code: public FunctionInputDef addVarDef( IVarDef varDef)
      {
      assert varDef != null;
      assert varDef.getName() != null;
  
      if( findVarDef( varDef.getName()) >= 0)
        {
        throw new IllegalStateException( "Variable=" + varDef.getName() + " already defined for function=" + getName());
        }
      
      vars_.add( varDef);
      return this;
      }
docs: Adds a new variable definition.