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I plan on writing webapps with Snap.
But sticking with snap-core is much more straightforward to me than using snaplets and lenses.
Is it maintainable in the long-run to start developing with snap init barebones and then adding heist templates, HDBC database persistence, etc by hand, without resorting to the Lens stuff? How strongly is the Snap core team encouraging the use of Snaplets in addition to snap-core in practice?
As ocharles said, you can certainly build large web apps in snap-core without using snaplets. However, snaplets were developed directly from our experience with real world apps. We observed that we ended up writing a lot of the same boilerplate all the time. For almost any sufficiently complicated application we found that you'll usually want at least a reader and/or state monad. In fact, there's a good chance you'll start wanting that even if you only use snap-core + heist because you'll have to pass HeistState around everywhere you use it.
So I would say that the choice between snap and snap-core is roughly equivalent to the choice between C and assembly language. One might argue that C has these complicated concepts like "for" and "while", but assembly language is much more straightforward with just the simple concept of jmp. But in the end we all know that C seems to have been worth the cognitive overhead because "for" and "while" embody patterns that we use all the time.
However, I will say that there's a good chance you can build a large web app without needing to write your own snaplet. There are a number of useful snaplets out there right now that take care of many common tasks and you can use any of them without actually writing your own standalone snaplet. The only really benefit to writing your own snaplet is if you will use it in more than one web app or if you want to publish it so others can benefit.
It is of course possible but I wouldn't recommend it. Snaplets give you a lot of plumbing, essentially for free - and they don't take much work to get going. If you are going to hand-roll HDBC support and stuff, then presumably you'll want to have your own monad, and an instance of MonadSnap. I'd wager that already this is more complexity than just using snaplets in the first place.
I don't think sticking with snap-core is at all more simple, I'd argue that you're going to produce more confusing code, as you now have to write stuff that is not essential to your application.
Here is a very simple example of me setting up a basic snaplet for a project at work - barely 40 lines of code. Everything you know about snap-core still applies to snaplets (as handlers are instances of MonadSnap).
So no - you don't have to use snaplets, but I would personally strongly recommend them.
I'm trying to visualize some simple automatic physical systems (such things as pendulum, robot arms,etc.) in Haskell.
Often those systems can be described by equations like
df/dt = c*f(t) + u(t)
where u(t) represents some kind of 'intelligent control'. Those systems look to fit very nicely in the Functional Reactive Programming paradigm.
So I grabbed the book "The Haskell School of Expression" by Paul Hudak,
and found that the domain specific language "FAL" (for Functional Animation Language) presented there actually works quite pleasently for my simple toy systems (although some functions, notably integrate, seemed to be a bit too lazy for an efficient use, but easily fixable).
My question is, what's the more mature, up-to-date, well-maintained, performance-tuned alternative for more advanced, or even practical applications today?
This wiki page lists several options for Haskell, but I'm not clear about the following respects:
The status of "reactive", the project from Conal Eliott who is (as I understand it) one of the inventers of this programming paradigm, looks a bit stale. I love his code, but maybe I should try other more up-to-date alternatives? What's the primary difference between them, in terms of syntax/performance/runtime-stability?
To quote from a survey in 2011, Section 6, "... FRP implementations are still not efficient enough or predictable enough in performance to be used effectively in domains which require latency guarantees ...". Alghough the survey suggests some interesting possible optimizations, given the fact that FRP is there for more than 15 years, I get the impression that this performance problem might be something very or even inherently difficult to solve at least within a few years. Is this true?
The same author of the survey talks about "time leaks" in his blog. Is the problem unique to FRP, or something we are generally having when programming in a pure, non-strict language? Have you ever found it just too difficult to stabilize an FRP-based system over time, if not performant enough?
Is this still a research level project? Are the people like plant engineers, robotics engineers, financial engineers, etc. actually using them (in whaterver language that suits their needs)?
