Copying a global reaction

[toggledbits]

The result of push is an array.

[LibraSun]

@toggledbits said in Expressions and LuaXP Functions:

The result of push is an array.

But if you

push ( [ ] , 1 )

shouldn't you get [ 1 ]? And not [ [ 1 ] , [ 1 ] ]?

[toggledbits]

It depends on what the complete expression is. Remember that the value of each is every non-null expression result during the iteration. So an array of arrays is a very possible response.

[LibraSun]

@toggledbits Unless I'm mis-reading the way each works, I had anticipated the underlying interpretation of:

b=[],each i in a=[1,2]: do push(b,i) done

to be as follows:
"Start with an empty array named b. For each item in the array named a, starting with 1, append that value into array b. First, you would get [ 1 ], and the next iteration, using the 2 from a, append that to b to yield [ 1 , 2 ]."

Any I missing an important piece of the puzzle? (I do recognize that do/done is not necessary here, but I left it in for direct comparison with the expression immediately preceding.)

Thanks. Sorry to give you grief over these operations.

[toggledbits]

If you want to see what b looks like at the end, you need to do this:

b=[],each i in a=[1,2]: do push(b,i) done, b

If you don't (which is how you've done it so far), you are seeing the result of each, which is an array, and since each expression within the each has resulted in an array, the result of that each is therefore an array of arrays, and referring to the same array by reference.

[LibraSun]

Makes perfect sense now. Thanks!

[LibraSun]

This one seems to evade the purpose of isnull() somehow:

isnull(1/a) // returns false

whereas

isnull(a) // returns true, as expected

In both cases, a is undefined.

I also cannot seem to create an expression that results in true for isNan(), no matter what I throw at it.

Finally, why would bool(null) return TRUE?

[Elcid]

isNaN([1,2,3]) and isNaN("ten"/2) and isNaN("ten" + "eight") are all true

[toggledbits]

null coerces to zero (0) for arithmetic operations, so 1/null is infinity which is not null.

int("abc") results in NaN which will return isNaN(int("abc"))==true

bool(null) should return false and I will fix it.

Edit: just to follow up, I've added Infinity as a keyword/value to the grammar, with a supporting isInfinity(value) test function (you can also test via value === Infinity), and added that to the documentation for the next release/build. And bool(null) is fixed. FYI, bool() takes a slightly deeper view of "truthiness" than JavaScript natively: the values (number) 0, null, empty string ("") and NaN are false as in JavaScript, but so additionally in lexpjs/Reactor are string "0", string "no", string "off", and string "false"; any other value of any type is true (including empty arrays and objects).

[LibraSun]

MSR RECIPES: Compact object-based message composer

Several of my Rules send out SMTP emails, and I'm always looking for a compact method of composing these outbound messages, using the fewest expressions along with a simple "mail merge" template. Here's a two-variable approach you might consider:

msgBody ► "This is my message." 
// leave blank if msgBody will be set by other Rules

msgTemplate ► 
tmp = {hdr:"Header here" ,  msg:msgBody ,  ftr:"Footer here" ,  crlf:"\n"},
send = {message:tmp.hdr+tmp.crlf+tmp.msg+tmp.crlf+tmp.ftr} , send.message

I hope this can be adapted to your workflow somehow!

[LibraSun]

This post is deleted!

[LibraSun]

Can someone please explain how you would create an array within a Rule that does the following:
(a) begins with an expression that is an empty array;
(b) has another expression containing the .dim_level of a given light;
(c) each time the Rule sets (activates/triggers), the value of (b) is pushed into (a)

Working example:
First time light gets turned on, the rule runs. Dim level of 50 is pushed onto end of [ ], making it [50].
Next time light turns on, the rule again runs and pushes the dim level of 75 onto array, making it [50,75].
Etc.

I can't quite grok where to put my push ( ). In a [Set Variable] using ${{ }} substitution? In an auxiliary Expression? (I've attempted this approach and can only get one iteration along, meaning the array stops growing after 1 element.) And how does one declare an empty array inside an Expression that will otherwise be modified by the Rule, which normally requires it to be blank?

