(:<)/2

Availability:built-in

[semidet]+Select :< +From

True when Select is a‘sub dict’of From: the tags must match and all keys in Select must appear with unifying values in From. Two tags match if the unify or one of the tags is the reserved # tag. From may contain keys that are not in Select. This operation is frequently used to match a dict and at the same time extract relevant values from it. For example:

plot(Dict, On),
  #{x:X, y:Y, z:Z} :< Dict =>
    plot_xyz(X, Y, Z, On).
plot(Dict, On) :-
  #{x:X, y:Y} :< Dict =>
    plot_xy(X, Y, On).

The goal Select :< From is equivalent to select_dict(Select, From, _).