Here is a simple example, that finds all men in the working memory:
Man( $toy: /wife/children[age > 10]/toys )
For each man it navigates the wife reference then the children reference; the children reference is a list. For each child in the list that is over ten it will navigate to its toy's list. With the XPath notation if the leaf property is collection it will iterate it, and the variable binds to each iteration value. If there are two children over the age of 10, who have 3 toys each, it would execute 6 times.
As it traverses each reference a hook is injected to support incremental reactivity. If a new child is added or removed, or if an age changes, it will propagate the incremental changes. The incremental nature means these hooks are added and removed as needed, which keeps it efficient and light.
You can follow some of the unit tests here:
It's still very early pre-alpha stuff, but I think this is exciting stuff.