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Functional Languages Under .NET/CLR
Numen writes "With all the talk of .NET being thrown about there is a common factor occuring through many discussions, namely the claim that .NET will be unable to address functional and logic languages such as Prolog and LISP.
To this end I would like to drawn peoples' attention to two resources, that shown how this may well be a non-issue, and to ask, does this change anybodies mind?
"
Does anyone know how .NET does for speed?
.NET introduce an even bigger overhead, or have they sorted it out?
.NET instead? Will the tailor-made version be more efficient because it's designed with the language in mind, or does the benefit of having all the optimisations done on a common system compensate for that?
ie, Java takes an absolute age to initialise which makes it unsuitable for desktop applications or utilities (although people still try... maybe in a few years' time...).
Does
Also, is there any overhead for languages that aleady use a VM (eg, python, perl) if they switch to
I really like the idea of a common cross-platform runtime, but not if it makes my text editor take 5 seconds to load!
I wonder where we would be if Microsoft had enbraced (but not extended) Java, such that both Sun and MS had meanful discussions on how to expand it and yet keep the promise of "Write Once, Run Everywhere" (ie, no MS-specific extensions, and so forth). The idea that any vendor could release code that would run on 100% of the computers out there, not just 95%, would be a godsend.
While .NET, and efforts by Miguel and Ximian to create Mono, and probably similar efforts inhouse at Apple, appear to offer the same promise, I still expect that we'll see a lot of Windows-specific hooks that would prevent a good chunk of code of being cross compatible. Not that one can't write fully compatiable .NET code that runs everywhere, but I would not be surprised if MS offered programming goodies (cool widgets, eyecandy features, etc) that would be easily be limited to Winboxen and leave other implimentations of the virtual machine out in the cold.
"Pinky, you've left the lens cap of your mind on again." - P&TB
"I can see my house from here!" - ST:
Why? One major advantage of functional programming languages for optimization is that the compiler knows that almost nothing can change behind its back: variables can't get updated, data structures can't get changed, etc. With VLIW architectures like Itanium and hyperthreading, functional programming languages can potentially do much better relative to traditional languages than on older processors. But in order to so so, their compilers need a degree of control over code generation that simply isn't available if you go through CLR or JVM.
Furthermore, the entire runtime of a functional language is optimized for the kinds of allocation patterns that come along with functional programming, while CLR and JVM are optimized for OOP. For lazy functional languages, there are some additional issues when it comes to expressing lazy evaluation efficiently.
Altogether, though, I think it really doesn't matter. CLR and JVM are good and fairly flexible platforms, but platform evolution won't stop here. If anything, Sun is a bit more honest in this regard, making no bones about the fact that JVM is primarily a Java platform, even though there are dozens of other language frontends available for it; CLR claims universality, but really isn't any better than JVM.
If you don't care that much about performance, you can use your functional language under CLR and JVM. If you want a high-performance functional programming language, you can use one of the dedicated native code compilers and runtimes that will continue to be available. CLR and JVM will not end the evolution of other runtimes.
I took a look around and found this link to a guy called Don Syme at Microsoft Research who appears to be working on just this.
There's also the Mondrian project, which implements Haskell.
What do you mean about "windows-only" hooks???
.NET is. Let me set the record straight: the functionality... the "API"... of .NET is contained in the core class libraries. Those are PUBLICLY AVAILABLE INTERFACES. There is nowhere to "HIDE" windows-only hooks. If you can have your MONO class library take CallX with four arguments of int just like the MS Windows version of the class, then you have CROSS PLATFORM capability. If Microsoft changes the class interface, then you change your corresponding class interface.
I am constantly amazed at the complete LACK of understanding about what
Honestly! It's all Object Oriented; there is NOWHERE to hide anything from anyone! Implementation is another issue, but by virtue of the platform itself all the interfaces have to be public and accessible, which means they can be easily emulated. That's what mono is trying to do with WindowsForms; its the GUI component that Microsoft said was going to be Windows-only, except they are already working on emulating the public interfaces (though the implementation would be calling gtk/x)
Please... THINK about this stuff before you post it. Its no like Sun can go and hide some new solaris-only hooks in the JVM that suddenly make it incompatible with other platforms! In order to have developers use the new hooks, they have to make them public, and then anyone could create a compatible class for their platform of choice.
Natural != (nontoxic || beneficial)
Okay, I apoligize for an extra long post here, but I still see people mischaracterizing functional programming. So I'm going to take a few excerpts from "Why Functional Programming Matters" by John Hughes. It's a short paper, worth your time if you're new to the functional paradigm.
No Side Effects:
Functional programs contain no side-effects at all. A function call can have no effect other than to compute its result. This eliminates a major source of bugs, and also makes the order of execution irrelevant - since no side-effect can change the value of an expression, it can be evaluated at any time. This relieves the programmer of the burden of prescribing the flow of control. Since expressions can be evaluated at any time, one can freely replace variables by their values and vice versa - that is, programs are "referentially transparent". This freedom helps make functional programs more tractable mathematically than their conventional counterparts.
Higher Order Functions:
Functional languages allow functions which are indivisible in conventional programming languages to be expressed as a combi-nation of parts - a general higher order function and some particular specialising functions. Once defined, such higher order functions allow many operations to be programmed very easily. Whenever a new datatype is defined higher order functions should be written for processing it. This makes manipulating the datatype easy, and also localises knowledge about the details of its represen-tation. The best analogy with conventional programming is with extensible languages - it is as though the programming language can be extended with new control structures whenever desired.
Lazy Evaluation:
A complete functional program is just a function from its input to its output. If f and g are such programs, then (g . f ) is a program which, when applied to its input, computes g (f input). The program f computes its output which is used as the input to program g. This might be implemented conventionally by storing the output from f in a temporary file. The problem with this is that the temporary file might occupy so much memory that it is impractical to glue the programs together in this way. Functional languages provide a solution to this problem. The two programs f and g are run together in strict synchronisation. F is only started once g tries to read some input, and only runs for long enough to deliver the output g is trying to read. Then f is suspended and g is run until it tries to read another input. As an added bonus, if g terminates without reading all of f 's output then f is aborted. F can even be a non-terminating program, producing an infinite amount of output, since it will be terminated forcibly as soon as g is finished. This allows termination conditions to be separated from loop bodies - a powerful modularisation. Since this method of evaluation runs f as little as possible, it is called "lazy evaluation". It makes it practical to modularise a program as a generator which constructs a large number of possible answers, and a selector which chooses the appropriate one. While some other systems allow programs to be run together in this manner, only functional languages use lazy evaluation uniformly for every function call, allowing any part of a program to be modularised in this way. Lazy evaluation is perhaps the most powerful tool for modularisation in the functional programmer's repertoire.
Why you might care:
Modularity is the key to successful programming. Languages which aim to improve productivity must support modular programming well. But new scope rules and mechanisms for separate compilation are not enough - modularity means more than modules. Our ability to decompose a problem into parts depends directly on our ability to glue solutions together. To assist modular programming, a language must provide good glue. Functional programming languages provide two new kinds of glue - higher-order functions and lazy evaluation. Using these glues one can modularise programs in new and exciting ways... Smaller and more general modules can be re-used more widely, easing subsequent programming. This explains why functional programs are so much smaller and easier to write than conventional ones. It also provides a target for functional programmers to aim at. If any part of a program is messy or complicated, the programmer should attempt to modularise it and to generalise the parts. He should expect to use higher-order functions and lazy evaluation as his tools for doing this.