
52                  "DECS\\|PROGRAM\\|CONTEXT\\|USE\\|FINISH\\|KEEP"
53                  "\\|ALIEN"
54                  "\\|MODE\\|OP\\|PRIO\\|PROC"
55                  "\\|PROC"
56                  "\\|OF\\|AT\\|IS\\|ISNT\\|EMPTY\\|SKIP"
57                  "\\|PR\\|PRAGMAT"
58                  "\\|CASE\\|IN\\|OUSE\\|OUT\\|ESAC\\|"
59                  "\\|FOR\\|FORALL\\|FROM\\|TO\\|BY\\|WHILE\\|DO\\|OD"
60                  "\\|IF\\|THEN\\|ELIF\\|THEN\\|ELSE\\|FI"
61                  "\\|PAR\\|BEGIN\\|END\\|GOTO\\|EXIT"
62                  "\\|LWB\\|UPB\\|NOT\\|ABS\\|BIN\\|REPR\\|LENG\\|SHORTEN\\|ODD\\|SIGN\\|ROUND\\ENTIER"
63                  "\\|AND\\|OR\\|DIV\\|OVER\\|MOD\\|ELEM\\|SHL\\|SHR\\|IS\\|ISNT"
64                  "\\|OVERAB\\|DIVAB\\|MODAB"
65                  "\\|REF"
66                  "\\)\\>")
67          'font-lock-keyword-face)
68    (cons (concat "\\<\\("
69                  "TRUE\\|\\FALSE"
70                  "\\)\\>")
71          'font-lock-constant-face)
72    ;; Note that the following rule is only valid for bold stropping.
73    (cons (concat "\\<[A-Z]+\\>") 'font-lock-type-face)
74 
75    (cons "\\('\\w*'\\)"
76          font-lock-variable-name-face))
77   "Highlighting expressions for Algol 68 mode.")
78 
79 (defun a68-within-string ()
80   "Check if inside a string."
81   (nth 3 (syntax-ppss)))
82 
83 (defun a68-within-comment ()
84   "Check if inside a comment."
85   (nth 4 (syntax-ppss)))
86 
87 ;; Indentation rules:
88 ;;
89 ;; - If we are at the beginning of the buffer, or looking at some
90 ;;   indent-0 content, indent to column 0.
91 ;;
92 ;; - If we are currently at an END, ), FI or OD, then de-indent
93 ;;   relative to the previous line.
94 ;;
95 ;; - If we first see and "end line" before our current line,
96 ;;   then we should indent our current line to the same indentation as
97 ;;   the end line.
98 ;;
99 ;; - If we first see a "start line" like IF, then we need to increase
100 ;;   our indentation relative to that start line.
101 ;;
102 ;; - If into a balanced expression, we should indent to the column
103 ;;   where the start of the innermost parenthetical group.
104 ;;
105 ;; - If none of the above apply, then do not indent at all.
106 
107 (defun a68-indent-line ()
108   "Indent current line as Algol 68 code."
