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Scala is a multi-paradigm language. Maybe because of that, its syntax is very complex. There are frameworks that use just parts of Scala, for instance, cats is more FP. Other frameworks use Scala in a more OOP style (like Java on steroids). Are there any guidelines (or even tools) about using restricted sets of the language? For instance, how to use it in a more FP style?
Twitter published "Effective Scala" in 2012 which is a guide for which parts of Scala they have found useful:
While highly effective, Scala is also a large language, and our experiences have taught us to practice great care in its application. What are its pitfalls? Which features do we embrace, which do we eschew? When do we employ “purely functional style”, and when do we avoid it? In other words: what have we found to be an effective use of the language?
I've read a few questions such as Scala vs Haskell discussing the merits of both languages or which to learn, but I already know that I'd like to learn Scala. I was a Java programmer at uni and now mainly use PHP.
I want to learn Scala as it looks like an improvement on Java for personal projects and I'd also like to learn a functional language to improve my knowledge as a programmer.
I am wondering if it would be a good idea to learn Haskell as an introduction to functional programming as it is purely functional so I'd properly learn it rather than haphazard using bits of functional in Scala without knowing why?
I'd also like to use Haskell for personal projects etc as it looks great, but I don't really see many real world applications of it, seems more used for academic stuff hence wanting to learn it to get the functional understanding then move on to Scala.
Speaking as someone who came from Java, and for whom Scala was a gateway drug to Haskell, I happen to think this is a great idea (learn Haskell first)!
Haskell is conceptually a much simpler language than Scala, and if your goal is to learn how to program functionally, you can't help but do so if you start with Haskell. By design, Scala supports a kind of "legacy mode" of coding in which you don't really have to change your Java (or PHP) habits too much if you don't want to. I think this is a strategic decision--and a good one!--meant to increase adoption amongst crusty Java stalwarts.
But that's not you! You're actually interested in learning something new... so why not go all-out? Learning functional programming in a pure setting, without the clutter and the temptation to regress into old habits, will crystallize the concepts in your brain.
Then by all means return to Scala and learn how it differs from Haskell; it is both weaker in some respects and stronger in others, but you will then be on a much better foundation to appreciate these differences.
I came to Scala from a Java background. Initially I just focused on Scala as a better Java. As time went on I started to use more and more functional concepts in Scala. Eventually I reached a point where I felt I needed a purer understanding of functional programming. It was at this point that I went away and learnt Haskell.
When I cam back to Scala I found it much easier to use a functional style and some of the the concepts I struggled with previously made much more sense.
You don't have to learn Haskell to become a good Scala developers, but I think once you get to a certain level in Scala that having a deeper understanding of functional programming concepts really helps.
I wouldn't do that. If you go straight to Scala (your final aim) you save time. You'll learn functional programming anyway, but as Scala is "less pure" you'll be able to start writing programs in Scala usign some Java-like constructs, which will make the transition simpler.
Even if you go into Haskell, your first programs will be of less "functional quality" than later ones, as only practice improves that. Starting Scala your first programs will be of "less quality" as your first programs in Java or PHP were, but with practice you'll improve. Spending time in unrelated tasks hoping they MAY help, it can result in you wasting that time.
Focus on your aim. If that's Scala, go for it.
UPDATE: I believe this may be relevant to the question. It raises a point on productivity (deliver software) vs seeking "pure knowledge".
The risk of starting directly from Scala, without having played any purely functional programming language first, is that you'll probably be drawn to the procedural solutions a bit too often.
I wouldn't try Haskell as an intro to functional programming, though: not that it's particularly hard - its syntax is amazingly terse - but it's definitely very peculiar (even in the peculiar world of functional programming) and I think you should try with a language you can port more easily to Scala, like Racket or plain Scheme.
To better understand what I mean, look at list comprehensions in Haskell, Scala and Scheme.
