Problem with functions in data tree

[dsvivass]

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 (23.47 KiB) Viewed 17717 times

But data tree shows this,

Captura de Pantalla 2019-08-22 a la(s) 18.00.25.png (53.79 KiB) Viewed 17717 times

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

<value n="dens" pn="Density" min_two_pnts="1" help="Density of Steel" unit_magnitude="M/L^3" units="kg/m^3" function="[density_function]" function_func="" v="1.0">
<function>
<functionVariable n="interpolator_func" pn="Interpolation function" variable="x" units="°C">
<value n="point" pn="Point" v="20.0,7830.0"/>
<value n="point" pn="Point" v="600.0,7644.0"/>
</functionVariable>
</function>
</value>

<procs>
<proc n='density_function' args='args'>
<![CDATA[
MyDensityFunction $domNode $args
]]>
</proc>
</procs>

In the .tcl file

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

• ] ,]
  return $result
  }