[Bug] sorting

[jw-y]

local com = (a, b) -> a >= b
local a = List(0, 0, 0, 0, 1, 1, 1, 1, 1, 1)
b = a.sortWith(com)

expected output:

b = List(1, 1, 1, 1, 1, 1, 0, 0, 0, 0)

got:

b = List(1, 1, 1, 1, 0, 0, 0, 0, 1, 1)

[holzensp]

This is wild! I managed to reproduce. Thanks for the bug report.

[translatenix]

I don't think this is a bug.
The documentation of List.sortWith says:

comparator should return true if its first argument comes before its second argument in the sort order, and false otherwise.

So it should be local com = (a, b) -> a > b instead of local com = (a, b) -> a >= b.

I checked Swift's and Scala's sortWith functions, and they have the same requirement. Swift additionally states that the comparator function must be irreflexive.

[jw-y]

Either case, I don't think this is any way intended.

FYI,
found the location of the bug.

pkl/pkl-core/src/main/java/org/pkl/core/stdlib/base/MergeSort.java

Line 61 in 58ed824

if (comparator.executeWith(array[mid], array[mid], function)) {

first mid should be mid-1

[translatenix]

That indeed looks like a bug. I guess a reflexive comparator function should only give you an unstable/inefficient sort, not a wrong sort.