Haskell Real-Time Programming

Question

Being an insistent developer for several years, I never had a desire to learn functional programming.

A couple of months ago, I finally decided to learn Haskell. It's a pretty cool language, but I'm puzzled by how the event-driven application will be programmed in that language. Do you know a good tutorial about this?

Note: When I say "real application", I am not talking about the real world, but about the finished application. I just mean a small application for an example, just to understand it. I think something like a simplified version of the windows caculator would be great, and then maybe something more complicated.

Answer 1

When you give examples of the “real world”, you seem to think of problems that are essentially sequences or states or do a lot of I / O, right?

So what about games?

• Frag is a Quake clone implemented for undergraduate ( Functional Programming and 3D Games, Mun Hon Cheong, 2005 ). Here is a video in action .
• Super Monao Bros. (formerly known as Super Nario Bros.), well, maybe you can probably figure out which game is a clone from. ( This is an authoring English-language weblog. )
• Purely Functional Retrogames is a 4-part series of articles on how to write games in a purely functional language, explaining the use of Pacman as an example. ( part 2 , part 3 , part 4. )

Or, what about the X Window Manager , an extensible clone of Emacs text editor or IDE ?

Then there is a book in which even your question is already in the title: Real World Haskell and which is also available for free !

Another thing you can pay attention to is Functional reactive programming . (For example, it is used in Frag.) An interesting thing about FRP is that it allows you to look at a problem, say, graphical programming from a completely different angle. If you read the GUI chapter in the RWH book, you will see that it talks about how you can write a graphical application, like in C, only better. FRP OTOH allows you to write it in a completely different way, which is not even possible in C.

Many times (I’m not saying that this is the case in your question, but this is a repeating pattern) when someone says “but can Haskell be used in the real world”, what they actually say is “I know how to do it in C, and in Haskell I can't do it the exact same way, so it should be impossible in Haskell, so Haskell is not ready for the real world. But what they are missing out on is that there may be a completely different and much better way to solve the problem. (As if "Erlang has no threads, so it cannot be used to implement parallel systems.") And FRP is just one example.

Answer 2

For lightning-fast conversations, today I put together this list of Haskell applications with a show house, intentionally excluding everything that is only intended for programmers:

• darcs (35,000 locations since 2002): Distributed version control system with an innovative focus on state changes.
• xmonad (since 2007, 30,000 places): A well-known window tile manager with a huge layout library and other plugins. Made it a list, despite the fact that its configuration file was a Haskell file.
• hledger (since 2007, 9000 loc): text file based on a bi-directional accounting tool, ledger clone.
• Raincat (since 2008, 2000 loc): A platform game with a cat that does not want to get wet.
• arbtt (loc 2009, 2000): My rule-based automatic time tracking. Did it on the list like a shameless stub; probably not as popular. He now has a proper web page contributed by Waldir Pimenta.
• detexify (500 places since 2010): the back of the very useful LaTeX character finder is written in Haskell.
• git-annex (since 2010, 28,000 loc): manages your files and their location, a mix of Dropbox and git. Written by famous Joey Hess, who made a living from him through kickstarter. He is currently conducting a second round of financing !
• Nikki and Robots (since 2010, 18,000 loc): Platform game with Nikki and, well, his robots. it was released as a commercial independent game and sold through pay, something like a scheme, but the company unfortunately closed.
• hoodle (since 2011, 13,000 seats): A note and PDF annotation software, for example xournal .
• Chordify (from 2012 ?? loc): Music analyzes, for example. from a YouTube video and calculates the corresponding guitar chords. Closed software, but supposedly written in Haskell.

(Also featured on my blog , and on conversation slides , with good representative photographs of each program.)

Answer 3

xmonad is an event driven (literally). It has a listener loop that wakes up in events, changing the internal state that simulates the X server, which is then displayed on the screen.

http://xmonad.org

Answer 4

I once found this irc bot written in haskell:

http://www.haskell.org/haskellwiki/Roll_your_own_IRC_bot

Answer 5

Here are some links for your request.

This explains a lot of things that don't "make sense" to the imperative programmer about Haskell

Haskell Tutorial for C Programmers

This very nice, easy-to-use tutorial

Teach you Haskell for a great good

Raytracer written in Haskell

Haskell Raytracer

You can download the Glasgow Haskell compiler here. Ghc

Answer 6

You should check out Real World Haskell . The book is freely available and shows how Haskell can be applied to real problems. I would not call this a study tool, because it is much more comprehensive.

Answer 7

Note functional reactive programming .