Define multi-character parentheses in Emacs

Question

In Verilog you enclose code blocks between the words 'begin' and 'end' like this:

if(foo) begin
   x <= 1'b0;
   y <= 1'b0;
end else begin
   x <= x_d;
   y <= y_d;
end

Is there any way to set begin and end as parentheses in Emacs, so that you can use check-parens or similar to find any that are mismatched?

I've tried adding this (and variations of) to my ~/.emacs file, but it doesn't like it...

(modify-syntax-entry ?begin "(end" )
(modify-syntax-entry ?end ")begin" )

Thanks.

Things like this is typically handled by the indentation engine. You could use it to check syntax, for example by marking the entire buffer and run `indent-region`. If the end of the file is incorrectly indented, you have a begin/end mismatch. — Lindydancer, May 17 '12 at 09:53
@Lindydancer thanks, but I'm working on code that is being edited by several people at once, all using different editors, and so often different sections of the code are indented in different ways. Also some of the files tend to be very long, and the select all `indent-region` can take a long time... — Katy Montgomerie, May 17 '12 at 11:22
In that case, I would simple write a custom package finding matching begin/end pairs. It's not trivial, but I think it would be a good exercise in elisp, if you are new to it. — Lindydancer, May 17 '12 at 12:07

score 3 · Accepted Answer · answered May 18 '12 at 19:22

Sadly, Emacs's parenthesis matching infrastructure doesn't understand much of multi-character tokens. The new library SMIE added in Emacs-23.4 is partly intended to address this issue. It lets major modes describe the syntax of the language (in a very limited kind of grammar) after which things like C-M-f and C-M-b will know how to jump over logical elements, e.g. skip from a begin to its matching end. As LindyDancer notes, such things are usually needed for indentation, and indeed the main motivation behind SMIE was to provide a generic indentation engine.

Now Verilog doesn't use SMIE but it does implement similar navigation commands. So you could probably try something like

(defun sm-verilog-check-parens ()
  (save-excursion
    (goto-char (point-min))
    (while (not (eobp))
      (verilog-forward-sexp))))

Tho I do not know if verilog-forward-sexp will give you appropriate warnings/errors if it bumps into the end of buffer at an unexpected moment.

Define multi-character parentheses in Emacs

1 Answers1