Problem with functions in data tree

Hi,
I’m trying to use functions in my problem type, but they don’t work, even using the example of the customization manual, it is supposed to appear like this
Captura de Pantalla 2019-08-22 a la(s) 18.00.40.png
But data tree shows this,


This is the code as it is in the text. in the .spd file

In the .tcl file

proc MyDensityFunction { domNode args } {
set result [join [list scalar

  • ] ,]
    return $result
    }