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Design pattern: Iterator

Description: "Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation."

This pattern can be used with both classes and prototypes.

A straightforward implementation of this design pattern is to define an iterator predicate that enumerates elements using backtracking. This predicate can then be called from meta-predicates such as the de facto standard forall/2 predicate.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the design pattern sample implementation:

logtalk_load(design_patterns('behavioral/iterator/loader')).

Add some books to our collection:

book_collection::(
                add_title('Design Patterns'),
                add_title('Design Patterns in Dynamic Languages'),
                add_title('Analysis patterns')
     ).

<!-- true. -->

Use the iterator predicate to print all titles in the collection:

forall(book_collection::element(Title), (write(Title), nl)).

<!-- Design Patterns Design Patterns in Dynamic Languages Analysis patterns

true. -->