Instantiates a domain variable to its domain values. The order of enumeration is in increasing domain order.
    ?- local domain(weekday(mo, tu, we, th, fr, sa, su)).
    Yes (0.00s cpu)
    ?- X &:: weekday.
    X = X{[mo, tu, th, fr, sa, su]}
    Yes (0.00s cpu)
    ?- X &:: weekday, indomain(X).
    X = mo
    More (0.00s cpu)
    X = tu
    More (0.01s cpu)
    X = we
    More (0.02s cpu)
    X = th
    More (0.03s cpu)
    X = fr
    More (0.05s cpu)
    X = sa
    More (0.06s cpu)
    X = su
    Yes (0.06s cpu)
    ?- indomain(we).
    Yes (0.00s cpu)