Caqti_lwt_unix.PoolSourceval use :
?priority:float ->
('a -> ('b, 'e) result Lwt.t) ->
('a, 'e) t ->
('b, 'e) result Lwt.tuse f pool calls f on a resource drawn from pool, handing back the resource to the pool when f exits. The result returned by f is not used by Caqti, but allows flattening errors into a single polymorphic variant type.