Cost me a little time to figure out what was going on.
18 * -2 = -2
18 * (-2) = -36
18 * 2 = 36
I can work around this obviously, but is that a bug?
Arithmetic operators in an expression... Why does 18 * -2 = -2?
pnbruckner
#3
Sounds like a bug. My guess is it’s putting a zero between the * and -, so “18 * 0 - 2 = -2”. But that’s just a guess.
bangali
#5
@ipaterson looks like evaluate expression is not handling the special case of operand followed by a negative number and treats the - as an operand instead.
ipaterson
#7
To at least explain the result, this is getting evaluated as
| +240ms | ║2.0 * 0.0 |
|---|---|
| +247ms | ║0.0 - 1.0 |
I can’t promise anything here since the code that evaluates expressions is very complex but if it turns out to be an obvious fix I’ll give you folks something to test 
ipaterson
#8
The expression 2 * -1 resulted in these three expression components:
| +200ms | ║║item [t:integer, v:2, d:0, o:*] |
|---|---|
| +200ms | ║║item [t:null, v:0, o:-] |
| +201ms | ║║item [t:integer, v:1, d:0, o:+] |
As far as I could tell, this unary negation was always represented by t:null regardless of whether it was followed by a number, a variable, or other. The correct fix seems to be changing line 5384 of the webCoRE Piston Smart App from
if (((item.o) == '!') || ((item.o) == '!!') || ((item.o) == '~')) break;
to
if (((item.o) == '!') || ((item.o) == '!!') || ((item.o) == '~') || (item.t == null && item.o == '-')) break;
I am out of time today, would anyone like to try out this tweak with a variety of expressions?
ipaterson
#9
This should be fixed in today’s v0.3.104.20180323 release which will require updating your smartapps at ide.smartthings.com and possibly hard refreshing the dashboard.