This function is used at runtime to get the actual type of the values produced by the given rule at runtime.
For data type rules, the name of the declared return type of the rule is returned (if any),
e.g. "INT_value returns number: MY_INT;" returns "number".
This function is used at runtime to get the actual type of the values produced by the given rule at runtime. For data type rules, the name of the declared return type of the rule is returned (if any), e.g. "INT_value returns number: MY_INT;" returns "number".