Although I personally prefer a Haskell implementation, I'm open to other suggestions. For example, it would be particularly fun to have an Erlang implementation --- it would then be very easy to have an intelligent, adaptive, self-learning server process!
Right now there are mainly two practical Haskell libraries out there for functional reactive programming. Both are maintained by single persons, but are receiving code contributions from other Haskell programmers as well:
Netwire focusses on efficiency, flexibility and predictability. It has its own event paradigm and can be used in areas where traditional FRP does not work, including network services and complex simulations. Style: applicative and/or arrowized. Initial author and maintainer: Ertugrul Söylemez (this is me).
reactive-banana builds on the traditional FRP paradigm. While it is practical to use it also serves as ground for classic FRP research. Its main focus is on user interfaces and there is a ready-made interface to wx. Style: applicative. Initial author and maintainer: Heinrich Apfelmus.
You should try both of them, but depending on your application you will likely find one or the other to be a better fit.
For games, networking, robot control and simulations you will find Netwire to be useful. It comes with ready-made wires for those applications, including various useful differentials, integrals and lots of functionality for transparent event handling. For a tutorial visit the documentation of the Control.Wire module on the page I linked.
For graphical user interfaces currently your best choice is reactive-banana. It already has a wx interface (as a separate library reactive-banana-wx) and Heinrich blogs a lot about FRP in this context including code samples.
To answer your other questions: FRP isn't suitable in scenarios where you need real-time predictability. This is largely due to Haskell, but unfortunately FRP is difficult to realize in lower level languages. As soon as Haskell itself becomes real-time-ready, FRP will get there, too. Conceptually Netwire is ready for real-time applications.
Time leaks aren't really a problem anymore, because they are largely related to the monadic framework. Practical FRP implementations simply don't offer a monadic interface. Yampa has started this and Netwire and reactive-banana both build on that.
I know of no commercial or otherwise large scale projects using FRP right now. The libraries are ready, but I think the people aren't – yet.
Although there are some good answers already, I'm going to attempt to answer your specific questions.
reactive is not usable for serious projects, due to time leak problems. (see #3). The current library with the most similar design is reactive-banana, which was developed with reactive as an inspiration, and in discussion with Conal Elliott.
Although Haskell itself is inappropriate for hard real-time applications, it is possible to use Haskell for soft realtime applications in some cases. I'm not familiar with current research, but I don't believe this is an insurmountable problem. I suspect that either systems like Yampa, or code generation systems like Atom, are possibly the best approach to solving this.
A "time leak" is a problem specific to switchable FRP. The leak occurs when a system is unable to free old objects because it may need them if a switch were to occur at some point in the future. In addition to a memory leak (which can be quite severe), another consequence is that, when the switch occurs, the system must pause while the chain of old objects is traversed to generate current state.
Non-switchable frp libraries such as Yampa and older versions of reactive-banana don't suffer from time leaks. Switchable frp libraries generally employ one of two schemes: either they have a special "creation monad" in which FRP values are created, or they use an "aging" type parameter to limit the contexts in which switches can occur. elerea (and possibly netwire?) use the former, whereas recent reactive-banana and grapefruit use the latter.
By "switchable frp", I mean one which implements Conal's function switcher :: Behavior a -> Event (Behavior a) -> Behavior a, or identical semantics. This means that the shape of the network can dynamically switch as it's run.
This doesn't really contradict #ertes's statement about monadic interfaces: it turns out that providing a Monad instance for an Event makes time leaks possible, and with either of the above approaches it's no longer possible to define the equivalent Monad instances.
Finally, although there's still a lot of work remaining to be done with FRP, I think some of the newer platforms (reactive-banana, elerea, netwire) are stable and mature enough that you can build reliable code from them. But you may need to spend a lot of time learning the ins and outs in order to understand how to get good performance.
I'm going to list a couple of items in the Mono and .Net space and one from the Haskell space that I found not too long ago. I'll start with Haskell.
