I came across google guice and could not really understand it and what it did, although there seems to be alot of hype around it. I was hoping to get a clojurian perspective of the library and why it is needed/not needed in clojure applications and if there was anything similar built into the language.
Because of Java's OO and type system, dynamically switching between different underlying implementations (for test (mocking) purposes for instance) can be difficult to manage. Libraries like Google Guice are intended to handle these dependency injections in Java more gracefully.
In Clojure and other functional languages functions can be passed around, which makes using different implementations much easier.
There's several ways this can be done in Clojure:
Using your choice of function as parameters in higher order functions.
(Re)Binding your choice of function to a var.
Encapsulating your choice of function inside closures that can then be passed around and called.
Chapter 12 of Clojure Programming has some nice examples of OO patterns like dependency injection and the alternative ways to handle these in Clojure.
Sean Devlin also has a Full Disclojure video on Dependency Injection in Clojure. His example might have been chosen better, though. Instead of using completely different function implementations in his closure, he uses a factory that returns different 'versions' of a function. The gist stays the same though.
Basically, dependency injection is a pattern that is a necessary evil in OOP, and can be solved easily (or is not even a problem) in FP.
The rough Clojure equivalents are still in development. There are two libraries currently in development (as of Oct '12): Prismatic's Graph (not yet open sourced) and Flow by Stuart Sierra.
Note that I consider Guice to be more than dependency injection. It provides a framework for application configuration / modularization. The above libraries aim to accomplish that goal.
Related
Now I'm generally in Java/C# (love both of them, can't really say I'm dedicated to one).
And I've recently been discussing the differences between F# and C# with a friend, when he surprised me saying: "So.. F# sounds a lot like lisp, but with way less 'Swiss-army knife' feel to it."
Now, I was partly ashamed of saying this but I have no idea what lisp was.
After some searching, I saw that lisp is very interesting, but got stumped by the multiple dialects and running environments.
Here is what I know:
I know of 3 dialects:
Common Lisp (I have the Practical Common Lisp book in my bookmarks.
Scheme (a more "theoretical" version of CL)
Clojure. Seems to be a version of CL that runs on JVM.
The basic idea of lisp seems to be about using code as data.
What I want to know:
What is the running environment for different dialects? How do they work/get installed (by this I mean is it a runtime like Java Virtual Machine, or if it requires something else, or if it's supported generally by the OS (as in compiled)). And how to get them (if something is to be gotten)
What is the better dialect to learn (I want the dialect not to be a "learning language" but one you can fully use afterwards without regret of not learning some other one, for example one should first learn C++ before trying out Visual C++, if you know what I mean)
What are the main advantages of lisp in general (I've seen many pages about that saying it's faster in development and execution, but they were all pretty vague about the details)
Can it be generally used for general purpose, or is it concentrated on AI? (By this I mean if, for example, one could make a full console app with it, and then implement OpenGL just as easily and make a game. Learning a language specialized on something precise is worthwhile, but not at the moment for me)
I would also be very happy about any additional details you guys can give me! (Links are appreciated too! E-Books and whatnot.)
Edit: all of the answers here were very useful. As such, I gave them all a +1 to rep, but chose the more concrete one as best. Thank you all.
I also learnt Java and C# intensively before coming to Lisp so hopefully can share some useful perspectives.
Firstly, all Lisps are great and you should definitely consider learning one. There's a famous quote by Eric Raymond:
"Lisp is worth learning for the profound enlightenment experience you
will have when you finally get it; that experience will make you a
better programmer for the rest of your days, even if you never
actually use Lisp itself a lot."
Reasons that Lisps are particularly interesting and powerful are:
Homoiconicity - in Lisp "code is data" - the language itself is written in Lisp data structures. In itself this is interesting, but where it gets really powerful is when you start using this for code generation and advanced macros. Some believe that this features is a key reason why Lisp can help you be more productive than anyone else (short Paul Graham essay)
Interactice development at the REPL - a few other languages also have this, but it is particularly idiomatic and deep-rooted in Lisp culture. It's remarkably productive and liberating to develop while altering a live running program. Recent examples that caught my eye include music hacking with overtone and editing a live game simulation.
