Code included here is over simplified for clarity, I hosted a better implementation code on CodePlex. These modifications change strictly nothing for the client code and are only an implementation detail. I use a continuation rather than a delay, and I chose to design a custom continuation class rather than using a delegate because of a type system limitations.
Most GUI frameworks, including Silverlight and WPF, are shipped with a fundamental problem: long use of the main thread causes the Window to blackout, and using different threads requires you to get your hands dirty with the Dispatcher stuff and freezable objects. Worse, you wont learn the necessity to do so until you get a surprise of “The calling thread cannot access this object because a different thread owns it.” exception when all what you were doing is to use available methods on an object that seemed you have access to, at lease it seemed until runtime! This post illustrates a solution based on Monads abstraction and LinQ syntax.
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Jim Webber from http://www.infoq.com/interviews/robinson-webber-rest 00:37:08:
We did put abstraction after abstraction onto our distributed system infrastructure and you know what: it hasn’t worked out that well for us. Some of the largest and most sophisticated distributed systems on the planet haven’t been all that large or sophisticated and then this kind of crappy protocol comes along that insists on being synchronous, and insists on being text-driven and it scales globally. That’s shocking and does not make sense to us as engineers. That’s the web paradox - it’s the rubbishest thing on the planet, but it scaled and for me that is what’s hit the reset button because I was totally up for XML-based protocols that do all sorts of funky stuff.
Those that follow my twitter @sadache , me @infoQ or my blog have certainly already noticed that I am quite interested in Scala on languages’ axis and in Domain Context Interaction DCI pattern on architecture axis. I always search new ways for delivering quality code which is modular and concise. Modularity offers the opportunity to think about the problem in parts, which is typical of the way brains work, whereas conciseness makes use of imaginary system (reading code blocks like images).
Recently, I’ve been working on a Web Api system where, thanks to support of @jeanlaurent http://morlhon.net/blog/, I used Scala applying DCI architecture in a real world project. This post is about reporting benefits of using this approach. Other posts will follow that will be more focused on the use of Scala and Functional Programming in that project. Code included is a bit simplified and parts of the system that are not of interest are omitted.
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from Rich Hickey on Clojure’s Features and Implementation
Clojure multimethods are just another level of that same logic, in fact they are a realization of the last sentence I just said. They are dispatch based upon an arbitrary function of the arguments. You define a multimethod and you say “Here is a function of the arguments I’d like you to use” You could look at the first argument, you could look at the 5th, you could look at all of them, you could look inside them, some member of an argument, it could look at the types or not or the values. Now, you could look at relationships between arguments, you have dispatch based upon an arbitrary function of the arguments and you have a vastly wider set of polymorphic possibilities than you had before and it’s quite powerful. In particular, it allows you to do Runtime dispatch on Runtime attributes. You don’t usually represent something like being hungry as part of something’s type, it’s some attribute that it acquires while the program is running or being outdated or things like that. Now you can access those things and you can do things polymorphically based upon that and take a lot of switch statements out of your code.
Should I call it first class Pattern Matching? or Pattern Matching in disguise?
An interview I did with Paul Hudak that begins with a discussion of when to introduce difficult Haskell concepts like monads, moves to a discussion of the philosophy of higher order programming, the success and influence of Haskell, its use in the mainstream, and concludes with the idea of teaching computer music and Haskell simultaneously.
http://www.infoq.com/interviews/paul-hudak-haskell-Qcon-SF-08&language=en
James O. Coplien and Trygve Reenskaug have recently introduced a new architectural approach to OOP based on Data, Context and Interaction pattern. It should allow capturing user mental model in terms of behavioral requirements, something that classic OOP fails to do. The article, that triggered many reactions and critics, provides insights into DCI using concrete examples to show its advantages.
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From my QCon09 London presentation slides.
LinQ is often understood in terms of introducing a Domain Specific Language to work with data to C# and .Net in general. The fact is:it is not, and there is a considerable difference between LinQ syntax nature and a DSL. The problem is that DSL definition is blur enough to take anything interesting or cool under it!
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Most GUI frameworks, including Silverlight and WPF, are shipped with a fundamental problem: long use of the main thread causes the Window to blackout, and using different threads requires you to get your hands dirty with the Dispatcher stuff and freezable objects. Worse, you wont learn the necessity to do so until you get a surprise of “The calling thread cannot access this object because a different thread owns it.” exception when all what you were doing is to use available methods on an object that seemed you have access to, at lease it seemed until runtime! This post illustrates a solution based on Monads abstraction and LinQ syntax.