Elm - link
Its description as per its site:
Elm aims to make front-end web development more pleasant. It
introduces a new approach to GUI programming that corrects the
systemic problems of HTML, CSS, and JavaScript. Elm allows you to
quickly and easily work with visual layout, use the canvas, manage
complicated user input, and escape from callback hell.
It has its own variant of FRP. From playing with its examples it seems pretty mature.
Reactive Extensions - link
Description from its front page:
The Reactive Extensions (Rx) is a library for composing asynchronous
and event-based programs using observable sequences and LINQ-style
query operators. Using Rx, developers represent asynchronous data
streams with Observables, query asynchronous data streams using LINQ
operators, and parameterize the concurrency in the asynchronous data
streams using Schedulers. Simply put, Rx = Observables + LINQ +
Schedulers.
Reactive Extensions comes from MSFT and implements many excellent operators that simplify handling events. It was open sourced just a couple of days ago. It's very mature and used in production; in my opinion it would have been a nicer API for the Windows 8 APIs than the TPL-library provides; because observables can be both hot and cold and retried/merged etc, while tasks always represent hot or done computations that are either running, faulted or completed.
I've written server-side code using Rx for asynchronocity, but I must admit that writing functionally in C# can be a bit annoying. F# has a couple of wrappers, but it's been hard to track the API development, because the group is relatively closed and isn't promoted by MSFT like other projects are.
Its open sourcing came with the open sourcing of its IL-to-JS compiler, so it could probably work well with JavaScript or Elm.
You could probably bind F#/C#/JS/Haskell together very nicely using a message broker, like RabbitMQ and SocksJS.
Bling UI Toolkit - link
Description from its front page:
Bling is a C#-based library for easily programming images, animations,
interactions, and visualizations on Microsoft's WPF/.NET. Bling is
oriented towards design technologists, i.e., designers who sometimes
program, to aid in the rapid prototyping of rich UI design ideas.
Students, artists, researchers, and hobbyists will also find Bling
useful as a tool for quickly expressing ideas or visualizations.
Bling's APIs and constructs are optimized for the fast programming of
throw away code as opposed to the careful programming of production
code.
Complimentary LtU-article.
I've tested this, but not worked with it for a client project. It looks awesome, has nice C# operator overloading that form the bindings between values. It uses dependency properties in WPF/SL/(WinRT) as event sources. Its 3D animations work well on reasonable hardware. I would use this if I end up on a project in need for visualizations; probably porting it to Windows 8.
ReactiveUI - link
Paul Betts, previously at MSFT, now at Github, wrote that framework. I've worked with it pretty extensively and like the model. It's more decoupled than Blink (by its nature from using Rx and its abstractions) - making it easier to unit test code using it. The github git client for Windows is written in this.
Comments
The reactive model is performant enough for most performance-demanding applications. If you are thinking of hard real-time, I'd wager that most GC-languages have problems. Rx, ReactiveUI create some amount of small object that need to be GCed, because that's how subscriptions are created/disposed and intermediate values are progressed in the reactive "monad" of callbacks. In general on .Net I prefer reactive programming over task-based programming because callbacks are static (known at compile time, no allocation) while tasks are dynamically allocated (not known, all calls need an instance, garbage created) - and lambdas compile into compiler-generated classes.
Obviously C# and F# are strictly evaluated, so time-leak isn't a problem here. Same for JS. It can be a problem with replayable or cached observables though.
I'm looking for a way to run an arbitrary Haskell code safely (or refuse to run unsafe code).
Must have:
module/function whitelist
timeout on execution
memory usage restriction
Capabilities I would like to see:
ability to kill thread
compiling the modules to native code
caching of compiled code
running several interpreters concurrently
complex datatype for compiler errors (insted of simple message in String)
With that sort of functionality it would be possible to implement a browser plugin capable of running arbitrary Haskell code, which is the idea I have in mind.
