Programming user interfaces using F# workflows
Numerous Manning partners already published several exceprts from my Real-World Functional Programming book. You can find a list on the book's web page. However, the last excerpt published at DotNetSlackers is particularly interesting. It discusses how to use F# asynchronous workflows to write GUI applications. This is a very powerful programming pattern that is very difficult to do in any other .NET language. We first discussed it with Don Syme during my internship at Microsoft Research and I found it very elegant, so I made some space for it in the book. In fact, the entire Chapter 16 discusses various reactive programming techniques that can be used in F#.
When designing applications that don't react to external events, you have lots of control flow constructs available, such as if-then-else expressions, for loops and while loops in imperative languages, or recursion and higher-order functions in functional languages. Constructs like this make it easy to describe what the application does. The control flow is clearly visible in the source code, so drawing a flowchart to describe it is straightforward.
Understanding reactive applications is much more difficult. A typical C# application or GUI control that needs to react to multiple events usually involves mutable state. When an event occurs, it updates the state and may run more code in response to the event, depending on the current state. This architecture makes it quite difficult to understand the potential states of the application and the transitions between them. Using asynchronous workflows, we can write the code in a way that makes the control flow of the application visible even for reactive applications.
You can read the complete article here: Programming user interfaces using F# workflows [^]. It is also worth adding that Manning offers 30% discount to DotNetSlackers readers (see the article for details!)
Permanent link & comments (English)
Thursday, February 18, 2010
Using custom grouping operators in LINQ
You can use LINQ to write queries that perform grouping of data using group by
or ordering of data using orderby clause. LINQ provides the default
(and the most common) implementation of both of the operations, but sometimes you
may need a slightly different behavior when grouping or ordering data (this article
is motivated by a question on StackOverflow
which needs to do exactly that for grouping).
Let's look at a simple example, which shows when we may need a different behavior when
grouping data. For example, we may have the following list of stock trades
containing a name of a stock and the price of the trade (stored for example as a list
of TradeInfo classes with properties Name and Price):
{ { Name = "MSFT", Price = 80.00 },
{ Name = "MSFT", Price = 70.00 },
{ Name = "GOOG", Price = 100.00 },
{ Name = "GOOG", Price = 200.00 },
{ Name = "GOOG", Price = 300.00 },
{ Name = "MSFT", Price = 30.00 },
{ Name = "MSFT", Price = 20.00 } }
Now, we may want to group adjacent trades into a single summary record which will contain the name of the stock (which is same for all trades in each group), the number of trades in the group and an average price in the group. The desired results are:
{ { Name = "MSFT", Count = 2, AvgPrice = 75.00 },
{ Name = "GOOG", Count = 3, AvgPrice = 200.00 },
{ Name = "MSFT", Count = 2, AvgPrice = 25.00 } }
The operation that we want to do is very similar to group by in LINQ, but
it doesn't do quite the same thing! If we used group by, we would get only
two groups as the result. However, as I wrote earlier, we want to group only
adjacent trades. You could write your own extension method to do this,
but then you need to leave the elegant LINQ query syntax. In this article, I'll show
you how to get the desired results using a simple LINQ query with a group by
clause...
Read the complete article (English)
Sunday, February 07, 2010
Deal of the day: Real-World Functional Programming
Some time ago, I received my copies of Real-World Functional Programming. I started working on it back in May 2008 and as many people who had more experience with writing books told me, it took longer than I was expecting! Anyway, I have to say, it was worth it, holding the actual printed book with my name on the cover is just fantastic!
The goal of the book is to present functional programming concepts and ideas in a readable form. I wanted to create a book that will teach you how to think functionally without using the usual shock therapy that people usually feel when seeing functional programming for the first time. There are already a couple of reviews that suggest I was quite successful:
- Functional Programming for the Real World, by Tomas Petricek and Jon Skeet, has been a very helpful book for moving to F# from C#, as the authors do a fantastic job of helping to explain the differences between OOP and FP.
James Black at Amazon.com - This book isn’t just a simple introduction to programming in F#; it’s an introductory text on functional programming covering the many reasons why it is time for this programming paradigm to finally be accepted by mainstream programmers. And it also contains much more...
CliveT, Software Engineer at Red Gate Software - ... and there are many other great comments about the book at Manning book page.
Deal of the day (January 24)
Finally, here is one great news if you're interested in getting the book! Real-World Functional Programming is Manning's Deal of the Day this Sunday, January 24. On this day, the print book is available for $20 from the Manning website, with code dotd0124.