I learned Haskell first and then Scala and never regretted. You will gain a much deeper appreciation of FP if you learn Haskell first. Your understanding of the concepts behind FP and why they are important will be seared in. Much of Scala is taken from Haskell (IMHO). It will make more sense when you have the Haskell background. Don't shy away! Your efforts will be rewarded.
For me, I want to learn Scala and functional programming; and, thus simply, I am learning Scala. My study material is Programming Scala. After I have read the early chapter on syntx and stuff, I have skipped chapter covering OO stuff and jumped to Chapter 8 which cover the functional programming stuff. There I let myself struggle with FP.
I read this scala code, which is written in FP way and analyze it. You want to learn Scala for "...an improvement on Java for personal projects." and Haskell for FP intro. So, it seems that first of all, you want to be productive with your java project and then grasp FP as a side effect. To be productive, you have to master the language. There are much to learn and master the language and the only way to master the language is that you have to write the code in that language. As you learn/use Scala, you can't avoid FP out right even if you want to. I have been reading the Scala blogs(the book too) and the authors always go out of their way to do explanation when it comes to FP concept. You don't have to worry about not grasping FP by going Scala route. Yes, you can draw inspiration from Haskell like this when you are learning Scala. Or as Chris Turner above have pointed out, you can delve into more FP when you are already productive with Scala.
You wanna go to point A, why not go to point A directly? If you go via the route of point B (Haskell), you will have to postpone your productivity as Pere Villega mentioned.
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I know there are a few different dialects of Lisp. Having decided that learning Lisp would be a new intellectual experience, I would like to know which Lisp dialect to learn, and why.
Is there one which is more popular than the others? Is any one of them more "complete", as in, better documented and supported? What are the pros and cons of this dialect?
You want to look for a balance between simplicity and cleanliness, attractive features, and a platform that will allow you to write interesting and useful software (to yourself) as well as serve as a learning tool. (This last will keep you going and learning for a lot longer.) Here are some possibilities:
Scheme. Probably the cleanest of all dialects. This is no doubt why The Little Schemer was translated from LISP into Scheme. The fifth Scheme standard specification, R5RS, is a wonderful education in and of itself; it may be the nicest language and library specification I've ever read, as well as the shortest that's reasonably comprehensive. The PLT Scheme (now Racket) platform includes a fairly decent interpreter and compiler, is good for scripting, and also has some visual tools that make it excellent for learning.
Common Lisp. Probably the most portable and comprehensive variant, this is most likely what you want if you want to be writing things such as commercial software. The standard defines extensive libraries, and many more are available beyond that, it has CLOS, which will probably teach you more about OO than any OO language could, and some of the compilers are very good. Disadvantages include some warts that Scheme doesn't have (such as having a separate namespace for variables that refer to functions), not being as clean and simple (as is the case with anything that has had to have the extensions and make the compromises necessary for large applications in the real world), not having hygienic macros, and emphasizing recursion much less than Scheme.
Clojure. This runs on the JVM, which may give it a leg up right there for Java developers. It's got a few warts (e.g., you must explicitly ask for tail call optimization, though this may change one day if TCO is added to the JVM). The macros, while not hygienic, do have some features to help you avoid variable capture, so you can capture variables if you really want to, while running less risk of accidentally doing so than in CL. You've got easy access to all the Java libraries; that's probably a good thing for "real world" code, and fairly pointless in terms of learning. It's got a set of libraries for persistent data structures and support for STM, which make it very interesting from a concurrent point of view; this makes it probably your best bet if you're interested in learning more about new methods of dealing with concurrent and parallel programming. It appears as if Clojure is as usable for large, production applications as Java, in the sense that it's going to have the ability to do the "ugly stuff" you do in production apps that you'd rather not do and don't do when you're learning.
Emacs Lisp. In terms of a LISP, this is not one of the better examples out there. One of its biggest faults is dynamic scoping, but there are many others. However, if you're an Emacs user, this may be the most powerful tool you can learn to improve your use of the editor. How much you'd really learn from learning Emacs Lisp, beyond how to extend Emacs, is for me an open question however; I don't know how often interesting techniques such as high-order functions are really used in Emacs Lisp.
