dimava

    FUNC FACT (N);
       NAMES: P;           (* variable names *)
       1 -> P;
       FOR I FROM 1 TO N ::
          P * I -> P
       DONE                (* endif *)
    RET: P                 (* return value *)
    END;                   (* end of function *)
    
    FOR N FROM 0 TO 6 ::
       ? "FACT(", N, ") = ", FACT(Н)   (* print *)
    DONE;

    const CatDog = { bark(){}, meow(){} }

    const TreeCat = { bark: "oak", meow(){} }

    type A = { bark: fn, meow?: never } | { bark?: never, meow: fn }
    type B = { species: "dog", bark: fn } | { species: "cat", meow: fn }
    or use instanceof with a class