Why OTP for multi-surface apps

Most UI frameworks implement crash recovery with try/catch, state management with global stores, concurrency with goroutines or async/await, distribution with gRPC. Raxol gets all of that from OTP.

The natural mapping

OTP concept	TUI equivalent	What you get
GenServer	Elm update loop	`init/1 -> update/2 -> view/1`, managed by the runtime
Process	Component	Each Component can run in its own process
Supervisor	Crash recovery	A Component crashes, it restarts. The rest of the UI doesn't notice
Hot code swap	Live reload	Change `view/1`, save, running app updates. No restart
`:ssh`	SSH serving	Built into Erlang. No dep, no daemon, just `:ssh.daemon`
`libcluster`	Node discovery	Gossip, DNS, Tailscale. Nodes find each other automatically
`send/2`	Inter-component messaging	No event bus library. Just processes sending messages
ETS	State management	Fast shared state without serialization overhead

These aren't analogies. They're the actual implementations.

What this means in practice

Crash isolation

In Ratatui or Bubble Tea, if a component panics, your whole app dies. In Raxol:

process_component(UnstableWidget, %{path: "/dev/random"})

The supervisor restarts the component and renders the next frame. OTP was built for this.

There is one place this stops. On Unix and macOS the terminal backend is a termbox2 NIF, and a NIF runs inside the VM's own address space. Segfault there and the whole node goes down, supervisor or not.

The blast radius is small, though. That NIF only draws: cell writes, cursor moves, present. Input never touches it. Keystrokes arrive over OTP's own prim_tty, and a canary in CI watches that path in case OTP moves it. Windows skips the NIF entirely and falls back to the pure Elixir IOTerminal, so nothing native is loaded there at all.

When the VM does die that way it dies without putting your terminal back. Run reset; there is a note in the quickstart.

Hot reload

Erlang's code server supports hot swapping at the module level. Save a file, and the running app picks up the new view/1 on the next render cycle. No reconnection, no state loss. Same mechanism that lets telecom switches upgrade without dropping calls.

SSH serving

Erlang ships with a full SSH server. Raxol wraps it:

Raxol.SSH.serve(MyApp, port: 2222)

Each connection gets its own Lifecycle process with its own state. The whole thing is 4 modules, ~400 lines, because the hard part is in Erlang's :ssh.

Textual added SSH in 2024 via textual-serve, wrapping an external library. Bubble Tea and Ratatui have community wrappers.

Distribution

BEAM was designed for distributed systems. Raxol's swarm module builds on that:

Raxol.Swarm.Discovery.start_link(strategy: :tailscale, node_basename: "raxol")
Raxol.Swarm.TacticalOverlay.update_entity(:unit_1, %{position: {10.0, 20.0, 0.0}})

Nodes are BEAM nodes. Messages are Erlang messages. CRDTs merge with pure functions.

Three rendering targets

A TEA module is init/1, update/2, view/1. The rendering target is a runtime decision:

Terminal: Lifecycle renders to a screen buffer, diffs, writes ANSI
Browser: Raxol.LiveView.TEALive hosts the same module in Phoenix, bridges events
SSH: Raxol.SSH.Session wraps Lifecycle per-connection

One app, three outputs.

AI agents

An agent is a TEA module where input comes from LLMs. Same init/update/view, same supervision. The framework is ~300 lines because most of it is OTP:

Agent.Session is a GenServer wrapping Lifecycle
Agent.Team is a Supervisor
Agent.Comm is GenServer.call/cast with Registry lookups
Agent.Backend.HTTP is Stream.resource over SSE

Agents are processes. Teams are supervision trees.

The tradeoff

Raxol is slower per-operation than Rust (Ratatui) or Go (Bubble Tea). Buffer creation is 25us vs 0.5us. But a full frame still completes in 2.1ms, leaving 87% of the 60fps budget for your code. Numbers and methodology are in Benchmarks.

You give up raw microbenchmark speed. You get process isolation, hot reload, distribution, SSH, and multi-target rendering. For anything that has to keep running while you change it, that's a good trade.