109   (interactive)
110   (let ((case-fold-search nil))
111     (save-excursion
112       (beginning-of-line)
113       (if (nth 1 (syntax-ppss)) ; Check for rule 5
114           (let ((offset (save-excursion (goto-char (+ (nth 1 (syntax-ppss)) 1))
115                                         (current-column))))
116             (indent-line-to offset))
117         (if (or (bobp) ; Check for rule 1
118                 (looking-at "^[ \t]*\\<\\(KEEP\\|FINISH\\|DECS\\|USE\\|PROGRAM\\)\\>"))
119             (indent-line-to 0)
120           (let ((not-indented t)
121                 (prev-indent (current-indentation))
122                 (begin-indent-re "^[ \t]*\\<\\(PAR\\|BEGIN\\|KEEP\\|IF\\|DO\\|ELSE\\|ELIF\\|THEN\\)")
123                 (deindent-line-re "^[ \t]*\\<\\(END\\|FI\\|OD\\|ELSE\\|ELIF\\)\\>")
124                 (eqindent-line-re "^[ \t]*\\<\\(THEN\\)\\>")
125                 (end-line-re "^[ \t]*\\(END\\|FI\\|OD\\)")
126                 cur-indent)
127             (if (looking-at eqindent-line-re)
128                 (save-excursion
129                   (forward-line -1)
130                   (setq cur-indent (current-indentation)))
131               (if (looking-at deindent-line-re) ; Check for rule 2
132                   (progn
133                     (save-excursion
134                       (forward-line -1)
135                       (setq cur-indent (- (current-indentation) a68-indent-step)))
136                     (if (< cur-indent 0)
137                         (setq cur-indent 0)))
138                 (save-excursion
139                   (while not-indented
140                     (forward-line -1)
141                     (if (looking-at end-line-re) ; Check for rule 3
142                         (progn
143                           (setq cur-indent (current-indentation))
144                           (setq not-indented nil))
145                       ;; Check for rule 4
146                       (if (looking-at begin-indent-re)
147                           (progn
148                             (setq cur-indent (+ (current-indentation) a68-indent-step))
149                             (setq not-indented nil))
150                         (if (bobp) ; Check for rule 5
151                             (setq not-indented nil))))))))
152             (if cur-indent
153                 (indent-line-to cur-indent)
154               ;; If we didn't see an indentation hint, then allow no
155               ;; indentation.
156               (indent-line-to 0)))))))
157   (when (< (current-column) (current-indentation))
158     (move-to-column (current-indentation))))
159 
160 (defvar a68-mode-syntax-table
161   (let ((st (make-syntax-table)))
162     (modify-syntax-entry ?{ "<" st)
163     (modify-syntax-entry ?# "<" st)
164     (modify-syntax-entry ?} ">" st)
165     (modify-syntax-entry ?# ">" st)
166     (modify-syntax-entry ?\\ "." st)
167 ;;    (modify-syntax-entry ?C "< 13" st)
168 ;;    (modify-syntax-entry ?O "> 24" st)
169     ;; define parentheses to match
170     (modify-syntax-entry ?\( "()" st)
171     (modify-syntax-entry ?\) ")(" st)
172     st))
173 
174 ;;;
175 ;;; Electric functions
176 ;;;
177 
178 (defconst a68-autoindent-lines-re
179   "\\<\\(BEGIN\\|END\\|ELSE\\|ELIF\\|DO\\|OD\\|CASE\\|ESAC\\|IN\\|OUT\\)\\>")
180 
181 (defun a68-electric-terminate-line ()
182   "Terminate line and indent next line."
183   (interactive)
184   ;; First, check if current line should be indented
185   (save-excursion
186     (beginning-of-line)
187     (skip-chars-forward " \t")
188     (if (looking-at a68-autoindent-lines-re)
189         (a68-indent-line)))
190   (delete-horizontal-space) ; Removes triling whitespaces
191   ;; Indent next line if we are not in a string
192   (let ((in-string (a68-within-string)))
193     (newline)
194     (unless in-string
195       (a68-indent-line))))
196 
197 (defun a68-electric-tab ()
198   "Function called when TAB is pressed in Algol68 mode."
199   (interactive)
200   (unless (save-excursion
201             (beginning-of-line)
202             (a68-within-string))
203     (a68-indent-line)))
204 
205 ;;;###autoload
206 (define-derived-mode a68-mode prog-mode "Algol68"
207   "Major mode for editing Alogl68 files."
208   (setq-local font-lock-defaults '(a68-font-lock-keywords))
209   (setq-local indent-line-function #'a68-indent-line)
210   (setq-local comment-start "#")
211   (setq-local comment-end "#"))
212 
213 ;;;###autoload
214 (add-to-list 'auto-mode-alist '("\\.a68\\'" . a68-mode))
215 
216 (provide 'algol-mode)
217 ;;; algol-mode.el ends here