syntax table entries for comments

[Arjan Bos]

Hi all,

First of, many thanks to those who answered my question about info for 
major-mode writers. The mode tutorial on emacs wiki was most 
enlightning. In fact it was so helpful, that I decided to completely 
rewrite the major-mode for NetRexx. When it's done I'll post it in 
gnu.emacs.sources.

But before that can happen, I'll need some clues. NetRexx is a 
programming language that contains two types of comments. The first is 
for large blocks and is the familiar /* */ construction. This I can do 
by looking at the examples. The second one is a single-line comment that 
consists of two hyphens, like:
  -- this is a comment.

Based on the major mode tutorial I did put the following code in:

(defvar nrx-mode-syntax-table nil
  "Syntax table in use in NRX-mode buffers.")

(defun nrx-create-syntax-table ()
  (if nrx-mode-syntax-table
      ()
    (setq nrx-mode-syntax-table (make-syntax-table))
    (modify-syntax-entry ?. "." nrx-mode-syntax-table)
    (modify-syntax-entry ?- ". 12b" nrx-mode-syntax-table)
    (modify-syntax-entry ?/ ". 14" nrx-mode-syntax-table)
    (modify-syntax-entry ?* ". 23" nrx-mode-syntax-table)
    (modify-syntax-entry ?\n "> b" nrx-mode-syntax-table)
    (modify-syntax-entry ?\' "\"" nrx-mode-syntax-table))

  (set-syntax-table nrx-mode-syntax-table))

This works but also renders the combination -* and *- as comment start 
and end, which is wrong. Could anyone please tell me what I'm missing?

TIA,

Arjan