Mathias Brandewinder on .NET, F#, VSTO and Excel development, and quantitative analysis / machine learning.
by Admin 24. August 2014 15:35

My recollection of how this all started is somewhat fuzzy at that point. I remember talking to @tomaspetricek about the recent “A pleasant round of golf” with @relentlessdev event in London. The idea of Code Golf is to write code that fits in as few characters as possible – a terrible idea in most cases, but an interesting one if you want to force your brain into unknown territory. Also, a very fun idea, with lots of possibilities. If I recall correctly, the discussion soon drifted to the conclusion that if you do it right (so to speak), your code should fit in a tweet. Tweet, or GTFO, as the kids would say (or so I hear).

Of course, I began obsessing about the idea, that’s what I do. The discussion kept going at LambdaJam, with @rickasaurus, @pblasucci and @bbqfrito (beers, too). So I thought I had to try it out: what if you set up a twitter bot, which would respond to your F# inquiries, and send back an evaluation of whatever F# expression you sent it?

As it turns out, it’s not that difficult to do, thanks to the fsharp Compiler Services, which lets you, among many things, host an FSI session. So without further due, I give you @fsibot. Tweet a valid expression to @fsibot, and it will run it in an F# interactive session, and reply with the result:

Note that you need to send an expression, as opposed to an interaction. As an example, printfn “Hello, world” won’t do anything, but sprintf “Hello, world” (which evaluates to a string) will.

What else is there to say?

A couple of things. First, my initial plan was to run this on an Azure worker role, which seemed to make a lot of sense. Turns out, after spending countless hours trying to figure out why it was working just great on my machine, using the Azure emulator, but exploding left and right the moment I deployed it in production, I just gave up, and changed track, rewriting it as a Windows Service hosted in an Azure virtual machine (it’s still a cloud-based architecture!), using the awesome TopShelf to simplify my life (thank you @phatboyg for saving my weekend, and @ReedCopsey for pointing me in the right direction).

You can find the whole code here on GitHub. As you might notice, the whole TopShelf part is in C# – nothing wrong with it, but I plan on moving this over to F# as soon as I can, using existing work by @henrikfeldt, who discreetly produces a lot of awesome code made in Sweden.

Another lesson learnt, which came by way of @panesofglass, was that if your code doesn’t do anything asynchronous, using async everywhere is probably not such a hot idea. Duh – but I recently got enamored with mailbox processors and async workflows, and started initially building a gigantic pipe factory, until Ryan aptly pointed out that this was rather counter-productive. So I simplified everything. Thanks for the input, Ryan!

That’s it! I am not entirely sure the bot will handle gracefully non-terminating expressions, but in traditional San Francisco fashion, I’ll call this a Minimum Viable Product, and just ship it – we can pivot later. Now have fun with it :) And if you have some comments, questions or suggestions, feel free to ping me on twitter as @brandewinder.

Source code on GitHub

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