Overview

************NOTE: this worked example section of the wiki is now out of date as GELLO is currently at R.2. This code will not work in later versions of the editor. We intend to update this section to R2 GELLO soon. ****************

GELLO code will be used to calculate the value of 'Total Cost'. It will retrieve the values from 'Number' and 'Cost' and return the result of one multiplied by the other. Click on the RHS in the pane next to IsCalculated for the 'Total Cost'. Then click on  on the far right hand side of this pane, which is now a white background colour.

1. The first bit of GELLO v.1 code is nearly always this:

   let o:observation = parameter[1]

2. Now let's set up a local variable to hold the value for instances of the archetype where 'Cost' is entered. Add the following code:

   let Cost: Integer =
   if o.isdefined() then
   o.find_observation('1.2').value_asPQ().value
   else
   0.0
   endif

3. Same again for 'Number' - a bit simpler as it is already a number:

   let Number: Integer =
   if o.isdefined() then
   o.find_observation('1.3').value_asReal()
   else
   0.0
   endif

4. Test this code if you like by stepping through it with the Step button 
   
   

5. Next thing is to do the algorithm that produces the result:
    

   let Result: Integer = Cost * Number

6. But 'Total Cost' is a Physical Quantity*, so the result needs to be returned in this form. This line of code just declares what needs to be returned by the GELLO v. 1 expression:

   Factory.PhysicalQuantity (Result, '$')

   

   
   
   

7. So the whole bit of GELLO code in the MO Gello Editor (which in turn is embedded in the MO Template Editor) looks like:
   
   
   
   
8. And the thing running in Preview Archetype:
    
   
   
   
9. Don't forget to save the archetype!!