pub fn open_traversal(
parent: &mut dyn Kernel,
traversal: Traversal,
) -> Result<TraversalStream, String>Expand description
Open traversal against parent’s current values, on any engine
(engines.md §3.6): the cascaded wires and the wires the
sources reference are snapshotted through
the Kernel trait, and the comprehension is evaluated in the
body’s scope, the body’s program with those wires bound, where a
source or predicate resolves every name it can reference and a
tuple’s own elements are layered in front as it is built. Nothing
here needs the opening kernel beyond the snapshot.