2018 Update
It's been almost a decade since I wrote this post and the Lisp family of languages now appears to be gaining significant traction in the general programmer consciousness. Much of this appears to be related to Clojure which has not only become a properly separate dialect of Lisp in its own right, introducing many of its own good ideas, but also now has a near-identical version targeting JavaScript and has inspired many other Lisps targeting other platforms. For example, Hy targets the CPython AST and bytecode, aiming first for interoperability with Python, but using Clojure ideas "when in doubt." (Though from the latest commits, the latter may be changing a bit.)
The big change this brings in your decision-making process is that you should also be looking at whatever Lisps or Lisp-like languages are available for and interoperate with languages or platforms you already use, be it Perl, Ruby, Erlang, Go or even C++ on microcontrollers.
I would say Scheme, solely because of the Little Schemer, which is one of the most mind-blowingly fun yet extremely hard books I've ever tried to read.
I can recommend Common Lisp on SBCL. This combination is fast, powerful, mature and well-documented.
Also Clojure is a gaining a lot of mindshare these days, and for good reason. Great data structures, profoundly good concurrency support (puts Scheme and CL to shame in this regard), and a great community. It's also relatively simple, CL is as at least as complicated as C++.
This isn't to say I don't enjoy CL or Scheme. I learned Scheme with SICP. And CL brought me to Clojure. It all depends on your goals I suppose. If you want to learn a Lisp that is immensely practical go for Clojure. Otherwise CL or Scheme are both great.
I learned Scheme in school. It was a great learning experience and I will never forget the fundamentals of functional programming. It probably doesn't matter which version of LISP you pick up, as long as you understand the core of its usefulness - stateless lambda calculus.
Here's an interesting article on Why MIT switched from Scheme to Python in its introductory programming course.
I prefer CL, since I like object-oriented programming, and CLOS is the nicest object system around.
I would say all of them, at least at first. Eventually you will probably develop a preference for Scheme or Common Lisp, but they both have enough differences that it's best to get a handle on everything that's out there.
Scheme has continuations for example, and it's good to learn about those in Scheme, even though they can be implemented in Common Lisp.
Learning the difference between lexical and dynamic scope is important, and if you learn both Common Lisp and elisp you'll come across the implications of both.
LFE (Lisp Flavored Erlang) would be nice. You can have the lisp syntax on top of the Erlang VM.
Was a kind of "loaded" question to begin with but OP probably didn't know about it. Generally, Common and Scheme lispers are like PC and Apple computer "people", they don't mix. Which one is best is probably not as relevant as which one "works" for you. Really, there is not that much difference. Likely a preference for one over the other maybe influenced by which one you learn first. (To me, an empty list should be "nothing", known in CL as NIL, and that makes me a Common Lisper.) I like the integration of SBCL with Slime using EMACS, but SBCL is not for everyone. For one thing, SBCL is very strict. If you just want to "have fun" the GNU clisp is easy and available for virtually every platform.
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I develop in Lisp and in Scheme, but I was reading about Clojure and then I want to know, in which cases is better to use it than using Lisp or Scheme? Thanks
This question is impossible to answer. You should use Clojure nearly 100% of the time over CL and Scheme, is what I would say. But that doesn't mean you should listen to me. Others can make a good argument that the opposite is the case.
For me, the syntax and function names in Clojure aesthetically pleasing. Certain Java libraries are invaluable for what I do for data munging and web programming and GUI stuff. Functional programming is challenging and enjoyable. Clojure's flaws are unimportant and outweighed by its benefits in my eyes. Certain intolerable flaws in other Lisps are "fixed" in Clojure, because it's new and it can ignore backwards compatibility. It has a novel and arguably powerful approach to concurrency. The Clojure community is vibrant and welcoming and awesome. All of this says as much about me and what I value as it does about Clojure or other Lisps.
