package gve.calc.formula;

 In the future, we will replace all functions by unary prefix operators.
  This has the advantage that we can alter their appearance; e.g.
  subst(t,x,alpha) can appear as [t/x]alpha, idem for summations, integrals etc. 

public interface Function {
	
 Args may not been evaluated, so we need eval to do this. 
	public Part call(String funcname,Part args,Evaluator eval);
}