As discussed #25 (comment), we need to resolve if, and how, we should specify a sort order when returning unique values.

A corollary issue is, if we support an optional keyword to return sorted unique values, whether we should also support specifying the sort direction (ascending vs descending).

We could limit sorting to ascending order, but that this may be considered an arbitrary restriction may lend support for the argument of not returning ascending/descending sorted output at all. Instead, punting sorting to userland, where sort order can be specified via sort(). However, as discussed in the OP, combining unique/sort may allow implementation perf optimizations which cannot be replicated when performed as two separate steps.