Lamdba in rules file

[Garbisa]

Is it possible to use Lambdas which are defined in another rules files?

[Garbisa]

Design Pattern: DRY, How Not to Repeat Yourself in Rules DSL

Please see Design Pattern: What is a Design Pattern and How Do I Use Them for details on what a DP is and how to use it. Problem Statement Do Not Repeat Yourself (DRY) Often an inexperienced programmer will find that a naive and straight forward approach to writing Rules DSL Rules results in a lot of duplicated code. Often experienced programmers find that the usual tools to avoid duplicated code like data structures and classes are not available in Rules DSL and they end up fighting the lang…

So Lambdas are not useful for my situation. I will go with Proxy Items

[rlkoshak (Rich Koshak)]

@Garbisa

So Lambdas are not useful for my situation. I will go with Proxy Items

I’ve never tried it and can’t guarantee it will work, but theoretically you should be able to put a lambda into the shared cache. Back when I wrote that post there wasn’t a shared cache. See Textual Rules | openHAB.

I can’t remember if it was added to Rules DSL before or after 3.4 release so if you see errors saying sharedCache is not defined you’ll have to wait for OH 4 to use it.

But IMO if you are heading down this path it’s a strong indication you’ve outgrown Rules DSL and one of the other languages might be a better fit.

[Garbisa]

Thanks for your remarks.
Do you have some lines of code how to use the “shared cache”?

[rlkoshak (Rich Koshak)]

I linked to the docs that talk about the shared cache which includes

For further documentation on using the cache see here

which includes examples. Do you have specific questions after reading those docs and examples?

[infohills]

Some rule languages might not offer direct support for referencing lambdas across files. In this case, you have two options:

• Define the Lambda in Each File: This can lead to code duplication, but ensures your rules function independently.
• Create a Function Instead: If the lambda is complex, consider defining it as a full-fledged function within the same rule file. This promotes reusability without relying on external definitions.

[rlkoshak (Rich Koshak)]

@infohills

Some rule languages might not offer direct support for referencing lambdas across files

Believe this is true for all the supported rules languages. A lambda is an anonymous function and as such it is really not sharable. A lambda can be assigned to a variable to de-anonymize it but except in Rules DSL which doesn’t support functions at all, you may as well just define a function in the first place.

And if you’ve defined a function that you want to use across multiple files, you may as well put them into a library you can import into your various files. JS, jRuby, and Jython all support this. Rules DSL does not.