Question

I need to learn concurrently when a turtle changes its heading. Namely, when the turtle changes its direction, a procedure or a reporter will change the value of a boolean. But this reporter won’t be called by any other procedures, it will be always running (checking turtle’s heading) while the turtle is moving. Is there any way of this in NetLogo?

Answer 1

I think you can achieve something similar to what you want with a “forever” button: that is, a button that runs a procedure constantly. (People usually have at least one button like that, typically named “go”, in their models.)

Assuming the heading you want to track is that of turtle 0, you can have code like this:

globals [
  current-heading
  heading-has-changed
]

to check-heading-changes
  if [ heading ] of turtle 0 != current-heading [
    set heading-has-changed true
    set current-heading [ heading ] of turtle 0
  ]
end

To have the check-heading-changes code run constantly, you just need to call it from a “forever” button:

You have to remember to click the forever button when you want to start the monitoring. Now, of course, the code above also assumes that you will have some other procedures running that controls the turtle, and also that will actually do something (and reset the variable) when heading-has-changed becomes true.