Read the complete article (English)
Sunday, January 24, 2010
Accelerator and F# (IV.): Composing computations with quotations
In this article series, we're talking about the Accelerator project and I'm
presenting an F# library that I implemented, which allows you to use Accelerator [references]
in a more sophisticated way. We've seen two examples of using Accelerator directly
(see also introduction and Game of Life).
In the previous article
I introduced my F# library for working with Accelerator. We've seen F# functions from the
DataParallel module, we implemented an algorithm that rotates an image
using these functions and finally, we've seen that we can take this ordinary F# code
and run it using Accelerator. This is all possible thanks to F# quotations, which
we can use to get an AST (a source code) of an F# function we wrote (if the function
is marked in some special way).
In this part of the series, we're going to look at working with quotations explicitly. We'll use meta-programming techniques to work with Accelerator. Meta-programming means writing programs that manipulate with other programs or pieces of code. This is exactly what we're going to do in this article. We'll write an F# function (running on CPU) that builds a program, which we'll then run using Accelerator.
This is quite interesting approach, which isn't possible when we call Accelerator methods as standard F# functions or .NET methods. The benefit is that we'll clearly see which parts of program run on CPU and what parts execute on GPU or using X64 multi-core target. We could also perform more complicated optimizations with the code (because this wouldn't affect the readability). Just for your reference, here is the list of articles in this series in case you missed some of them:
- Accelerator and F# (I.): Introduction and calculating PI
- Accelerator and F# (II.): The Game of Life on GPU
- Accelerator and F# (III.): Data-parallel programs using F# quotations
- Accelerator and F# (IV.): Composing computations with quotations
However, enough with theory and let's take a look at some code samples! This time, we'll implement blurring of an image (also called convolution). Another example how to write this in F# using Accelerator is Satnam Singh's blog post [4]. Our example will be different, because we'll write the code as standard F# program and then have it translated to Accelerator automatically using quotations. We'll also talk about the architecture of the library that we're using and look at some performance results.
Read the complete article (English)
Tuesday, January 12, 2010
Accelerator and F# (III.): Data-parallel programs using F# quotations
If you've been following this article series, you already know that Accelerator is a MSR library [1, 2] that allows you to run code in parallel on either multi-core CPU or using shaders on GPU (see introduction). We also discussed a direct way to use Accelerator from F# (by calling Accelerator methods directly) and implemented Conway's Game of Life. In this article, we'll look at more sophisticated way of using Accelerator from F#. We'll introduce F# quotations and look at translating 'normal' F# code to use Accelerator.
In general, F# quotations allow us to treat F# code as data structure and manipulate with it. This is very similar to C# expression trees, but the F# implementation is more powerful. We can also mark a standard method or a function with a special attribute that tells the compiler to store quotation of the body. Then we can access the quotation and traverse it or modify it. In this article we'll use a function that takes an F# quotation (containing a limited set of functions) and executes it using MSR Accelerator. Implementing this functionality is a bit complicated, so we won't discuss the implementation now. We'll leave this for some future article of this series. In future, we'll also look at other interesting possibilities that we have when writing code using quotations. Here is a list of articles in this series and of the articles that I'm planning to add:
- Accelerator and F# (I.): Introduction and calculating PI
- Accelerator and F# (II.): The Game of Life on GPU
- Accelerator and F# (III.): Data-parallel programs using F# quotations
- Accelerator and F# (IV.): Composing computations with quotations
Read the complete article (English)
Monday, January 04, 2010
Accelerator and F# (II.): The Game of Life on GPU
In the previous article, I introduced the Microsoft Research Accelerator library. It allows us to write computations with arrays in C# and execute them in parallel on multi-core CPU or more interestingly, using GPU shaders. In the previous artcile, we've seen how Accelerator works and how it can be accessed from F#. In this article, we'll look at one more interesting F# demo - we'll implement the famous Conway's Game of Life [1] using Accelerator. We'll use a v2 version of Accelerator which has been announced just recently and is available from Microsoft Connect [2].
