Sorted in Hylang reports as being a built-in but isn’t documented in the HyLang built-in documentation. After a bit of head-scratching I realised that this is just the Python built-in sorted.
Hy uses keyword parameters to bind keyword arguments in Python interop so to define a new sorting function you assign a lambda to the key keyword.
So to sort pairs by the second value…
(sorted :key (fn [[a b]] b) items)
This is pretty similar to Clojure’s sort-by except that you can’t define the comparator explicitly.