code: def add_incomplete(var_name, dependencies):
      
      warnings.warn('%s has no equation specified' % var_name,
                    SyntaxWarning, stacklevel=2)
  
      # first arg is `self` reference
      return "functions.incomplete(%s)" % ', '.join(dependencies[1:]), []
docs: Incomplete functions don't really need to be 'builders' as they
       add no new real structure, but it's helpful to have a function
       in which we can raise a warning about the incomplete equation
       at translate time.