On Sunday 02 May 2004 05:05, Olivier Biot wrote:
> Hi list,
>
> I'd appreciate if someone could give me some insights on the display
> filter engine I currently don't have. The reason for this is that I
> plan to work on some extra display filter operations, but I don't know
> for now where to do what :)
>
> There is a grammar.lemon file and a scanner.l file. Could someone tell
> me what is in what, and which gets used when in parsing a display
> filter?
>
scanner.l looks at the display filter string and finds reserved words,
punctuation, etc. This information gets passed to the parser produced by
grammar.lemon. The grammar's job is to create a syntax-tree out of the
information provided by the scanner. The syntax tree organizes the
information from the scanner into something that is grammatical in the
dfilter language.
The routines in semcheck.c then check the semantics of the syntax tree, and do
any modifications necessary to the syntax tree to make the dfilter work....
things like converting val_strings to integers, etc.
Then gencode.c converts the syntax tree into a list of "dfvm" (display filter
virtual machine) instructions. These dfvm instructions are what runs the
display filter engine.
(I'll think about the rest of your questions a bit later, when I have some
more time)
--gilbert
