Re: custom functions or function macros

Mike Weilgart <[email protected]> Fri, 10 Dec 2021 00:01:32 -0800

Newsgroups	gmane.comp.sysutils.cfengine.general
Message-ID	<[email protected]>

Hi Valentin,

If you collect the promises you are writing into a bundle, you may find you don't need to use those functions over and over. Bundles can also be parameterized. However, they are NOT functions. There is no such thing as a user-defined function in CFEngine policy, and the functions that do exist should be thought of more as "helpers" than as imperative actions like you would find in C or Python or most other languages.

CFEngine is declarative, not imperative.

I'm not entirely sure why you would need to check if a hostname is resolvable in the context of writing CFEngine policy; possibly if you give more info on your use case, I (or someone else) could suggest a more idiomatic CFEngine solution.

Incidentally, there is a great tutorial that Aleksey Tsalolikhin wrote a few years ago: https://www.softcover.io/read/72be7d4f/cf3/cfengine_100

It's for a slightly older version of CFEngine 3 than the most recent one, but I recommend it because it goes a long way toward helping you "think" in CFEngine, and approach problems and use cases in the manner best suited to a declarative language. Hope that helps.

Best,
—Mike Weilgart

On Dec 6, 2021, at 7:23 AM, Valentin Kleibel <[email protected]> wrote:

Hello,

I recently came across situation where i need to use the same combination of functions over and over again.
In my case it's to check if a hostname is resolvable:
'not( strcmp( host2ip( $(hostname) ), $(hostname) ) )'

Is there any way to make this a custom function or macro that i can easily reuse?

Thanks for your help,
Valentin

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