Friday, July 09, 2010 1:42 PM
F# Discoveries this Week 07/09/2010
This week we once again reap another huge crop of fantastic F# content. In fact, it’s been getting so overwhelming that I’ll be moving to an every week format from here on out. Please come in, read, and enjoy!
With its new tools, the bank can speed development by 50 percent or more, improve quality, and reduce costs.
The next meetup of the F#unctional London Meetup Group will be held on July 28, with Zach Bray talking on Agile Acceptance Testing with F#
I met Syme at the QCon conference in London, in March 2010, and interviewed him shortly afterwards. Some quotes from that interviewed have already been published in an article for The Register, but I am now posting nearly all of it here.
Thanks to everyone on twitter who voted!
Quantifa is an F# open-source library for quantitative finance and risk management.
The F# mode for Emacs is two years old, and has been downloaded more than 1,000 times.
Tabbles is a new way of organizing files: it combines virtual folders and tags, and auto-organizes and tags your files in very intelligent ways.
Audio / Video
In earlier versions of the billing system, much of the business logic resided in SQL Server and various Perl and Java programs. That made the solution hard to maintain and tailor to the needs of the customers. By using F# instead of an object oriented language the developers at Svea Ekonomi can be a lot more productive.
I’m a sucker for eye-candy, and the other day I came across the beautifully lit renders produced by Minilight. It’s a nice, minimal implementation of a global illumination renderer that’s been ported to a wide variety of different languages from C to ActionScript. So of course, I couldn’t resist trying to implement it in F#.
Another example from Sal Mangano's Mathematica Cookbook, this time taken from Andreas Lauschke's example, is a "fast" pricer for American options. The relevant section of the book stresses the importance of performance in this context and the Mathematica code presented was heavily optimized by experts.
Another example from Sal Mangano's Mathematica Cookbook (p.520) is an elegant little Mathematica program that uses a crude numerical integrator to plot the trajectory of a differential equation representing the populations of predators (foxes) and prey (rabbits):
The simpler F# solution is also 20× faster at inserting 100k elements and 100× faster at computing the range of depths in the resulting tree.
The Lorenz attractor is a fractal derived from the trajectory of a 3-dimensional dynamical system that exhibits chaotic flow. This blog post describes a 35-line program that computes trajectories of this attractor and visualizes them as a beautiful whisp using Windows Presentation Foundation.
Even before I started experimenting, I realized that checking a list for sorting was just a specific example of checking whether the pairs in a list satisfied a certain binary order relation. So I decided to work directly on a more general solution.
Learning to construct continuations can be tough. It’s easy to state how they work: they facilitate tail recursion by recursively passing the remainder of a computation. But it can be a lot harder to actually get one working from scratch.
Without further ado, here is my first F# implementation of Dijkstra’s shunting-yard algorithm, including a basic test (based on the example at Wikipedia). This is probably not a minimal or most-efficient implementation, but it is a starting place.
While working on an internal domain-specific language, I encountered a case where passing a unit into a function made the syntax somewhat more readable. The completely artificial example below illustrates the concept as the function xfer1. I also tried a two-unit version, which is illustrated as xfer2.
Thanks to all who come out to the New England F# User Group meeting tonight!
If you ever tried to call a SQL stored procedure directly using the SqlCommand, then you can surely appreciate the elegance of this code snippet. Let's now take a look at a larger example and some of the neat tricks that make this possible...
After looking at skew heap, merge sort and Cartesian tree, I figured there has to be a way to combine all three.
Last time, we created a library of Search Engine Optimization (SEO) helpers. This time we’ll see how to use them to actually fetch information about your webiste rankings (and your competitors’).
Every day, the European Central Bank publishes “official” reference FX (foreign exchange) rates where currencies are quoted against the Euro (expressed as EUR/XXX), or 1 EUR = xxx XXX. The exchange rates of the last thirty sessions are available in xml format which we shall try to parse. In order to do so, we use F# and active patterns, based on Don Syme’s draft paper.
That said, this post will take you through my solution for Euler 54, which (somewhat unusually) isn't a particularly mathematical problem, but turns out to be a great way to demonstrate some of the features of the F# language. The basic principle of this problem is to compare two hands of cards in the game of poker, and to determine which is the winning hand.
Those of you who are doing Project Euler know what I am talking about by the EulerMaths library. There are certain fundamentals which crop up again and again in the questions and it is important to work these into a reusable and performant library.
As an advocate for using the right tool for the job, I have created a new WPF MVVM multi-project template composed of an C# View project, an F# ViewModel project, and an F# Model project.
This is a very simple Eliza like chat bot. I call it Meliza Sharp. I wrote it for having fun learning the F# language shipped with Visual Studio 2010.
Pretty cool, huh? This trick can be used for other things, since PrintfFormatProc is fully reusable. For example, I'm currently using PrintfFormat manipulation to define type-safe routing in a web application
Today I was doing some work work and kept having to parse a log file. After a few hours of doing the same routine stuff I thought I might try and automate it using F#.
Mads Kristensen has a nice post where he shows how to read stock quotes from Yahoo finance using C#, which was very helpful to get started. I figured it would be interesting to try out a conversion to F# and see what the result looked like.