The first big insight Henglein brings in the first paper is structural: you can map searches sensibly over products and sums. This is actually a profound thing,

The first big insight Henglein brings in the first paper is structural: you can map searches sensibly over products and sums. This is actually a profound thing, but most folks outside of Haskell circles don't work with ADTs so they don't understand the universal applicability of this insight. It means you can map them over any concrete, acyclic structure. Which means you can sort anything with radix sort.