Dynamic typing - opinion is more divide on whether this is an advantage or not (I'm personally neutral) but many people thing that dynamically typed langauges give you a productivity advantage, at least in terms of building things quickly. YMMV.
My personal recommendation for a Lisp to learn nowadays would be Clojure. Clojure has a few distinct advantages that make it stand out:
Modern language design - Clojure "refines" Lisp in a number of ways. For example, Clojure adds some new syntax for vectors [] and hashmaps {} in addition to lists (). Purists may disapprove, but I personally believe these find of innovations make the language much nicer to use and read.
Functional first and foremost - all the Lisps are good as functional languages, however Clojure takes it much further. All the standard library is written in terms of pure functions. All data structures are immutable. Mutable state is strictly limited. Lazy sequences (including infinite sequences) are supported. In some senses it feels a bit more like Haskell than the other Lisps.
Concurrency - Clojure has a unique approach to managing concurrency, supported by a very good STM implementation. Worth watching this excellent video for a much deeper explanation.
Runs on the JVM - whatever you think of Java, the JVM is a great platform with extremely good GC, JIT compilation, cross platform portability etc. This can be a barrier to entry for some, but anyone used to Java or C# should quickly feel at home.
Library ecosystem - since Clojure runs on the JVM, it can use Java libraries extremely easily. Calling a Java API from Clojure is trivial - it's just like any other function call with a syntax of (.methodName someObject arg1 arg2). With the availability of the huge Java library ecosystem (mostly open source) Clojure basically leapfrogs all the "niche" languages in terms of practical usefulness
In terms of applications, Clojure is designed to be a fully general purpose langauge so can be used in any field - certainly not limited to AI. I know of people using it in startups, using it for big data processing, even writing games.
Finally on the performance point: you are basically always going to pay a slight performance penalty for using higher level language constructs. However Clojure in my experience is "close enough" to Java or C# that you won't notice the difference for general purpose development. It helps that Clojure is always compiled and that you can use optional type hints to get the performance benefits of static typing.
The flawed benchmarks (as of early 2012) put Clojure within a factor of 2-3 of the speed of statically typed languages like Java, Scala and C#, a little bit behind Common Lisp and a little bit ahead of Scheme (Racket).
Lisp, as you've discovered, is not one language; it's a family of languages that have certain features in common.
There are two primary dialects of Lisp: Common Lisp and Scheme. Each of those two dialects has many implementations, each with their own features. However, both Common Lisp and Scheme are standardized, and the standards define a certain baseline of features which you can expect any implementation to have.
Scheme is a minimalistic language with a very small standard library. It is used primarily by students and theoreticians. Common Lisp has many more language features and a much larger standard library, including a powerful object system, and has been used in large production systems.
Clojure is another minor, more recent dialect. If you want to understand Lisp, you're better off first learning either Common Lisp or Scheme.
My recommendation is to learn Scheme first; it's a purer expression of the ideas that Lisp is made of, and will help you understand the essence of the language. In many ways, Lisp is completely different from Java and other imperative languages; however, what you learn from it will make you a better programmer in those languages. You can easily learn Common Lisp after you know Scheme.
The advantage of Lisp is, simply put, that it's more powerful than other languages. All Lisp code is Lisp data and can be manipulated as such; this allows you to do really cool things with metaprogramming that simply can't be done in other languages, because they don't give you direct access to the data structures that comprise your code. (The reason Lisp can do this and they can't is intimately related to its strange-looking syntax. Every compiler or interpreter, after reading the source code, must translate it into abstract syntax trees. Unlike other languages, Lisp's syntax is a direct representation of the ASTs that Lisp code is translated into, so you know what those trees look like and can manipulate them directly.) The most commonly used metaprogramming feature is macros; Lisp macros can literally translate a bit of source code into anything you can program. You can't do that with, say, C macros.
The "faster in development and execution" thing may have been a reference to one specific feature which most Lisp implementations provide: the read-eval-print loop. You can type an expression into a prompt and the interpreter will evaluate it and print the result. This is wonderful both for learning the language and for debugging or otherwise investigating code.
