Proof of concept: a Relm4 (GTK4 / libadwaita) process that acts as an Erlang foreign node, controlled by a Gleam process over the Erlang distribution protocol.

Gleam (beam)  ── cookie + epmd ──►  Relm4 foreign node (Rust)
gleamtk@127.0.0.1                   ui@127.0.0.1
  controller  ── {gui, Node} ! ──►  registered name: gui
  ◄── events ── {controller, …} ──  clicks / ready / pong

Protocol#

Gleam → UI ({gui, 'ui@127.0.0.1'} ! Term):

Term	Effect
`hello`	Handshake; UI records controller pid
`{set_title, Binary}`	Window title
`{set_label, Binary}`	Main label
`{set_count, Int}`	Counter display
`ping`	UI replies `pong`

UI → Gleam (to registered controller or the sender pid):

Term	Meaning
`{ready, <<"ui@…">>}`	UI node is up
`{clicked, Count}`	Primary button
`{count_changed, Count}`	− button
`pong`	Reply to `ping`
`window_closed`	Window closed

Requirements#

Nix (recommended) or: Erlang/OTP, Gleam, Rust, GTK4, libadwaita, epmd
A display (Wayland/X11) for the Relm4 window

Run#

cd gleamtk
nix develop          # or: nix develop -c bash
just run             # starts UI then Gleam controller

Two terminals:

# terminal 1
just ui

# terminal 2
just gleam

Click Click me / + in the window. Gleam prints events and updates the label and count over distribution.

Layout#

gleamtk/
  gleam/           # Gleam controller (BEAM node)
  ui/              # Relm4 + erl_dist foreign node
  justfile
  flake.nix

Notes#

Cookie defaults to gleamtk; both sides must match.
Long node names on 127.0.0.1 avoid short-name / hostname mismatches.
The Rust side uses erl_dist; the UI thread never blocks on distribution I/O.
This is a POC, not a full widget toolkit binding.

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