[hiredman]

sorting-by and sorted-grouping-by sorted their facts again on every conversion. Clojure sorted collections cannot hold that state, because they carry a comparator, and a comparator does not serialize.

Change

• clara.rules.accumulators.wb-tree: a sorted bag and a sorted map on a weight-balanced tree (Adams, with the (3, 2) parameters of Hirai and Yamamoto). Every operation is O(log n) in the worst case, and a merge is a split-and-join union.
• No comparator inside. The collections hold no comparator. Each operation that compares takes one as an argument, so the state is plain data.
• The bag keeps every item verbatim, and remove-item removes the newest item that is =.
• sorted-map-view puts a Clojure sorted map over a map and its comparator.
• sorting-by keeps a bag. sorted-grouping-by keeps a map of bags and returns a view.
• Fressian: handlers for the bag and the map. The view is written as a plain map.
• Reader tags: #clara.rules/sorted-bag and #clara.rules/sorted-map.

Behaviour changes

• sorting-by returns a vector. It used to return the ArraySeq that sort-by gives.
• sorted-grouping-by returns a sorted map with vector groups. The old array-map result lost its order with nine or more groups.

Review notes

• Nothing detects a comparator that differs from the one that built the collection.
• bag-vec opens the package-private PersistentVector constructor by reflection, with a fallback. It is about 1.5 times faster than a transient reduce.

Tests

New tests for the tree, Fressian and session durability. make test passes: 1,003 tests, 0 failures.