Services and the edge

A service is an interface for domain dependencies, emitted as a Context.Service class (§16 shows both sides). Users! yields the live implementation. Wiring implementations uses standard library code without dedicated syntax: layers are written with Layer. Layer is the one Effect namespace Hem does not auto-import (the other namespaces in this tour are inferred from usage); import it explicitly with import { Layer } from "effect":

let UsersLive = Layer.effect(Users, effect {
  let db = Db!
  makeUsersService(db)
})

And the edge of a Workers app is one pipe chain in a route module:

export let loader = ({ params }: Route.LoaderArgs) =>
  getUser(params.userId) |> Effect.provide(AppLayer) |> Effect.runPromise

If a required service is omitted, the compiler reports which services are missing and where they were introduced, rather than emitting TypeScript’s Type 'Users' is not assignable to type 'never'.