EDIT: I've got two answers, both great. Thanks! The sad part is that there doesn't seem to be ready-to-go library, just a similar program. It's a useful resource though. Anyway I think I'll wait for 7.2.1 to be released and try to use SafeHaskell in my own program.
We've been doing this for about 8 years now in lambdabot, which supports:
a controlled namespace
OS-enforced timeouts
native code modules
caching
concurrent interactive top-levels
custom error message returns.
This series of rules is documented, see:
Safely running untrusted Haskell code
mueval, an alternative implementation based on ghc-api
The approach to safety taken in lambdabot inspired the Safe Haskell language extension work.
For approaches to dynamic extension of compiled Haskell applications, in Haskell, see the two papers:
Dynamic Extension of Typed Functional Languages, and
Dynamic applications from the ground up.
GHC 7.2.1 will likely have a new facility called SafeHaskell which covers some of what you want. SafeHaskell ensures type-safety (so things like unsafePerformIO are outlawed), and establishes a trust mechanism, so that a library with a safe API but implemented using unsafe features can be trusted. It is designed exactly for running untrusted code.
For the other practical aspects (timeouts and so on), lambdabot as Don says would be a great place to look.
I've been curious to understand if it is possible to apply the power of Haskell to embedded realtime world, and in googling have found the Atom package. I'd assume that in the complex case the code might have all the classical C bugs - crashes, memory corruptions, etc, which would then need to be traced to the original Haskell code that
caused them. So, this is the first part of the question: "If you had the experience with Atom, how did you deal with the task of debugging the low-level bugs in compiled C code and fixing them in Haskell original code ?"
I searched for some more examples for Atom, this blog post mentions the resulting C code 22KLOC (and obviously no code:), the included example is a toy. This and this references have a bit more practical code, but this is where this ends. And the reason I put "sizable" in the subject is, I'm most interested if you might share your experiences of working with the generated C code in the range of 300KLOC+.
As I am a Haskell newbie, obviously there may be other ways that I did not find due to my unknown unknowns, so any other pointers for self-education in this area would be greatly appreciated - and this is the second part of the question - "what would be some other practical methods (if) of doing real-time development in Haskell?". If the multicore is also in the picture, that's an extra plus :-)
(About usage of Haskell itself for this purpose: from what I read in this blog post, the garbage collection and laziness in Haskell makes it rather nondeterministic scheduling-wise, but maybe in two years something has changed. Real world Haskell programming question on SO was the closest that I could find to this topic)
Note: "real-time" above is would be closer to "hard realtime" - I'm curious if it is possible to ensure that the pause time when the main task is not executing is under 0.5ms.
At Galois we use Haskell for two things:
Soft real time (OS device layers, networking), where 1-5 ms response times are plausible. GHC generates fast code, and has plenty of support for tuning the garbage collector and scheduler to get the right timings.
for true real time systems EDSLs are used to generate code for other languages that provide stronger timing guarantees. E.g. Cryptol, Atom and Copilot.
So be careful to distinguish the EDSL (Copilot or Atom) from the host language (Haskell).
Some examples of critical systems, and in some cases, real-time systems, either written or generated from Haskell, produced by Galois.
EDSLs
Copilot: A Hard Real-Time Runtime Monitor -- a DSL for real-time avionics monitoring
Equivalence and Safety Checking in Cryptol -- a DSL for cryptographic components of critical systems
Systems
HaLVM -- a lightweight microkernel for embedded and mobile applications
TSE -- a cross-domain (security level) network appliance
It will be a long time before there is a Haskell system that fits in small memory and can guarantee sub-millisecond pause times. The community of Haskell implementors just doesn't seem to be interested in this kind of target.
There is healthy interest in using Haskell or something Haskell-like to compile down to something very efficient; for example, Bluespec compiles to hardware.
I don't think it will meet your needs, but if you're interested in functional programming and embedded systems you should learn about Erlang.
