Nim for Haiku

Write native Haiku GUI applications in Nim instead of C++. Your app code is pure Nim; a small, reusable C++ shim bridges to Haiku's native API.

The app above is src/app.nim — about 15 lines of Nim, packaged as a native .hpkg and shown in the Deskbar. No C++ in the app itself.

Why this exists

Haiku's application framework (the BeAPI) is C++, and its GUI model is built on subclassing: you extend BWindow or BView and override virtual methods. Nim's C++ backend can call the BeAPI directly, but it can't emit a native C++ subclass with overridden virtuals — that one gap is the whole reason a C++ layer is needed at all.

The answer is a thin, generic shim that subclasses the BeAPI once and forwards every event to a Nim callback. You write Nim; the shim is fixed library plumbing you never touch. This is the same shape every high-level language uses to bind a C++ framework.

How it works

The click path shows both directions of the bridge:

• Nim to BeAPI — Nim owns main and calls the shim to build the window.
• BeAPI to Nim — a button click routes through the shim into a Nim closure.

Buttons target the application object, so click handlers run on the app thread, where Nim's garbage collector and closures are safe. When a handler updates a view, the shim locks that view's window first, as the BeAPI requires.

Repository layout

| Path | What it is | | --- | --- | | src/app.nim | The example app, in pure Nim. Start here. | | src/haiku.nim | The high-level Nim API. Add a widget here when you need one. | | src/haiku_shim.cpp | The generic C++ binding. Write-once; you don't edit it. | | src/gui.nim, src/gui_shim.cpp | Minimal annotated demo of the shim pattern. | | packaging/ | Package metadata (PackageInfo, app signature .rdef). | | ship.sh, test-gui.sh, ship-pkg.sh | Build-and-run and packaging scripts. | | JOURNAL.md | How the spike went, including every gotcha and its fix. |

Requirements

• A Haiku machine (tested on R1/beta6, x86_64) reachable over SSH as haiku. Install the toolchain there with pkgman install nim rsync.
• Nim and rsync locally, for editing and fast type-checking. devbox shell provides both.

Development happens on Linux; the code builds and runs on Haiku over SSH. See CLAUDE.md for the SSH setup (Haiku's user account is root, and it reads authorised keys from ~/config/settings/ssh/authorized_keys).

Build and run

Check the Nim locally without linking:

devbox run check

Build and run a target on Haiku (source syncs over, compiles, and runs there):

./ship.sh hello        # a plain CLI program
./test-gui.sh          # the GUI demo — also screenshots the window

Ship a package

Build an installable Haiku package:

./ship-pkg.sh          # -> dist/counter-<version>-x86_64.hpkg

To install, copy the .hpkg into /boot/system/packages/ on the Haiku machine; packagefs activates it and the app appears in the Deskbar. To ship an update, bump version in packaging/PackageInfo — packagefs ignores a rebuild that keeps the same version.

Status

A viability spike, and the verdict is yes: Nim is a workable higher-level language for Haiku apps, app code stays pure Nim, and the result ships as a normal package. JOURNAL.md has the full story.

Licence

MIT.