Expression patterns provide a way to fix the value which has to be bound to the pattern. The expression can either:

• return a single Node
• be a Node generator

The most common expression pattern is the root operator ^, which return the root of the current data graph.

module Organ(int age);
 
// generator that return Organ Node that have an age < than the argument
Node* getYoungOrgan(int ageThreshold){
	yield (*o:Organ, (o[age] < ageThreshold) *) ;
}
 
// get a signle Node/ It could depends on arguments as well
Node getOldestOrgan(){
	return selectWhereMax( (*o:Organ*), o[age]);
}
 
public void run ()
[
	o:getYoungOrgan(5) (>)* getOldestOrgan()  ::> ;
]