This article is the second one from a series about using Accelerator from F#. Today, we'll use Accelerator types directly from F# - this is the simplest possible approach and is very similar to the way you'd work with Accelerator in C#. However, we can use some nice F# features such as custom operators to make the code more readable. In the next article, we'll discuss a different approach - we'll look how to execute more "standard" F# code (that doesn't reference Accelerator explicitly) with Accelerator using F# quotations. The list of articles may change, but here is a list of articles that I'm currently planning to write:
- Accelerator and F# (I.): Introduction and calculating PI
- Accelerator and F# (II.): The Game of Life on GPU
- Accelerator and F# (III.): Data-parallel programs using F# quotations
- Accelerator and F# (IV.): Composing computations with quotations
Read the complete article (English)
Monday, December 28, 2009
Accelerator and F# (I.): Introduction and calculating PI
I already wrote about two projects that I worked on during an internship at MSR back in 2007 (ASP.NET support in F# and F# WebTools). Even though this was more than 2 years ago (and I did one more internship at MSR in the meantime), I still have one more project that I never published on the web. The folks from the F# team reminded me of this project recently, so I thought I could finally publish it. The project used Microsoft Research Accelerator [1, 2], which is a C# library for developing array-based computations and executing them on a GPU. More recently, the Accelerator team at MSR published Accelerator v2 [3], which was a good motivation to update my original project...
In this article, we'll look at the simplest way of using Accelerator from F#. Accelerator provides a managed interface that can be naturally used from both C# and F#. We can use a mix of method calls and overloaded operators to describe a computation. In F#, we'll also define our additional custom operators to make the code a bit nicer. After we introduce Accelerator using a simple C# demo, we'll look how to calculate an approximate value of the PI number using a Monte-Carlo method.
This article is the first one from a series about using Accelerator from F#. The list of articles may change, but here is a list of articles that I'm currently planning to write:
- Accelerator and F# (I.): Introduction and calculating PI
- Accelerator and F# (II.): The Game of Life on GPU
- Accelerator and F# (III.): Data-parallel programs using F# quotations
- Accelerator and F# (IV.): Composing computations with quotations
Read the complete article (English)
Monday, December 21, 2009
Real-World Functional Programming: Completed and printed!
If you're following my blog or if you're interested in F# or functional programming in .NET, you probably noticed that I was working on a book Real-World Functional Programming. At some point, we called it Functional Programming for the Real-World, but then we changed the title back to a better sounding version Real-World Functional Programming (subtitle With examples in F# and C#). The book is also reason for a lower number of blog posts over the last year. Over the last month or so, we were doing the final edits, reviewing the final PDF version (I fixed quite a lot minor issues, synchronized book with the Beta 2 F# release and so on). Anyway, before a few days, I received the following email (as an author, I receive the same emails as those who ordered the book through the Manning Early Access Program, so that I can see what we're sending to our dear readers):
|
Dear Tomas Petricek, |
Finally finished!
Yes, that's right. The book is finally completed and as far as I know, it has been printed last week! If you already ordered the book, you won't receive it before Christmas, but it should come shortly after. I can't wait to see the book actually printed. The transition from the Word drafts I initially wrote to a final PDF version was already felt fantastic and I thought "It looks like a real book!" Among other things, there are now graphical arrows with comments inside listings, which looks really great and makes code listings much easier to read. Now I can look forward to seeing the actual book. Maybe I'm too conservative, but I have to say that I'm really glad that I wrote the book before everything is going to be published just electronically!
Here is a couple of links that you may found interesting if you want to look inside the book...
Read the complete article (English)
Saturday, December 19, 2009
Functional Programming: Available Chapter Excerpts & Discount
The work on my book Functional Programming for the Real World is slowly getting to the end. I'm currently creating index for the last couple of chapters and doing final updates based on the feedback from reviews and also from the forum at manning.com (this means that if you have some suggestions, it's the best time to post them - I haven't yet replied to all of them, but I'll certainly do that before the manuscript will go to the production).
Read the complete article (English)
Sunday, July 26, 2009
F# Webcast (IV.) - Developing standard .NET libraries
In the previous parts of this webcast series we've developed an F# script that downloads RSS feeds
asynchronously and in parallel and searches them for the specified keywords. We followed the usual F#
development style, so after introducing the basic functional
concepts, we wrote the code in the simples possible style
and demonstrated how to use System.Xml and System.Net namespaces. Then we
refactored the existing code, to run asynchronously and process
the results potentially in parallel, which was very easy thanks to F# asynchronous workflows.
In this part of the series, we'll make the next evolutionary step of our sample application. We'll turn the code that originally used F# tuples and lists into code that uses standard .NET objects and we'll also see how to declare a class in F#. This simple modification will turn the script into an F# library that is almost indistinguishable from a library developed in C#. We'll also look how you can use the library from C# web application to show the interop between C# and F# in practice. We'll start with the code from the previous part, so if you missed that, you may want to check it out or download the source code.
Read the complete article (English)
Monday, June 15, 2009