Thanks!

@toggledbits , to put this more succinctly, I find myself unable to implement in MSR the construct you laid out here for creating a time series.

[LibraSun]

SOLUTION: This works for creating a timed data series in MSR...

test1 := if go=="1" then push( test1 , getEntity( "vera>device_110" ).attributes.dimming.level , 5 ) else test1 endif

...BUT...

you must first pre-populate the test1 variable with an empty array [ ], SAVE, then paste in the above definition. Otherwise, MSR will throw a "no such 'push' function on (null)" error! (I call this the "Chicken and the Egg" conundrum, whereas Reactor for Luup doesn't complain about doing push to a non-existent array; it just invisibly creates one for you.)

In my set reaction, I do a [Set Variable] [ go ] = 1, and in the reset reaction [Set Variable] [ go ] = 0, with an Interval imposed on the Rule's sole Trigger condition, making it go TRUE for 2 seconds every 60 seconds.

NOTE: Interestingly, with Interval limited to 3 repeats, the variable go changes to "1" only 3 times (expected), yet somehow the array gets fully populated with 5 values (unexpected), so I must not fully understand the leading- and trailing-edge nature of Interval as it applies to Expression re-evaluation. I'm sure @toggledbits will elucidate? Or is this truly unexpected behavior?

ANSWER: Unchecking "Force re-evaluation of expressions and conditions" in both the set and reset reactions cured the problem of "too many data points". There was my problem.

[toggledbits]

@librasun said in Expressions and LuaXP Functions:

you must first pre-populate the test1 variable with an empty array

You don't actually. This is just a bug in lexpjs. I've fixed it in my local copy, will be in the next build. It's just this simple:

[LibraSun]

@toggledbits Do you want to include conditional key references like this in lexpjs?
obj={'122':['a',5, true]}
obj?['123'][0] // null or throws error
obj?['122'][0] // (string) "a"

By this I mean do you want to have square bracketed key references treated the way potentially non-existent dot references are handled using question marks.

[toggledbits]

Confused. Are you asking for this to be added?

[LibraSun]

I think so, if it's possible. Just wanted to (a) make sure that ?[ doesn't exist yet (my testing seems inconclusive), and (b) you consider it necessary. I've already bumped into a potential use case.

So, I suppose "Yes, add it" at least for consistency with existing ?. usage.

[toggledbits]

@librasun OK... so I think I'm seeing through the confusion now...

The ?[ and ?. operators already exist; they were added together with ?? a long time ago. They are left-associative, so they refer to the operand on the left. In your examples, they will not work as you are trying to get them to because obj is non-null in every case (it's the first thing defined in the example). I think what you mean to say is:

obj={'122':['a',5, true]}
obj['123']?[0] // which will return null and not throw an error
obj['122']?[0] // which will return (string) "a"

[LibraSun]

Agree with everything you just wrote. I was mis-applying the question marks, as far as placement in my expression (treating it as a prepend instead of append). Thanks for straightening me out yet again.

I had mistakenly thought this construct only worked on objects.?with.?arbitrary.?keys and arrays[with_arbitary_indexes]? and not object keys (with non-standard names) referred to via brackets. My bad.

[LibraSun]

CODE SAMPLE: Creating an Array of N Whole Numbers [0, 1, ... , N]

Sometimes you need an array of Counting Numbers from zero to some arbitrary integer N. But it's hard to write this as an Expression in MSR, because you don't know in advance how long to make the array, and the value of N may change later.

This somewhat byzantine construct fills the bill, and works for N=0 up to N=56:

arrCount := N=56,each s in keys(substr((s='s'+1/9)+s+s,0,N+1)): int(s)

This example evaluates to the array:

arrCount == [0,1,2, … ,55,56]

Just change the number after N= (it could also be another variable name, of course!) to suit your needs.

BONUS: Need more numbers? Just add another +s in the middle for an additional 19 integers (giving max. N=75). Repeat indefinitely!

P.S. @toggledbits I may need to enter this in the Obfuscated Lexpjs Code contest!