class IsBoolCompositeAttribute <string attr_name, string val>:
  IsCompositeAttribute<attr_name, BoolAttr, val>;

// Receives a composite DictionaryAttr as an argument and checks if has a
// StrAttr with the name `attr_name` and value `val`.
class IsStrCompositeAttribute <string attr_name, string val>:
  IsCompositeAttribute<attr_name, StrAttr, "\"" # val # "\"">;