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Predicate :</2
Availability:built-in
[semidet]+Select :< +From
True when Select is a‘sub dict’of From: the tags must unify and all keys in Select must appear with unifying values in From. 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, _).

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LogicalCaptain said (2020-07-16T21:41:14):0 upvotes 0 0 downvotes
Picture of user LogicalCaptain.

Naming

IMHO, "select" is not the appropriate name here, the more so because "select" is already used to describe the "successfully pick exactly 1 element out of a list" predicate select/3, which should be called "pick/3"...

The name "dict projection" sounds appropriate for this operation

Then the left dict could be called "small dict" and the right dict "big dict" (ok, where's my coat...)

Unit tests for "dict selection"

dict_selection_testing.pl

A simple application

Default parameters which may be overriden with a dict.

dict_selection_application.pl

Make it usable in the head!

Head matching is based on = always, one would have to invent new syntax to not used =, but DictOfHead:<DictOfArgument instead, possibly with anything leftover dumped into a Rest. Not sure whether this would make sense in all cases but it would certainyl be useful as the clause can be written by someone who doesn't know all the details of the passed-in dict.