Andrew,
Yes, it can be tricky to debug problems through the generated code back to the original source. One thing Atom provides is a means to probe internal expressions, then leaves if up to the user how to handle these probes. For vehicle testing, we build a transmitter (in Atom) and stream the probes out over a CAN bus. We can then capture this data, formated it, then view it with tools like GTKWave, either in post-processing or realtime. For software simulation, probes are handled differently. Instead of getting probe data from a CAN protocol, hooks are made to the C code to lift the probe values directly. The probe values are then used in the unit testing framework (distributed with Atom) to determine if a test passes or fails and to calculate simulation coverage.
I don't think Haskell, or other Garbage Collected languages are very well-suited to hard-realtime systems, as GC's tend to amortize their runtimes into short pauses.
Writing in Atom is not exactly programming in Haskell, as Haskell here can be seen as purely a preprocessor for the actual program you are writing.
I think Haskell is an awesome preprocessor, and using DSEL's like Atom is probably a great way to create sizable hard-realtime systems, but I don't know if Atom fits the bill or not. If it doesn't, I'm pretty sure it is possible (and I encourage anyone who does!) to implement a DSEL that does.
Having a very strong pre-processor like Haskell for a low-level language opens up a huge window of opportunity to implement abstractions through code-generation that are much more clumsy when implemented as C code text generators.
I've been fooling around with Atom. It is pretty cool, but I think it is best for small systems. Yes it runs in trucks and buses and implements real-world, critical applications, but that doesn't mean those applications are necessarily large or complex. It really is for hard-real-time apps and goes to great lengths to make every operation take the exact same amount of time. For example, instead of an if/else statement that conditionally executes one of two code branches that might differ in running time, it has a "mux" statement that always executes both branches before conditionally selecting one of the two computed values (so the total execution time is the same whichever value is selected). It doesn't have any significant type system other than built-in types (comparable to C's) that are enforced through GADT values passed through the Atom monad. The author is working on a static verification tool that analyzes the output C code, which is pretty cool (it uses an SMT solver), but I think Atom would benefit from more source-level features and checks. Even in my toy-sized app (LED flashlight controller), I've made a number of newbie errors that someone more experienced with the package might avoid, but that resulted in buggy output code that I'd rather have been caught by the compiler instead of through testing. On the other hand, it's still at version 0.1.something so improvements are undoubtedly coming.
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Have you actually "tried" (means programmed in, not just read an article on it) Erlang and decided against it for a project? If so, why? Also, if you have opted to go back to your old language, or to use another functional language like F#, Haskell, Clojure, Scala, or something else then this counts too, and state why.
I returned to Haskell for my personal projects from Erlang for the simple virtue of Haskell's amazing type system. Erlang gives you a ton of tools to handle when things go wrong. Haskell gives you tools to keep you from going wrong in the first place.
When working in a language with a strong type system you are effectively proving free theorems about your code every time you compile.
You also get a bunch of overloading sugar from Haskell's typeclass machinery, but that is largely secondary to me -- even if it does allow me to express a number of abstractions that would be terribly verbose or non-idiomatic and unusable in Erlang (e.g. Haskell's category-extras).
I love Erlang, I love its channels and its effortless scalability. I turn to it when these are the things I need. Haskell isn't a panacea. I give up a better operational understanding of space consumption. I give up the magical one pass garbage collector. I give up OTP patterns and all that effortless scalability.
But its hard for me to give up the security blanket that, as is commonly said, in Haskell, if it typechecks, it is probably correct.
We use Haskell, OCaml and (now) F# so for us it has nothing to do with lack of C-like syntax. Rather we skip Erlang because:
It's dynamically typed (we're fans of Haskell's type system)
Doesn't provide a 'real' string type (I understand why, but it's annoying that this hasn't been corrected at the language level yet)
Tends to have poor (incomplete or unmaintained) database drivers
It isn't batteries included and doesn't appear to have a community working on correcting this. If it does, it isn't highly visible. Haskell at least has Hackage, and I'd guess that's what has us choosing that language over any other. In Windows environments F# is about to have the ultimate advantage here.
