Haskell desktop GUIs with bindings-cef3

While web technologies and apps “in the cloud” are easily the dominant trend in application programming these days, there are still some situations in which reliable old desktop apps are superior. For example, most of my experience is in the defense industry, and there is no way the cloud would get trusted with sensitive files without appropriate protections. So how can we leverage the efforts and progress of web interface programming on the desktop, especially with regard to Haskell?

One option that I have some experience with is threepenny-gui, which uses the web browser as an interface to a Haskell backend server that runs locally (or over a LAN – really any low latency situation). An early version of threepenny is used in FNIStash. While effective, something just feels wrong to me about running desktop applications inside a browser application. Really what I’d like to do is incorporate browser functionality inside my applications instead of relying on Google, Mozilla, or even Microsoft.

Enter the Chromium Embedded Framework. It’s a fully functioning, bare-bones browser and javascript engine packed inside a .dll or .so file. Add some tabs, a URL bar, bookmarks, etc, and you have a modern browser. Alternatively, you can use CEF to provide HTML and JS driven GUIs for desktop applications. Indeed, the Steam client does this very thing! Adobe uses it as well. In fact, it’s pretty popular.

CEF provides a C API, which we can call from Haskell with appropriate bindings. I cut my teeth recently with the bindings-dsl by defining the bindings to the low level interface of the HDF5 library. Bindings to the CEF library seemed like a good follow on activity, especially since I’d like to use it in my own Haskell projects.

So I created bindings-cef3, Haskell bindings for the CEF3 C API. The package includes an optional example program that creates a browser window and loads a URL. There’s a snapshot below. These bindings are very low level, so there is ample opportunity to wrap them in a smarter, more convenient Haskell API. This is something I plan to do myself eventually, unless a more experienced Haskeller beats me to it!

Beware that because of the multiple interdependent types in CEF3, nearly all of the bindings are provided in a single file. It can take a while to preprocess and compile. When I was working on it, I had up up the RAM on my virtual machine from 4 GB to around 5 GB to avoid cryptic gcc errors. If anyone knows a better way to structure the library to avoid these hurdles, I’d love to hear it.

The library is not currently on Hackage as of this writing, and that is intentional. The current version only supports Linux, and being an occasional Windows Haskell developer myself, I don’t like the idea of keeping out Windows (and MacOS) users. Only a little more coding effort and a decent amount of testing effort is required for other platforms, and I welcome contributions from anyone wanting to help. Once it has been vetted a little more and better compatibility is implemented, joining Hackage with other bindings library seems only natural.

While bindings to CEF3 is just a first step toward having “true” Haskell desktop GUIs driven by web technologies, it’s an important step. More experimentation is needed to uncover quirks and limitations; I’m certainly no CEF expert. In fact, I probably know only as much as is necessary to get the example application working 🙂 . Hopefully this library will help out anyone frustrated with Haskell GUIs like I have been before!

Screenshot of cefcapi example program.

]8 Screenshot of cefcapi example program.