Re: syntax table entries for comments

[Stefan Monnier]

> 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.

Emacs does not properly support this, as you've discovered.

> (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))

Could you tell me the place from which this code was inspired so we can
fix it ?  It should look like:

   (defvar nrx-mode-syntax-table
     (let ((st (make-syntax-table)))
       (modify-syntax-entry ...)
       (modify-syntax-entry ...)
       ...
       st))

and the `set-syntax-table' is commonly done implicitly by
`define-derived-mode'.

> 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?

Nothing, really, other than the fact that it's a limitation of current
syntax-tables.  You can either hack on src/syntax.c to add support for
such cases, or use font-lock-syntactic-keywords to recognize `--'
and mark it as a comment starter.


        Stefan