bnfc.el

;;; bnfc.el --- Define context-free grammars for the BNFC tool

;; Copyright (C) 2016  Jacob Mitchell <jmitchell@member.fsf.org>

;; Author: Jacob Mitchell <jmitchell@member.fsf.org>
;; URL: https://github.com/jmitchell/bnfc-mode
;; Keywords: languages, tools
;; Version: 0.4
;; Package-Requires: ((emacs "24.3"))

;; This file is not part of GNU Emacs.

;; This file 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.

;; This file 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 file. If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; bnfc-mode simplifies editing BNFC input files in Emacs.  BNFC is a
;; handy tool for converting context-free grammars into parsers,
;; syntax highlighters, and documentation.

;;; Code:

;;;###autoload
(add-to-list 'auto-mode-alist '("\\.cf\\'" . bnfc-mode))

(defconst bnfc-mode-syntax-table
  (let ((table (make-syntax-table)))
    (modify-syntax-entry ?\" "\"" table)
    (modify-syntax-entry ?\{ "(}1c" table)
    (modify-syntax-entry ?\} "){4c" table)
    (modify-syntax-entry ?- "_ 123" table)
    (modify-syntax-entry ?\n ">" table)
    table))

(defconst bnfc-keywords
  '("char"
    "coercions"
    "comment"
    "digit"
    "entrypoints"
    "eps"
    "internal"
    "layout"
    "letter"
    "lower"
    "nonempty"
    "position"
    "rules"
    "separator"
    "stop"
    "terminator"
    "token"
    "toplevel"
    "upper"))

(defconst bnfc-builtins
  '("Char"
    "Double"
    "Ident"
    "Integer"
    "String"))

(defconst bnfc-label
  (rx symbol-start
      (group upper (0+ (any letter digit "_")))
      symbol-end
      (0+ space)
      "."))

(defconst bnfc-production-variable
  ;; Regexp overlaps with BNFC-LABEL, but ordering of the
  ;; FONT-LOCK-DEFAULTS resolves the ambiguity. Strings matching both
  ;; regexps are treated as labels.
  (rx symbol-start
      (group upper (0+ (any letter digit "_")))
      symbol-end))

(defvar bnfc-font-lock-keywords
  (append
   `((,(regexp-opt bnfc-keywords 'symbols) . font-lock-keyword-face)
     (,(regexp-opt bnfc-builtins 'symbols) . font-lock-builtin-face)
     (,bnfc-label 1 font-lock-variable-name-face)
     (,bnfc-production-variable 1 font-lock-type-face))))

;;;###autoload
(define-derived-mode bnfc-mode prog-mode "BNFC"
  :syntax-table bnfc-mode-syntax-table
  (setq-local font-lock-defaults '(bnfc-font-lock-keywords))
  (setq-local comment-start "--")
  (setq-local comment-end ""))

(provide 'bnfc)
;;; bnfc.el ends here