How to implement enum restriction?

[ConstantinVasilev]

I tried with the below code without success. The documentation also has example where the in condition is treated as creation of records/instances rather than a constraint.

%%logica Dog

@Engine("duckdb");

# Generic Dog abstraction: something with name and breed which can take only 2 values
Dog(name:, breed:) :-
    breed in ("shepherd", "bulldog");


# Valid dog instance
Dog(name: "Fido", breed: "shepherd");

# Invalid dog instance
Dog(name: "Fido", breed: "sausage");

[EvgSkv]

For now Logica does not have enum types, but this kind of check can be done at runtime, using Error function as follows.

@Engine("duckdb");

# Generic Breed abstraction: something which can take only 2 values
Breed(x) = x :-
  Constraint(
      if x in ["shepherd", "bulldog"] then
        true
      else
        Error(x ++ " is not a breed.")
  );

# Valid dog instance
Dog(name: "Fido", breed: Breed("shepherd"));

# Invalid dog instance
Dog(name: "Fido", breed: Breed("sausage"));

CoLab: https://colab.research.google.com/drive/1iFbEp6iam0FXoZELukzDLbkHIIVJxkVT?authuser=1#scrollTo=uZ1cdHNW7ETp

There is no way of having a rule that would do checks on other rules (other than with types as discussed in the other thread).