Better unordered folds?

I'm not a huge fan of the way we implement unordered folds. The compiler has no clue what they're up to, so optimization is garbage. I experimented with using an operation

viewU :: BinomHeap a -> Maybe (a, BinomHeap a)

which extracts the root of the first binomial tree, to implement foldlU'.

Unfortunately, the performance was worse than what we do now. But I wonder if things might change if we work in bigger chunks. For starters, something like

viewU2 :: BinomForest (Succ Zero) a -> Maybe (a, a, BinomForest (Succ Zero) a)

Working with two elements at once should reduce the churn in the low bits, and might give this technique some hope.

Inizia con l’implementazione esistente di unordered-fold e con i punti di ingresso denominati foldlU', viewU e viewU2. Confronta l’approccio attuale con l’elaborazione di due elementi alla volta; il lavoro è completato quando si determina se la tecnica proposta migliora le prestazioni e, in tal caso, la si applica all’unordered fold.