There are libraries for CL and Scheme that don't exist in Clojure or Java. There are people who dislike how Clojure uses too much syntax like [] and {} and want to use parens everywhere. If you want CLOS-style OOP or lots of mutable data structures, another Lisp is arguably better. The JVM is heavyweight, maybe too heavyweight and too much baggage for some people. A lot of Java leaks into Clojure (by design) and this offends some people's sensibilities. The STM and immutable data structures have overheads that make certain things (e.g. number crunching) slower or less elegant. Clojure is new and still rough in certain areas, still rapidly changing and evolving in others. Clojure has yet to pass the test of time, whereas other Lisps already have. Clojure is not a "standard" and some people find a language defined by an implementation to be unappealing. And so on. None of these things matter to me, but they may to you.
This is almost entirely subjective. Which language you should use depends on what you already know, what you are willing to learn, what libraries you want to use, what editors and tools you're comfortable with, what language flaws you're willing to live with and work around and what flaws you can't tolerate, and what helps you get your work done faster, more cheaply, more enjoyably, or achieve whatever your goals are.
Basically, whatever makes you feel warm and fuzzy. Learn them all and then make an informed choice based on your own tastes, and use whichever one you like the best. They're all good.
"Clojure runs on the JVM" means you get the whole cornucopia of Java libraries available. You can make pretty GUIs in Swing, use Apache's Web client or server code, connect a ready-built Sudoku solver... whatever you like.
Another big plus of Clojure is its very polished concurrency support, with about 3 different flavors. If you have a compute-intensive, parallelizable task, Clojure can make it easy. Well, easier.
Update: Another argument. Clojure is pretty strongly functional, so it's a plus if you want to force yourself to think and write functionally.
Clojure should be used when
you need to work with existing java code.
you work with people who are allergic to lisp ("boss, i would like to use a java concurrency library called clojue vs. I would like to re-write this in scheme" [1]
you will be programming for a multi-processor system.
Scheme would be better when:
you need to prove your code is correct. Clojures (call out to java) hinders but does not prevent this.
you are working with people who are allergic to java.
you are developing for a platform with no (new enough) JVM
[1] yes this is a bad bad bad reason. such is the world we live in...
When? As much as possible.
Why? Immutable Data Structures - they really are that good. There are plenty of other reasons too.
ABCL (Armed Bear Common Lisp) and a several of Scheme implementations (KAWA, SISC, ...) are also running on the JVM.
Generally Common Lisp is available in different 'flavors' - ABCL is one of them. Other compile to C, to native code, have extensive development environments or specialized extensions like logic languages or databases.
Clojure OTOH is a new Lisp dialect with emphasis on lazy functional programming and concurrent programming. Its author (Rich Hickey) is a very experienced software developer (he has also written Java and .net interfaces for Common Lisp) and did an excellent job with Clojure. Even though there is some hype around the language, it is worth checking out - it is definitely one of the better Lisp dialects developed in recent years (compared to say Newlisp or Arc).
There are lot's of reasons, some mentioned above. My take is:
The pre-existing libraries. This is such a benefit. I just can't praise this feature enough.
The language is more adapted to the
hardware currently available
(multi-core) and the development
paradigms in use today. It is so much easier to reason about concurrency. The functional aspects are nicer too. You can do functional programming in Lisp, obviously, but it is very easy to break the paradigm unknowingly, unwittingly, and unintentionally.
Cross platform. I run identical
programs on Linux, Windows, and the
Mac. There are lot's of native Lisps
that run across platforms, but
support for all features on all
platforms is a bit spotty and you
constantly have to be on the alert
for things that are missing on one
platform or the other. Likewise,the
libraries you need are not always
consistently supported across
platforms. ABCL and some of the
JVM Scheme implementations have this
consistent support as well, but I
still prefer Clojure because of
point 2.
The nature of the language
community. Let's face it, a lot of
the time the Common Lisp community
is just nasty to deal with. That is
not the case with Clojure at all.
It's easy to get useful help without
the condescension and meanness that
often comes with an answer from the
Common Lisp community. As I have
learned for myself several times,
there is no question so stupid that
you won't get a polite and helpful
reply from the Clojure community.
