Used to retrieve the definition of a defined structure, or to enumerate all visible structure definitions.
Visible structures are those which have either been declared locally, exported, or which have been imported or reexported from another module.
    :- local struct(employee(name,age,salary)).
    ?- current_struct(employee, Spec).
    Spec = employee(name, age, salary)
    yes.
    ?- current_struct(Name, Spec).
    Name = employee
    Spec = employee(name, age, salary)
    More (0.00s cpu) ? ;
    Name = suspend
    Spec = suspend(inst, constrained, bound)
    More (0.00s cpu) ? ;
    No (0.00s cpu)
    ?- current_struct(book, Spec).
    No (0.00s cpu)