diff --git a/sex-mode.el b/sex-mode.el
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+++ b/sex-mode.el
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+(require 'lisp-mode)
+
+(defgroup sex-mode nil
+  "Major mode for Sex code."
+  :prefix 'sex-
+  :group 'languages)
+
+(define-abbrev-table 'sex-mode-abbrev-table ()
+  "Abbrev table for Sex mode.
+It has `lisp-mode-abbrev-table' as its parent."
+  :parents (list lisp-mode-abbrev-table))
+
+(defvar sex-mode-syntax-table
+  (let ((table (make-syntax-table lisp-data-mode-syntax-table)))
+    table))
+
+(defvar sex-mode-map
+  (let ((map (make-sparse-keymap)))
+    (set-keymap-parent map lisp-mode-shared-map)
+    map)
+  "Keymap for Sex mode.
+All commands in `lisp-mode-shared-map' are inherited by this map.")
+
+(defvar sex-mode-line-process "")
+
+(defconst sex-font-lock-keywords
+  (eval-when-compile
+    (list
+     ;; Declarations
+     (list (concat "("
+                   (regexp-opt '("include"
+                                 "fn"
+                                 "struct"
+                                 "template"
+                                 "var")
+                               'word)
+                   "\\>"
+                   "[[:space:]]*"
+                   "\\([[:word:]]*\\)")
+           '(1 font-lock-keyword-face)
+           '(2 font-lock-function-name-face))
+     ;; Keywords
+     (list (concat "("
+                   (regexp-opt '(
+                                 "case"
+                                 "do"
+                                 "if"
+                                 "for"
+                                 "goto"
+                                 "return"
+                                 "switch"
+                                 "var"
+                                 "while")
+                               'word)
+                   "\\>")
+           '(1 'font-lock-builtin-face)))))
+
+(defun sex-mode-set-variables ()
+  (set-syntax-table sex-mode-syntax-table)
+  (setq local-abbrev-table sex-mode-abbrev-table)
+  (setq mode-line-process '("" sex-mode-line-process))
+  (setq font-lock-defaults
+        '((sex-font-lock-keywords)
+          nil nil
+          (("+-*/.<>=!?$%_&:" . "w"))
+          nil
+          (font-lock-mark-block-function . mark-defun)))
+  (setq-local prettify-symbols-alist lisp-prettify-symbols-alist))
+
+(put 'fn 'lisp-indent-function 'defun)
+(put 'template 'lisp-indent-function 'defun)
+(put 'struct 'lisp-indent-function 'defun)
+(put 'var 'lisp-indent-function 0)
+
+;;;###autoload
+(define-derived-mode sex-mode lisp-data-mode "Sex"
+  "Major mode for editing Sex code.
+Editing commands are similar to those of `lisp-mode'.
+
+Commands:
+Delete converts tabs to spaces as it moves back.
+Blank lines separate paragraphs.  Semicolons start comments.
+\\{sex-mode-map}"
+  :group 'sex-mode
+  (sex-mode-set-variables))
+
+;;;###autoload
+(add-to-list 'auto-mode-alist '("\\.\\(sex\\|hsex\\)\\'" . sex-mode))
+
+(provide 'sex-mode)