If I had to find one thing to complain about, it would be IDE support. Maybe it's a question of learning new habits, but it is still easier for me to handle the mechanics of Java development than Clojure. I have tried, and use, Clojure Box, enclojure on NetBeas, La Clojure on Intellij IDEA, and Counterclockwise on Eclipse. They all work fine if you are working primarily from the REPL, but for compilation and execution of class files, they all still feel a bit clumsy.
A subset of Clojure can also compile to javascript
Clojure runs on the JVM (and on the CLR), so there is that.
Clojure's design is concerned with accommodating several styles of concurrent programming safely, deliberately making it difficult to mistakenly write the dangerous, rickety, and often broken concurrency-tolerant code in other languages. If your problem domain involves concurrent programming, Clojure's array of integrated tools for managing concurrency may be a better fit than the implementation-specific or lowest-common-denominator libraries available in other Lisps and Schemes.
One of the greatest things about Clojure is the plethora of libraries you can use with it. You have the power of Java with the expressiveness of Lisp, and that is a badass combination. Clojure is more suited for real world development, because it was made for real world development. With Clojure, you have awesome libraries, awesome modern features, and an amazing community of helpful, like-minded people.
I would have to say that Clojure is a better language, all the way around. That is a highly argumentative statement to make, so I will point out here that this is just my honest opinion.
Clojure rocks.
I'm always trying to learn new languages, so I'm interested in learning Clojure. But, aren't SBCL and some other Common Lisp implementations much, much faster than Clojure? Wouldn't you need considerably more than 4 processors (and a reasonably parallelizable task) to make up for the performance difference between a Clojure app and even a single-threaded SBCL version of the same app?
As a general rule of thumb, I tend to favor Clojure over other languages in cases where either of these fit the bill:
(1). The domain model tends to look very recursive and/or graph-like.
(2). There's an opportunity to leverage a multi-core JVM environment (e.g., Elastic Beanstalk)
(3). There's a fuzzy barrier between data and code (think RPN calculator where nodes can be operators or numbers)
These might sound a bit contrived, but a lot of my work involves dealing with graphs and trees of information, whether it's looking at social networks, some kind of constrained-based optimization, or semantic relationship building. I find that my other favorite language, Ruby, cannot give me the mix of expressiveness and raw computing power compared to Clojure, particularly when it comes to quantitative, recursive, concurrent-type problem solving.
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I've started learning Perl but most of my former programming experience has been in languages that emphasize object oriented programming such as C# and Java. All the Perl examples I have found tend to be long single function programs and I find my self writing code the same way. Are there any resources or tutorials for writing maintainable well structured programs?
Firstly, regardless of what sort of Perl programming you're doing, you'll probably find Perl::Critic to be invaluable. The command-line tool is by far the most convenient for getting feedback on your code, but you there is also a web interface where you can upload your Perl code and receive instant, automated feedback. Note that Perl::Critic isn't going to teach you good structure, but it will help improve your style in general, and steer you away from some common mistakes.
To go with Perl::Critic, I'd recommend getting a copy of Perl Best Practices (PBP). It contains a lot of detailed information upon which Perl::Critic was based. Even if you disagree with particular guidelines in the book, it makes you think about how you code, and that's very, very valuable. You don't have to shell out money for a book, but the two compliment each other very nicely, and there are lengthy discussions you'll find in PBP that you won't get from Perl::Critic.
If you've already worked with other OO languages and OO design, the you'll probably find Moose to be a comfortable transition. Moose is very stable, very well supported, and has a huge and active community (especially via IRC). Moose supersedes almost all the existing OO Perl advice out there, including my own. Object Oriented design is common for a reason; it makes sense for a lot of projects, and there's no reason not to use it in Perl.
