An unary predicate enables the use of boolean methods as patterns. The methods needs to:

• return a boolean
• have at least one argument, and its first argument is of type Node (or extend Node)

Such a method is called on the Node tested, and will use it as an implicit argument. The type of node is also implicit from the method argument.

module Organ(int age);
 
boolean isAge(Organ o, int i){
	return o[age] == i;
}
 
public void run ()
[
	o:isAge(5) isAge(6) ::> ; // o is an Organ of "age" 5 which have a successor Organ of age 6
]