Re: "Macro" expansion

On Thu, 24 May 2001, Will Partain wrote:

> > 2) Currently we can look up into certain tables ...
> > . It would be Really Nice if we could do this for any
> > arbitrary table field, not just ark-dirs.
>
> You can.  See example below.

Won't this only work for teams and hosts (not packages etc.)?

> You'll help me write the semantics part of the ARK conf-lang
> for this :-?

;-)

I notice Jonathan is looking at bashing at this code, so it might be worth
discussing what could be done. I was thinking of something along the lines
of:

@<object-type|param>:<field-name>[:<index>[:<separator>]]@


Soooh....for hosts:


@host:PERL@             : would return the string in the PERL *string*
                          field

@host:ip-addresses:0@   : would return the string in item 0 of the
                          ip_addresses *list* field

@host:ip-addresses:*:,@ : would return a comma separated list of all the
                          items in the ip_addresses *list* field

@host:ark-dirs:FOO@     : would return the string in entry indexed by
                          'FOO' in the ark-dirs *table* field

Of course all these evaluations are subject to the usual constraints
rules. If you really scary semantics (maybe not a good idea):

@host:describe()@	: would return the output (or evaluate??) the
			  describe method.

Maybe even better would be a syntax with a different opening and closing
symbol (eg. @{blah}@) would be better as it would allow one to nest
macros:

@{host:run-level-dir:@{param:RUN_LEVEL}@}@

Scary stuff...

Matt