[alsa-devel] [PATCH] ascenario: Add scenario support to alsa-lib

[Jaroslav Kysela]

On Wed, 7 Oct 2009, Takashi Iwai wrote:

>> But regarding goto, I'm really stuck. We can add some block control:
>>
>> BEGIN="" .. END="" (looks like a goto anyway)
>
> Hm, still not much improvement, indeed.
>
>> Or skip some lines:
>>
>> SKIPLINES="3"
>
> Oh, no!  I don't want to debug a DSP assembly :)
>
>> But these solutions do not bring much readability. Another possibility
>> (compromise) is to use a goto command to skip all lines to next label to
>> reduce usage of named labels (which is not a big fun at least in
>> init/default file):
>>
>> GOTO=""
>> ....
>> LABEL=""
>>
>> It works without any code change in current parser.
>
> I'm afraid that udev config is way too simple for the conditionals.

There are plenty conditionals in udev configuration files. That was main 
reason to use this syntax for alsactl.

> And we do need conditionals to handle many cases.  XML can do better
> for such a purpose, but moving to XML now is another question...

Really better? XML is good for static data but not for non-linear 
execution. Take look to HTML/Javascript. Javascript is doing the 
non-linear stuff and eventually modifies XML at runtime. We have similar 
situation in alsa-lib. The syntax structure is changed at runtime 
depending on external data. But it requires some system resources 
(memory).

Things why I chose udev-like syntax:

- well known "key operator value" syntax
- very easy to parse
- parser reads and executes code directly without storing the source
   or portions to memory (really small memory usage)
- normal conditions are really small in syntax files

If only the goto command is major drawback, I can live with it.

We need to take account the useability and the implementation complexity. 
I think a compromise is essential.

 						Jaroslav

-----
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.