[Solved] Local expression in Rule does not evaluate as they used to do

[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!

[toggledbits]

I think it's a grand prize winner for the "Solutions for Problems Nobody Has Ever Had Using Reactor" contest, for sure, but I'll admit it's not a straightforward problem to solve without a counting loop structure, so the question is, what's the best approach:

1. Implement a counting loop statement (for in many languages);
2. Take the Python-ish approach and have either a range() function or a start..end range operator, which you could use as the operand in each;
3. Other?

Choice 2 is better suited to an expression environment, but we already ride the fine edge with each, first and do statements in the current language. But in keeping with the flavor, each of these statements still produces an expression result, so still arguably as much operator as statement; it's less clear what a sensible return result from "for" might be. On the other hand, #2 requires an array be built in memory over which to iterate, and an error could easily build a large array that consumes dangerously large amounts of (or all) available memory and have a negative impact on stability (so perhaps more safeguards in order, but how big is too big?).

EDIT: I just prototyped the two options given above:

# Example for to build array of values 1-25
arr=[]; for i =1,25: push(arr, i)
# That's unnecessarily clunky and could be streamlined by making "for" return an array
# of result values like "each":
arr=for i=1,25: i
# But then... that means "for" is about the same as "each", just different operands.
# In my mind, that kind of argues for option 2:
arr=each i in range(1,25): i
# or
arr=each i in 1..25: i
# and even that's unnecessary, because you could just do
arr=range(1,25)
arr=1..25
# because both of those naturally return an array.
# Another example, to sum all the values from 1 to 25 it would be:
sum=0; for i in 1,25: sum=sum+i
sum=0; each i in range(1,25): sum=sum+i
sum=0; each i in 1..25: sum=sum+i

I think the range operator .. is the cleanest all around, and relieves the ambiguity of having both for and each so similar. I'm not sure .. is any easier or harder to learn/remember than having a function range(start,end). So I'm leaning toward option 2 with range operator ...

[LibraSun]

100% agree that sum=0; each i in 1..25: sum=sum+i makes the most sense in terms of conciseness without introducing another function name. I don't foresee any usability issues with an m..n operator generally.

I'd expect .. to accept any integer, – or +, for its arguments m and n, regardless if m>n or n>m. Use cases include step functions or monotonic sequences for things like dimming levels over time.

Sure looks better than what I came up with, eh?

Glad I brought it up, because I had recently been hand-coding my own arrays for use with each.

[LibraSun]

@toggledbits For today's checkup on how Expressions handle assigning values by reference, I constructed:

a=b=c=[1,2,3], pop(a), shift(b), [a==b,b==c,a==c,c]

// result is [true,true,true,[2]]

A. Pls confirm this is as expected. (I'm guessing 'Yes')
B. Does result comport with typical user's expectations? (I'm guessing 50/50)
C. I know you don't want me mashing that "Try" ► button (in lieu of actual, useful, runtime evals).

Just something that's been on my mind, wondering if it belongs in your Test Suite.

[toggledbits]

You can't compare arrays (or objects) with ==. What it's telling you when you write a==b is that neither a nor b are null, 0, or false, and they are identical references. So yes, this is all expected.

As for it comporting with user expectations, if the user is a programmer, I think this will be no surprise. Non-programmers have the learning curve. Again, another reason I really don't like guiding users to expressions. New users, IMO, should be blissfully unaware of their existence.

[LibraSun]

Wise words!

[toggledbits]

By the way, I forgot to mention, as is often necessary in many languages because of the reference issue, there is a clone() function that makes a new copy of an existing array or object. So a=[1,2,3],b=clone(a),push(b,99) will result in a having [1,2,3] and b having [1,2,3,99].

[LibraSun]

It's as if you read my mind. I suppose my numerous "cloning arrays" examples gave it away.

Without clone(), I was never (easily) able to manipulate a copied array without affecting the original, and that was driving me bonkers.

Thanks!