On Apr 9, 2021, at 4:00 PM, John Rose <john.r.r...@oracle.com<mailto:john.r.r...@oracle.com>> wrote:
The MH combinator for lookupswitch can use a data-driven reverse lookup in a (frozen/stable) int[] array, using binary search. The bytecode emitter can render such a thing as an internal lookupswitch, if that seems desirable. But the stable array with binary search scales to other types besides int, so it’s the right primitive. This may be confusing on a couple of points. First, the mapping function I’m talking about is not a MH combinator, but rather a MH factory, which takes a non-MH argument, probably an unsorted array or List of items of any type. It then DTRT (internal hash map or tree map or flat binary search or flat table lookup or lookupswitch or any combination thereof) to get an algorithm to classify the array or List elements into a compact enumeration [0,N). Second, when the input array or List is of int (or Integer) then it *might* be a lookupswitch internally, and I’m abusing the terminology to call this particular case a lookupswitch. But it’s really just a classifier factory, whose output is a MH of type K → [0,N) for some K. The output might also be ToIntFunction<K> for all I care; that can be inter-converted with a MH.
