Re: Substitutions defaults and tricks

[Andrew Johnson <anj@aps.anl.gov>]

Hi Garth,

There have been some significant modifications made to the version of 
msi which is found in Base 3.15. I'm not sure if they will completely 
solve your problem, but you might want to check the documentation at 
http://www.aps.anl.gov/epics/base/R3-15/0-docs/msi.html which shows the 
new global syntax in the substitutions file. There are more docs 
including an EBNF grammar in the Application Developers Guide at 
http://www.aps.anl.gov/epics/base/R3-15/0-docs/AppDevGuide/node7.html#SECTION007220000000000000000 
-- the same syntax works in both msi and dbLoadTemplate(). If you want 
to try out the new msi it should be possible to extract just the 
src/ioc/dbtemplate/msi.c file and build it against a 3.14.12 version of 
Base.

You can also of course use any templating language you like to write 
substitutions. We provide msi which shares the dbLoadTemplate syntax, 
but other sites have written their own tools when they had specific 
needs which msi can't meet. You could modify msi as well, but I would 
suggest starting from the 3.15 version if you think you might want to 
offer your changes back to us.

HTH,

- Andrew

On 11/15/2013 06:15 PM, Brown, Garth wrote:
> I'll add a few tangentially related thoughts on how msi/macLib might
> be modified. It would be nice if there was a way to keep a macro with
> a default value in a template unexpanded. That is, if sample.template
> contains the line
>         field(X, "$(MYX=3)" )
> then sample.substitutions could have a way to indicate that MYX
> shouldn't be expanded and should retain the default value part, so
> that sample.db still had exactly that line. As it is, you can leave
> MYX undefined, which expands to
>         field(X, "3" )
> Or you can have in the substitutions { MYX='$(MYX)' }, which expands
> to
>         field(X, "$(MYX)" )    # default value is lost
> The macro with default can't survive msi unchanged.
> If there were a way to leave the macro undefined with the default
> value intact, I could solve my problem with two levels of
> substitutions files: a general substitutions file that contained
> macros with defaults for everywhere, and environment specific
> substitutions files  that used the output of the general one as a
> template.
> Getting more technical about how that might work, you could interpret
> { MYX=$(MYX) } recursive definition as not wanting the macro
> substituted, rather than as an error condition. Right now, macLib
> will turn this into $(MYX, recursive), indicating an error and losing
> the default value.
> I had a look in macCore.c where this case is handled, and didn't
> immediately see how to implement that. The recursive definition is
> detected one call stack level below where the default value is
> specified.

--
Advertising may be described as the science of arresting the human
intelligence long enough to get money from it. -- Stephen Leacock