There are probably other reasons I can't think of right now, but these are the major points.
The best reason to avoid Erlang is when you cannot commit to the functional way of programming.
I read an anti-Erlang blog rant a few weeks ago, and one of the author's criticisms of Erlang is that he couldn't figure out how to make a function return a different value each time he called it with the same arguments. What he really hadn't figured out is that Erlang is that way on purpose. That's how Erlang manages to run so well on multiple processors without explicit locking. Purely functional programming is side-effect-free programming. You can arm-twist Erlang into working like our ranting blogger wanted, adding side effects, but in doing so you throw away the value Erlang offers.
Pure functional programming is not the only right way to program. Not everything needs to be mathematically rigorous. If you determine your application would be best written in a language that misuses the term "function", better cross Erlang off your list.
I have used Erlang in a few project already. I often use it for restful services. Where I don't use it however is for complex front end web applications where tools like Ruby on Rails are far better. But for the powerbroker behind the scenes I know of no better tool than Erlang.
I also use a few applications written in Erlang. I use CouchDB and RabbitMQ a bit and I have set up a few EJabberd servers. These applications are the most powerful, easiest and flexible tools in their field.
Not wanting to use Erlang because it does not use JVM is in my mind pretty silly. JVM is not some magical tool that is the best in doing everything in the world. In my mind the ability to choose from an arsenal of different tools and not being stuck in a single language or framework is what separates experts from code monkeys.
PS: After reading my comment back in context I noticed it looked like I was calling oxbow_lakes a code monkey. I really wasn't and apologize if he took it like that. I was generalizing about types of programmers and I would never call an individual such a negative name based on one comment by him. He is probably a good programmer even though I encourage him to not make the JVM some sort of a deal breaker.
Whilst I haven't, others on the internet have, e.g.
We investigated the relative merits of
C++ and Erlang in the implementation
of a parallel acoustic ray tracing
algorithm for the U.S. Navy. We found
a much smaller learning curve and
better debugging environment for
parallel Erlang than for
pthreads-based C++ programming. Our
C++ implementation outperformed the
Erlang program by at least 12x.
Attempts to use Erlang on the IBM Cell
BE microprocessor were frustrated by
Erlang's memory footprint. (Source)
And something closer to my heart, which I remember reading back in the aftermath of the ICFP contest:
The coding was very straightforward,
translating pseudocode into C++. I
could have used Java or C#, but I'm at
the point where programming at a high
level in C++ is just as easy, and I
wanted to retain the option of quickly
dropping down into some low-level
bit-twiddling if it came down to it.
Erlang is my other favorite language
for hacking around in, but was worried
about running into some performance
problem that I couldn't extricate
myself from. (Source)
For me, the fact that Erlang is dynamically typed is something that makes me wary. Although I do use dynamically typed languages because some of them are just so very problem-oriented (take Python, I solve a lot of problems with it), I wish they were statically typed instead.
That said, I actually intended to give Erlang a try for some time, and I’ve just started downloading the source. So your “question” achieved something after all. ;-)
I know Erlang since university, but have never used it in my own projects so far. Mainly because I'm mostly developing desktop applications, and Erlang is not a good language for making nice GUIs. But I will soon implement a server application, and I will give Erlang a try, because that's what it's good for. But I'm worring that I need more librarys, so maybe I'll try with Java instead.
A number of reasons:
Because it looks alien from anyone used to the C family of languages
Because I wanted to be able to run on the Java Virtual Machine to take advantage of tools I knew and understood (like JConsole) and the years of effort which have gone into JIT and GC.
Because I didn't want to have to rewrite all the (Java) libraries I've built up over the years.
Because I have no idea about the Erlang "ecosystem" (database access, configuration, build etc).