Lisp is dynamically typed (though statically typed flavors do exist). Most implementations of Lisp run on their own virtual machine; however, many can also be compiled to machine code. Clojure was written specifically to target the JVM; it can also target .NET and JavaScript.
Though originally created for AI research, Lisp is by no means exclusively for AI. The main reason why it's not more popular in mainstream production environments (apart from the self-perpetuating dominance of Java and C#) is library support. Common Lisp has many good libraries out there (Scheme less so), but it pales in comparison to the vast amount of library support available for Java or Python.
If you want to get started, I recommend downloading Racket, a highly popular implementation of Scheme. It has everything you need, including a simple-but-very-powerful IDE with a read-eval-print loop, right out of the box. Though originally developed as a teaching language, it comes with a very large standard library more characteristic of Common Lisp than of Scheme. As a result, it's seeing use in real production environments.
Runtime Environments
Common Lisp and Scheme generally have their own unique runtime environments. There are some variants of Scheme (Chicken and Gambit) which can be translated to C and then linked with their environments so as to be able to be deployed as stand alone executable programs. Clojure runs in the JVM, and there is also a CLR port, but its not clear to me that the CLR port is current with the JVM. Clojure also has Clojurescript, which targets a Javascript runtime.
Which is Better to Learn First
I don't think that question has a good answer. Its up to you. Although if you have experience with the JVM, Clojure might be a bit smoother to start with.
What is Better about Lisp
That's a question liable to start a flame war. I don't have much lisp experience. I started learning Clojure a few months ago in earnest, have looked at Common Lisp and Scheme on and off over the years.
What I like is their dynamic natures. You need to change a function at runtime while your program is running? No problem! Like any power tool, you have to be careful not to chop your bits off when using this.
The power and expressiveness is addicting too. I am able to do some things with little effort that I know I could not achieve in Java, or I know would require a lot more work. Specifically, I was able to put together a description of a data structure - and though the use of macros, delay evaluation of parts of the data until the right time. If I had done that in Java, I would not have been able to nest the declarations like I did because they would have evaluated in the wrong order. Pain would have ensued.
I also like Clojure's view of functional programming, although I have to say it requires work to adjust.
Is Lisp General Purpose
Yes.
--
Mark Volkman has a really good article on Clojure. Many basics are there. One thing that I did in the beginning was to just fire up a repl and experiment when I needed to figure something out programmatically. e.g. explore an API or do some calculations. After a short period of time with that I started working on more building up levels of effort, and I have a project that I'm working on right now that involves Clojure.
There isn't a bad book about Clojure that has been written. The Stuart Sierra book is being updated; and the Oreilly book is about to come out soon, so you might want to wait. The Joy of Clojure is good, but I don't think its a good starter book.
For Common Lisp, I highly recommend the Land of Lisp.
For Scheme, there are several classics including The Little Schemer and SICP.
Oh, and this: http://www.infoq.com/presentations/Are-We-There-Yet-Rich-Hickey (maybe one of the most important talks you'll ever watch), and this http://www.infoq.com/presentations/hickey-clojure (IIRC, really good intro to Clojure).
common lisp
Common Lisp is both compiled and interpreted. Deployments (in Windows) can be done by an exe with DLLs. Or by a precompiled bytecode. Or by installing a Lisp system on the target device and executing the source against it.
Common Lisp is a fully usable industrial language with an active community and libraries for many different tasks.
Lisps are generally faster for development and due to the abstraction capabilities, better at developing higher level concepts. It's hard to explain. Ruby vs. C is an example of this sort of thing. All Lisps carry this capacity IMO.
Common Lisp is a general purpose language. I don't know offhand if modern Common Lisp implementations directly support executing assembly, so it may be difficult to write drivers or use compiler-unsupported CPU instructions.
I like Common Lisp, but Clojure and Racket are not to be sneezed at either. Clojure in particular represents a very interesting track, in my opinion.
For e-books, you can get On Lisp by Graham and Gentle Introduction to Symbolic Computation. Possibly others but those are the ones I can recall.
