This example models a basic delivery trip workflow -- driving to pickup location, item pickup, driving to destination, handing off or dropping off the item, payment.
Example:
(output omitted for brevity)
~/src/delivery $ source ./.env
💙💛 ~/src/delivery $ mix setup
💙💛 ~/src/delivery $ mix phx.server
2025-11-05 10:01:39.848 [info] Migrations already up
2025-11-05 10:01:40.577 [info] Running RsWeb.Endpoint with Bandit 1.8.0 at 127.0.0.1:4000 (http)
2025-11-05 10:01:40.578 [info] Access RsWeb.Endpoint at http://localhost:4000
...
You can now navigate to http://localhost:4000 and start a few deliveries, usher them through, and watch them run their course.
The definition of the workflow can be found in lib/rs/trip/graph.ex, and the example below illustrates running an execution of this workflow, which gets created once the driver and the order get matched.
The workflow is built with Journey, an Elixir package for defining and executing Persisted Distributed Reactive Graphs. In this application, Journey provided:
- persistence (db schemas),
- scheduling one-time and recurring tasks,
- orchestrating conditional events and dependencies,
- structuring the code of orchestration logic and computations,
- retries and crash recovery,
- distributed computations and horizontal scalability.
... which is hundreds of lines of code and a lot of non-trivial complexity that I didn't have to write. Instead, the core of the application is concise (most of the code is in the UI!), resilient, self-documented (see the graph), and naturally scalable. Journey's f_on_save functions generate PubSub notifications which trigger UI updates.
This iex session illustrates creating a new trip, and ushering it through – with logs and function calls.
Once the trip starts, the driver drives to the pickup location. If the food shows up within allotted time (if the driver marks picked_up as true), the driver proceeds to the drop off location. If the customer comes out to pick up the food, the driver sets handed_off, otherwise, the item is dropped_off. At that point, the payment gets collected. That's all!
💙💛 [markmark ~/src/rideshare/rs][simpler-graph][S] $ iex -S mix
Erlang/OTP 27 [erts-15.2.3] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]
Compiling 2 files (.ex)
Generated rs app
2025-11-08 02:23:14.904 pid=<0.296.0> [info] Migrations already up
Interactive Elixir (1.19.1) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> trip = RS.Trip.new("driver1", "order1", 1, 5, 9, 98, "🍕", "America/Los_Angeles")
2025-11-08 02:23:51.907 pid=<0.429.0> [info] Starting a new trip.
Driver: driver1
Current Driver Location: 1
Order: order1
Pickup Location: 5
Dropoff Location: 9
Price: $0.98
Item: 🍕
Started in Time Zone: America/Los_Angeles
2025-11-08 02:23:51.997 pid=<0.453.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving to pickup location 5. Currently at: 1. ETA: in 4.
"TRIP4Y18GX0H69JDXH3122YM"
2025-11-08 02:23:56.174 pid=<0.483.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving to pickup location 5. Currently at: 2. ETA: in 3.
2025-11-08 02:24:01.201 pid=<0.532.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving to pickup location 5. Currently at: 3. ETA: in 2.
2025-11-08 02:24:01.223 pid=<0.550.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving to pickup location 5. Currently at: 3. ETA: in 2.
2025-11-08 02:24:06.236 pid=<0.572.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving to pickup location 5. Currently at: 4. ETA: in 1.
2025-11-08 02:24:11.278 pid=<0.603.0> [info] TRIP4Y18GX0H69JDXH3122YM: Waiting at pickup location 5.
2025-11-08 02:24:11.305 pid=<0.632.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driver is at pickup location 5
iex(2)> Journey.set("TRIP4Y18GX0H69JDXH3122YM", :picked_up, true); :ok
2025-11-08 02:24:15.891 pid=<0.662.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving item to drop off location 9. Currently at 5. ETA: in 4.
:ok
2025-11-08 02:24:16.320 pid=<0.683.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving item to drop off location 9. Currently at 6. ETA: in 3.
2025-11-08 02:24:21.352 pid=<0.717.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving item to drop off location 9. Currently at 7. ETA: in 2.
2025-11-08 02:24:26.388 pid=<0.741.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driving item to drop off location 9. Currently at 8. ETA: in 1.
2025-11-08 02:24:31.424 pid=<0.775.0> [info] TRIP4Y18GX0H69JDXH3122YM: Waiting for the customer to come pick up the item at the drop off location 9.
2025-11-08 02:24:31.450 pid=<0.797.0> [info] TRIP4Y18GX0H69JDXH3122YM: Driver is at dropoff location 9
iex(3)> Journey.set("TRIP4Y18GX0H69JDXH3122YM", :handed_off, true); :ok
2025-11-08 02:24:34.801 pid=<0.820.0> [info] TRIP4Y18GX0H69JDXH3122YM:
Item handed off.
Charging `order1` $0.98, to driver `driver1`.
The trip is now complete.
:ok
2025-11-08 02:24:34.818 pid=<0.835.0> [info] TRIP4Y18GX0H69JDXH3122YM: Notifying pubsub of trip completion
iex(4)> Journey.load("TRIP4Y18GX0H69JDXH3122YM") |> Journey.values()
%{
driver_id: "driver1",
created_at: 1762597431,
started_in_time_zone: "America/Los_Angeles",
order_id: "order1",
location_driver_initial: 1,
location_driver: 9,
location_pickup: 5,
location_dropoff: 9,
price_cents: 98,
item_to_deliver: "🍕",
picked_up: true,
waiting_for_customer_at_dropoff: true,
reached_dropoff_location: true,
waiting_for_food_at_restaurant_timer: 1762597511,
handed_off: true,
current_location_label: "drop off point",
execution_id: "TRIP4Y18GX0H69JDXH3122YM",
driver_location_current_timer: 1762597476,
trip_completed_at: 1762597474,
driver_location_current_update: "updated :location_driver",
waiting_for_customer_timer: 1762597531,
payment: "charged $0.98. pickup `order1`, driver `driver1`",
trip_history: [
%{
"metadata" => nil,
"node" => "trip_completed_at",
"revision" => 138,
"timestamp" => 1762597474,
"value" => 1762597474
},
%{
"metadata" => nil,
"node" => "payment",
"revision" => 134,
"timestamp" => 1762597474,
"value" => "charged $0.98. pickup `order1`, driver `driver1`"
},
%{
"metadata" => nil,
"node" => "handed_off",
"revision" => 130,
"timestamp" => 1762597474,
"value" => true
},
%{
"metadata" => nil,
"node" => "waiting_for_customer_at_dropoff",
"revision" => 125,
"timestamp" => 1762597471,
"value" => true
},
...- Play with this application live: https://delivery.demo.gojourney.dev/
- Source code for this application: https://github.com/markmark206/journey-food-delivery
- Journey docs: https://hexdocs.pm/journey/readme.html
- Journey codebase: https://github.com/markmark206/journey