The FFI adapter, backed by postgresql-libpq.

adapter bundles the three functions that produce a Connection whose fields are closures over the underlying C-backed PGconn. Result and Cancel values are constructed the same way, closing over the underlying PGresult/PGcancel.

Each closure is a near-mechanical delegation to the matching Database.PostgreSQL.LibPQ function, with the only work being the conversion between this family's portable types (OIDs as Word32, indices as Int32, the shared enums) and postgresql-libpq's C-specific newtypes.