@outputs Mass
@persist Array:array
if(first()){Array=entity():getConstraints()}
Mass+=Array:popEntity():mass()
if(Array:count()){interval(10)}

#That should be one way to do it, I believe. First time round it makes the array, 
#then it'll loop for as long as there are entities in the array. Each time it runs it
# finds the mass of the last entity in the list, adds it to the total Mass and deletes 
#the entity from the array.