Context:
An ongoing problem we have been facing is unit testing our market data applications. These applications sit and observe data being retrieved from feeds and does something. Some critical events which are hard to trigger rarely occur and it is are difficult for the Testers to verify our applications perform correctly under all situations, hence we have to rely on unit tests.
These systems generally work by issuing callbacks (into our application) when an event has occurred, then our task to deal with this.
Solution I envision:
Is it possible to embed Python, or extend (not 100% clear on this), so that a tester could fire up a Python REPL and issue function calls that are akin to callbacks which are then handled by our C++ classes. Some form of dynamic manipulation of our objects at runtime.
I do something similar to this in one of my projects by using SWIG to generate python bindings for the relevant parts of the C++ code. Then I embed the interpreter as others have suggested. Having done that I can execute python code at will (e.g. PyRun_SimpleString), which can access C++ code. Normally I end up using something like a Singleton to make accessing specific C++ objects from python easier.
Also worth a mention is directors in swig python modules, which allow virtual functions to be handled much more intuitively. Depending on quite what you're doing you might find these very helpful.
What you want to do is possible, though not trivial to get right. It sounds like you want to embed (rather than extend) Python. Both topics are covered in the tutorial here.
There's quite a lot of work in mapping from C++ classes to Python classes, and there are a number of things that can go wrong in subtle ways, particularly with memory leaks and multithreading (if your existing code is multi-threaded). However, if it's only for use in a testing situation and stability is not mission-critical then it might be less of a problem.
Yes, it is possible. See this for the how.
From some browsing on net, I just understood that any framework is set of libraries provided by the framework and we can simply use those library functions to develop the application.
I would like to know more about
what is a framework with respect to C++.
How are C++ frameworks designed?
How can we use them and develop applications.
Can someone provide me some links to understand the concept of "framework" in C++
A "framework" is something designed to provide the structure of a solution - much as the steel frame of a skyscraper gives it structure, but needs to be fleshed out with use-specific customisations. Both assume some particular problem space - whether it's multi-threaded client/server transactions, or a need for air-conditioned office space, and if your needs are substantively different - e.g. image manipulation or a government art gallery - then trying to use a poorly suited framework is often worse than using none. Indeed, if the evolving needs of your system pass beyond what the framework supports, you may find your options for customising the framework itself are insufficient, or the design you adopted to use it just doesn't suit the re-architected solution you later need. For example, a single-threaded framework encourages you to program in a non-threadsafe fashion, which may be a nightmare to make efficiently multi-threaded post-facto.
They're designed by observing that a large number of programs require a similar solution architecture, and abstracting that into a canned solution framework with facilities for those app-specific customisations.
How they're used depends on the problems they're trying to solve. A framework for transaction dispatch/handling will typically define a way to list IP ports to listen on, nominate functions to be called when connections are made and new data arrives, register timer events that call back to arbitrary functions. XML document, image manipulation, A.I. etc. frameworks would be totally different.... The whole idea is that they each provide a style of use that is simple and intuitive for the applications that might wish to use them.
A big hassle with many frameworks is that they assume ownership of the applications that use them, and relegate the application to a secondary role of filling in some callbacks. If the application needs to use several frameworks, or even one framework with some extra libraries doing e.g. asynchronous communications, then the frameworks may make that very difficult. A good framework is designed more like a set of libraries that the client can control, but need not be confined by. Good frameworks are rare.
More often than not, a framework (as opposed to "just" a library or set of libraries), in OOP languages (including C++), implies a software subsystem that, among other things, supplies classes you're supposed to inherit from, overriding certain methods to specialize the class's functionality for your application's needs, in your application code. If it was just some collection of functions and typedefs it should more properly be called a library, rather than a framework.
I hope this addresses your points 1 and 3. Regarding point 2, ideally, the designers of a framework have a lot of experience designing applications in a certain area, and they "distill" their experience and skill into a framework that lets (possibly less-experienced) developers build their own applications in that area more easily and expeditiously. In the real world, of course, such ideals are not always followed.
