Trying to program rule DSL not working at all

Setup, Configuration and Use Scripts & Rules
1

Hi all,

I am new to openhab, but for 30+ years programming in different languages (Fortran, Pascal, Assembler, C/C++, some Java). I have an issue getting ANY rule DSL running, even the examples quit with errors (which is quite strange for me.). I am running OH3 (latest stable) in Portainer on Asustor, everything else works fine, rules clicked together with “when” … “then” from the UI are working fine.

What is my basic problem here? I checked the documentation, I tried the sample snippets, nothing is working.

Example:

var Timer T = NULL

T = createTimer(now.plusSeconds(5), [ |
logInfo(“rules”, “Timer activated”)
//Do something…
])
logInfo(“rules”, “Timer created”)
T = NULL

throws errors:

2021-11-04 13:28:49.512 [ERROR] [internal.handler.ScriptActionHandler] - Script execution of rule with UID ‘1f41eb55cb’ failed: var Timer T = ___ NULL

T = createTimer(now.plusSeconds(5), [ |
logInfo(“rules”, “Timer activated”)
//Do something…
])
logInfo(“rules”, “Timer created”)
T = NULL

  1. Type mismatch: cannot convert from UnDefType to Timer; line 1, column 14, length 4
  2. Type mismatch: cannot convert from UnDefType to Timer; line 8, column 211, length 4
2

NULL is a state-type object, something you can set an Item state to.
You can’t set a Timer type object to a state type value.
What you intended was null, the void placeholder in DSL.

But if you look at your code, you don’t need this T at all. You set it null, create a timer, set it null again.
Just create an anonymous timer.
createTimer(now.plusSeconds(5), ...

3

Thanks for your quick and helpful answer, just tested, and it works. I assumed it should work this way because I used exactly the code which is provided with OpenHAB. I did not see that NULL != null.

4

somewhere else here i found a explanation that i noted for me:

// NULL (==) is a state that indicates that an Item is uninitialized.
// null (===) is something that is only meaningful in Rules and means a variable doesn’t have a value.
5

Thanks, that difference is clear. But what is still confusing to me is that the example code snippets throw errors. E.g:

var Timer myTimer = null

rule "timer example"
when
    Item YourItem changed

results in:

Script execution of rule with UID ‘1f41eb55cb’ failed: var Timer myTimer = null

I need to reference the timer (the anonymous version works, but it’s not the one I need), can pls anyone explain why the given examples seem to be “wrong”?

6

You cannot copy-paste DSL rules intended for xxx.rules file usage into GUI entered rule action script section. The GUI manages all the when-then-end stuff, you only need the body.

You can’t in GUI based DSL. (There is nowhere “outside the rule” to define ‘globals’)

7

Personally I find it a lot easier to ignore the rules DSL and instead use habapp - HABApp - Easy automation with openHAB

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8

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