nil in numeric context??

[wkitty42]

what does this mean?

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Nasal runtime error: nil used in numeric context

the line pointed to is

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var wpt= wp.getvalue() -1;

[D-ECHO]

I think it means that the value used is not a number

[PINTO]

It means wp.getValue() is evaluating to nil, and the nasal interpreter won't do arithmetic on nil values. You can throw an if-statement right before the line checking if it's nil or not. Something like

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if ( wp.getValue() == nil ) {
   var wpt = -1; # or whatever default value you want
} else {
  var wpt = wp.getValue() - 1;
}


[wkitty42]

interesting... now that i look at these two comments, i didn't think about the "-1" being "minus one"... i saw it as "negative one" but couldn't understand why it would be there... i'll give the "if" statement a try and see how it goes...

[Hooray]

it is referring to the lvalue, the rvalue is the numerical concept - and the lvalue evaluates to a non-numerical nil value, which means that the expression as a whole cannot be evaluated

[wkitty42]

well, i don't get that error any more when the sim starts up... i'm not sure if the value is right but at least there's no error and a property being set seems to be changed as the item is triggered...

[Thorsten]

It's about wp.getvalue().

Say that function looks like

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wp.getvalue = func {

var string =  "No value found";

return string;
}


so then the function evaluates fine, but then

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var wpt= wp.getvalue() -1;

tries to do "No value found" -1 - which doesn't work. Same if the function never assigns any value to the return - then it evaluates to NIL and Nasal can't subtract one from that either.

[wkitty42]

yeah, i have no idea where wp.getValue is created... the error i was seeing was in a craft's systems.nas file... assuming that it is a nasal script that creates it, i don't find it in fgdata, either, so i can't look closer to see why it may be nil... i do know that it is a capital 'V' in "Value", though... i did make that mistake

[Hooray]

It's more like a navdb-related FGPositioned data structure / API (see the navcache article)

[PINTO]

It's route manager related, actually. To find the correct member of the route/wp[] vector that the current-waypoint property is pointing to. This line of code is very common in system.nas in multiple airplanes.

[Hooray]

FYI: The route manager is indeed handling/returning FGPositioned objects (so called Nasal ghosts wrapping FGPositioned smart pointers)