With a tool like CppDepend you can analyze any C++ framework, reverse engineer its design in a minute, but also have an accurate idea of the overall code quality of the framework.
An application framework (regardless of language) is a library that attempts to provide a complete framework within which you plug in functionality for your specific application.
The idea is that things like web applications and GUI applications typically require quite a bit of boilerplate to get working at all. The application framework provides all that boilerplate code, and some sort of organization (typically some variation of model-view-controller) where you can plug in the logic specific to your particular application, and it handles most of the other stuff like automatically routing messages and such as needed.
QtConcurrent is awesome.
I'll let the Qt docs speak for themselves:
QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications.
For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system.
There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like.
I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do).
I'm looking for a generic C++ framework that provides the same/similar high-level primitives that QtConcurrent does, and that works with STL collections. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for (but if the requested lib used boost::thread for the low-level work, that would be great).
I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea.
What do you suggest I use?
I've heard good things about Intel's Threaded Building Blocks, though I haven't used it
As of Oct 2009, it doesn't seem to have map-reduce specifically. But people have expressed interest and suggested they were going to come up with something:
http://software.intel.com/en-us/forums/showthread.php?t=65053
"map reduce looks like a simple combination of a filter, a sort, and a reduction but it might need some magic to get it to be efficient"
Can you use Boost? I don't think it provides quite as high-abstraction a layer as Qt, but it should be possible to make one as a reasonably thin facade on top of Boost's primitives (indeed, maybe some of the existing add-ons already provide what you require -- I have to admit I'm not familiar with them in detail, which is why I say "maybe";-).
If you find out that existing add-ons are unsuitable, your facade would be an excellent add-on to contribute to the Boost Vault (or other open-source repo) yourself, "giving back" a useful reusable open-source contribution... I hope this motivates you to do this work if needed!-)
Do you use Luabind, toLua++, or some other library (if so, which one) or none at all?
For each approach, what are the pro's and con's?
I can't really agree with the 'roll your own' vote, binding basic types and static C functions to Lua is trivial, yes, but the picture changes the moment you start dealing with tables and metatables; things go trickier very quickly.
LuaBind seems to do the job, but I have a philosophical issue with it. For me it seems like if your types are already complicated the fact that Luabind is heavily templated is not going to make your code any easier to follow, as a friend of mine said "you'll need Herb Shutter to figure out the compilation messages". Plus it depends on Boost, plus compilation times get a serious hit, etc.
After trying a few bindings, Tolua++ seems the best. Tolua doesn't seem to be very much in development, where as Tolua++ seems to work fine (plus half the 'Tolua' tutorials out there are, in fact, 'Tolua++' tutorials, trust me on that:) Tolua does generate the right stuff, the source can be modified and it seems to deal with complicated cases (like templates, unions, nameless structs, etc, etc)
The biggest issue with Tolua++ seems to be the lack of proper tutorials, pre-set Visual Studio projects, or the fact that the command line is a bit tricky to follow (you path/files can't have white spaces -in Windows at least- and so on) Still, for me it is the winner.
To answer my own question in part:
Luabind: once you know how to bind methods and classes via this awkward template syntax, it's pretty straightforward and easy to add new bindings. However, luabind has a significant performance impact and shouldn't be used for realtime applications. About 5-20 times more overhead than calling C functions that manipulate the stack directly.
I don't use any library. I have used SWIG to expose a C library some time ago, but there was too much overhead, and I stop using it.
The pros are better performance and more control, but its takes more time to write.
Use raw Lua API for your bindings -- and keep them simple. Take inspiration in the API itself (AUX library) and libraries by Lua authors.
With some practice raw API is the best option -- maximum flexibility and minimum of unneeded overhead. You've got what you want and no more, the way you need it to be.
If you must bind large third-party libraries use automated generators like tolua, tolua++ (or even roll your own for the specific case). It would free you from manual work.
I would not recommend using Luabind. At the moment it's development stalled (however starting to come back to life), and if you would meet some corner case, you may be on your own. Also Luabind heavily uses template metaprogramming. This may (and may not) be unacceptable, depending on the point of view.