Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Sun, 24 Aug 2014 21:42:44 +0200

Am Montag, 18. August 2014, 10:46:57 schrieb Michael Davidsaver:
> One of changes I'm considering (after the linking/locking work) is to
> re-write the DBD file parser.
> 
> The idea would be to parse into an intermediate structure which would be
> more general than dbStatic.  This would define points in the syntax for
> future expansion, and avoid some of the chicken and egg problems of the
> present code.

This reminds me of the following idea I had some years ago, which might be 
similar or not to what you have in mind.

The db/dbd syntax can be generalized to a very simple syntax that basically 
recognizes one kind of item:

  item ::= keyword "(" arg "," ... ")" [ "{" item ... "}" ]

(where 'arg' is defined by the lexical syntax as a quoted or unquoted string, 
and 'keyword' is a sequence of lower case letters). A lookup-table defines the 
mapping of keywords to functions of type

  void parse_item(database *db, arg_list *args, item_list *items);

This function then checks that the number and types of its arguments and sub-
items are correct, produces the final output and adds it to the database.

I am fully aware that there are many details missing in this picture, this is 
merely a rough sketch of the idea, not a full design spec.

The main point is that the syntax is now easily extensible by adding a new 
keyword and the corresponding function in the table. Unknown keywords 
(together with the item they introduce) are ignored (or optionally give 
warning), so that future extensions never break existing parsers.

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System