Basically I am familiar with Java, its platform and ecosystem and I have invested much effort into building stuff which runs on the JVM. It was easier by far to move to scala
I Decided against using Erlang for my project that was going to be run with a lot of shared data on a single multi-processor system and went with Clojure becuase Clojure really gets shared-memory-concurrency. When I have worked on distributed data storage systems Erlang was a great fit because Erlang really shines at distributed message passing systems. I compare the project to the best feature in the language and choose accordingly
Used it for a message gateway for a proprietary, multi-layered, binary protocol. OTP patterns for servers and relationships between services as well as binary pattern matching made the development process very easy. For such a use case I'd probably favor Erlang over other languages again.
The JVM is not a tool, it is a platform. Although I am all in favour of choosing the best tool for the job the platform is mostly already determined. Unless I am developing something standalone, from scratch and without the desire to reuse any existing code/library (three aspects that are unlikely in isolation already) I may be free to choose the platform.
I do use multiple tools and languages but I mainly targetg the JVM platform. That precludes Erlang for most if not all of my projects, as interesting as some of it concepts are.
Silvio
While I liked many design aspects of the Erlang runtime and the OTP platform, I found it to be a pretty annoying program language to develop in. The commas and periods are totally lame, and often require re-writing the last character of many lines of code just to change one line. Also, some operations that are simple in Ruby or Clojure are tedious in Erlang, for example string handling.
For distributed systems relying on a shared database the Mnesia system is really powerful and probably a good option, but I program in a language to learn and to have fun, and Erlang's annoying factor started to outweigh the fun factor once I had gotten past the basic bank account tutorials and started writing plugins for an XMPP server.
I love Erlang from the concurrency standpoint. Erlang really did concurrency right. I didn't end up using erlang primarily because of syntax.
I'm not a functional programmer by trade. I generally use C++, so I'm covet my ability to switch between styles (OOP, imperative, meta, etc). It felt like Erlang was forcing me to worship the sacred cow of immutable-data.
I love it's approach to concurrency, simple, beautiful, scalable, powerful. But the whole time I was programming in Erlang I kept thinking, man I'd much prefer a subset of Java that disallowed data sharing between thread and used Erlangs concurrency model. I though Java would have the best bet of restricting the language the feature set compatible with Erlang's processes and channels.
Just recently I found that the D Programing language offers Erlang style concurrency with familiar c style syntax and multi-paradigm language. I haven't tried anything massively concurrent with D yet, so I can't say if it's a perfect translation.
So professionally I use C++ but do my best to model massively concurrent applications as I would in Erlang. At some point I'd like to give D's concurrency tools a real test drive.
I am not going to even look at Erlang.
Two blog posts nailed it for me:
Erlang machinery walks the whole list to figure out whether they have a message to process, and the only way to get message means walking the whole list (I suspect that filtering messages by pid also involves walking the whole message list)
http://www.lshift.net/blog/2010/02/28/memory-matters-even-in-erlang
There are no miracles, indeed, Erlang does not provide too many services to deal with unavoidable overloads - e.g. it is still left to the application programmer to deal checking for available space in the message queue (supposedly by walking the queue to figure out the current length and I suppose there are no built-in mechanisms to ensure some fairness between senders).
erlang - how to limit message queue or emulate it?
Both (1) and (2) are way below naive on my book, and I am sure there are more software "gems" of similar nature sitting inside Erlang machinery.
So, no Erlang for me.
It seems that once you have to deal with a large system that requires high performance under overload C++ + Boost is still the only game in town.
I am going to look at D next.
I wanted to use Erlang for a project, because of it's amazing scalability with number of CPU'S. (We use other languages and occasionally hit the wall, leaving us with having to tweak the app)
The problem was that we must deliver our application on several platforms: Linux, Solaris and AIX, and unfortunately there is no Erlang install for AIX at the moment.
Being a small operation precludes the effort in porting and maintaining an AIX version of Erlang, and asking our customers to use Linux for part of our application is a no go.
I am still hoping that an AIX Erlang will arrive so we can use it.