Personally, I found a massive improvement in my own program structure when I moved to a test-driven development model. Under such a model, breaking a problem down into small, easily tested units is essential. Start with Test::Tutorial if you're new to testing in Perl and then look at some other testing resources or books if you want to learn more. Use a tool like Devel::Cover or Devel::NYTProf to see what your test cases are hitting and what they're not. Having code that's hard to test is often a sign of poor structure.
Having said all this, the best teacher by far is to get involved with an existing Perl project with experienced contributors. See how they do things, and when you make contributions, think about their advice. If you want a real application with awesome cool value that seems to have sucked up the very best and brightest of the Perl community, then I'd recommend getting involved with Padre, the Perl editor.
If (for whatever reason) you can't get involved with another project, then consider posting code samples to communities such as Stack Overflow, or PerlMonks. Better still, if you can make your code open source, then do so, and solicit feedback. All programming languages are better learnt with others who are already familiar with them, and Perl is no exception here.
May you do Good Magic with Perl,
Paul
Perl Best Practices
If you're learning OO Perl you might as well move on to the next big thing and start learning Moose.
Moose is a postmodern object system for Perl 5 that takes the tedium out of writing object-oriented Perl. It borrows all the best features from Perl 6, CLOS (Lisp), Smalltalk, Java, BETA, OCaml, Ruby and more, while still keeping true to its Perl 5 roots.
Moose is 100% production ready and in heavy use in a number of systems and growing every day.
If you already know how to write well-structured programs and you want to write well-structured Perl, but the only impediment to that is the abundance of ancient, crufty, spaghetti-code examples that are scattered around the net and refuse to die...
Ignore the examples. Or at least ignore their poor structure and only pay attention to the small syntactic bits that you need to learn from.
There is nothing in Perl that pushes you to write bad code. If you already know how to write good code in other languages, then you can apply the exact same principles and practices in Perl. It's merely a matter of discipline, just like in any other language.
If you feel you already are learning the basics and want to improve program structure, then I'd suggest these books, probably best to read in this order:
Intermediate Perl -- this is probably the place to start for what you're asking about; covers developing and using Perl modules (essential for good structure), references, complex data structures, OO, and more
Perl Medic: Transforming Legacy Code -- demonstrates well-structured Perl by showing how to fix poorly-structured Perl
Effective Perl Programming: Writing Better Programs with Perl -- a classic, but still useful; full of Perl idioms that will help you write more Perl-ish Perl; not much on OO, but covers more fundamental coding structures to make your code more succinct and yet more expressive. I think of this as the book that got me from Perl literacy to Perl fluency
All three are best once you've comfortable with basic Perl syntax, but none of them get too far into esoteric advanced concepts that you can't follow if you're still starting out in Perl but have reasonable programming experience in other languages already.
Apart from the sources mentioned above I strongly recommend the book
"Higher-Order Perl" by Mark Jason Dominus.
If you can afford it buy it, otherwise the author has put the book on his website for free as in free beer, Free Higher Order Perl. For the PDF version: direct download URL (1.9 MB).
Edit:
I forgot to mention Perl Design Patterns. The PerlDesignPatterns site is a very good resource or reference for learning Perl design patterns.
Object-Oriented Perl
http://perl.about.com/od/objectorientedperl/Object_Oriented_Perl.htm
http://www.codeproject.com/KB/perl/camel_poop.aspx
http://www.tutorialspoint.com/perl/perl_oo_perl.htm
Personally, I didn't write good OO Perl until I started learning Java. I recommend you spend a small amount of time learning OO in a true OO language and apply what you learn to Perl.
For a place to be mentored, PerlMonks is GREAT.
Write Perl the way you would write C, although you should take advantage of some things BEGIN blocks and modules. It should be formatted so that it looks more or less like old style K&R C code.
As for structure, skip the OO stuff and style it as ADTs instead:
http://en.wikipedia.org/wiki/Abstract_data_type
Basically you do this by using data-structures where you would have used objects in OO (and separating out the algorithms into their own functions).
Then, pick only one way to do things and stick to it, consistency is vital to readability.
If you manage that, the code can be both readable and easy to understand.
Paul.