A couple of months ago, Microsoft announced that they were buying a company called Xamarin, co-founded by the admirable Miguel “you can now flame me, I am full of love” de Icaza. (No sarcasm — I think Miguel is terrific, and the delightfully positive email linked above really stuck with me; if only I could have that attitude more often.)

As I understand it, Xamarin makes

1. the Mono runtime, a portable third-party implementation of Microsoft’s .NET runtime for the C# and F# programming languages
2. the eponymous Xamarin frameworks, which can be used with .NET to develop mobile apps for iOS and Android
3. plugins for the Visual Studio IDE on Windows and the MonoDevelop IDE on OS/X to support mobile platform builds using Xamarin (the MonoDevelop-plus-plugins combo is known as Xamarin Studio).

Then a couple of days ago, the newly-acquired Xamarin declared

1. that the Mono runtime was switching from LGPL/GPL licenses to MIT, allowing no-cost use in commercial applications
2. that Microsoft were providing a patent promise (which I have not closely read) to remove concerns for commercial users of Mono
3. that the Xamarin frameworks for iOS and Android, and the IDE plugins, were now free (of cost)
4. that at some future point the Xamarin frameworks would be open sourced

I’m trying to unpick exactly what this could mean to me.

According to this discussion on Hacker News, the IDE plugins are remaining proprietary (which appears to mean that no IDE on Linux will be supported, since the IDE plugins are not currently available for Linux) but that “the Xamarin runtime and all the commandline tools you need to build apps” will be open sourced.

What this means

as I understand it,

• Developers working on proprietary .NET applications will be able to build and release versions for other platforms than Windows, using Mono, at no extra cost
• Developers working on open source .NET applications will be able to publish the ensemble with Mono under the MIT license if desired and will (apparently) be free of patent concerns
• Developers will be able to make both proprietary and open source .NET applications for iOS and Android at no cost using Windows and OS/X
• There is a possibility of being able to do builds of the above using Linux as well once the SDK is open, though probably without an IDE

Unrelatedly, there are separate projects afoot to provide native code and to-Javascript compilers for .NET bytecode.

What I’m interested in

I do a range of programming including a mixture of signal-processing and UI work, and am interested in exploring comprehensible, straightforward functional languages in the ML family (I wrote a little post about that here). Unlike many audio developers I have relatively limited demands on real-time response, but everything I write really wants to be cross-platform, because I’ve got specialised users on pretty every common platform and I have limited time and funding. (I understand that cross-platform apps are often inferior to single-platform apps, but they’re better than no apps.)

Xamarin doesn’t quite meet my expectations because it’s not really a cross-platform framework in the manner of Qt (which I use) or JUCE (which is widely used by others in my field). Instead of providing a common “widget set” across all platforms, Xamarin provides a separate thin interface to the native UI logic for each platform. It’s hard to judge how much more work this is, without knowing where the abstraction boundaries lie, but it may be a more relevant and sensible distinction on mobile platforms (where the differences are often in interaction and layout) than desktops (where the differences are mostly about how large numbers of individual widgets look).

An ideal combination of language and framework for me goes something like

• strongly-typed, mostly functional, mostly immutable data structures
• efficient unboxed support for floating-point vector types, including SIMD support
• simple syntax (SML is nice)
• low-cost foreign-function interface for C integration
• high-level approach to multithreading
• can work with gross UI layout in HTML5 (possibly DOM-update reactive UI style?)
• good libraries for e.g. audio file I/O, signal processing, matrix algebra
• can develop on Linux and deploy to all of Linux, Windows, OS/X, iOS, Android
• free (or cheap, for proprietary apps) and open source (for open source apps)
• has indenting Emacs mode

Where F# appears to score

F#, Microsoft’s ML-derived functional language for the .NET CLR, hits several of these. It has the typing, mostly-functional style, syntax, FFI, multithreading, libraries, deployment and licensing, and potentially the development platform (if the open source Xamarin framework should lead to the ability to build mobile apps directly from Linux).

I’m not sure about floating-point and vectors or about reusable HTML-style UI. I’d like to make the time to do another comparison of some ML-family languages, focusing on DSP-style float activity and on threading. I’ve done a bit of related work in Standard ML, which I could use as a basis for comparison.

Unless and until I get to do that, I’d love to hear any thoughts about F# as a general-purpose DSP-and-UI language, for a developer whose home platform is Linux.

My impression from the feedback on my earlier post was that the F# community is both enthusiastic and polite, and I notice that F# is the third most-loved language in the StackOverflow’s 2016 survey. Imagine a language that is useful no matter what platform you’re targeting, and whose developers love it. I can hope.