It has been said that C# can be regarded as a functional programming language, even though it is widely recognized as a OO programming language.
So, what feature set makes C# a functional programming language?
I can only think of:
delegates (even without anonymous methods and lambda expressions)
closures
Anything else?
C# has borrowed a lot of features from ML and Haskell for example:
C# 2.0 brought us parametric polymorphism (or "generics"). I've heard that Dom Syme, one of the creators of F#, was largely responsible for implementing generics in the .NET BCL.
C# 2.0 also allows programmers to pass and returns functions as values for higher-order functions, and has limited support for anonymous delegates.
C# 3.0 and 3.5 improved support anonymous functions for true closures.
LINQ can be considered C#'s own flavor of list comprehensions.
Anonymous types look like an approximation of ML records
Type-inference is a given.
I don't know about you, but C# extension methods look an awful lot like Haskell type classes.
There's been a lot of talk about the "dynamic" keyword in C# 4.0. I'm not 100% sure of its implementation details, but I'm fairly sure its going to use structural typing rather than late binding to retain C#'s compile time safety. Structural typing is roughly equivalent to "duck typing for static languages", its a feature that Haskell and ML hackers have been enjoying for years.
This isn't to say that C# is a functional programming language. Its still missing important features such as pattern matching, tail-call optimization, and list and tuple literals. Additionally, idiomatic C# is fundamentally imperative with a heavy dependence on mutable state.
I wouldn't necessarily consider some of those features mentioned above as exclusive to functional programming languages, but its pretty clear that the C# developers have taken a lot of inspiration from functional programming languages in the past few years.
There being no rigourous definition of "OO Language", "Functional Language", "Procedural Language", one can make arguments that any language fits mostly any classification; one can write procedural Java, object oriented C and functional C++. I typically use a classification based around what the main semantic features support, along with common development practice. A good way of looking at this is to examine builtin and popular frameworks, and see what style they use.
Functional languages are mostly defined as those with first class function primitives, with development styles that use these to reduce complexity with idioms like "map". One other common feature is pattern matching, but I don't see this as exclusively functional. "Pure" functional languages also have no side effects, but that's not mandatory (see how fuzzy these concepts are? :).
So, what's C#? Well, it has first class function style primitives, with delegates (and has gained better syntactic support for the style with anonymous delegates and lambdas). Does this make it functional? Perhaps, if one writes in a functional style. Does the Framework use this style? No, not really.
As such, I wouldn't class C# as functional in general discussion - it is, at best, multi-paradigm, with some functional flavour.
Well, delegates and closures allow it to operate in a largely functional way... for example:
var sum = data.Sum(x=>x.SomeProp);
etc
You can write most higher-order functions using lambdas / delegates. The type inference isn't quite the same as pure functional languages such as F#, but C# generic-type-inference is still pretty good (especially in C# 3.0).
This is especially true in .NET 3.5 and C# 3.0, where LINQ takes a highly-functional approach to many of the problems. But you can still use the functional aspects of C# with .NET 2.0 and C# 2.0. It is just easier with C# 3.0 and lambdas ;-p
Actually, C# is a pragmatic programming language. It aims to make it possible to use a number of paradigms, without punishing you hideously if you want to do something different.
Function pointers is another feature that C# has in the functional category.
I don't think C# is very widely regarded as a functional language, however. I do think it's important to point out that you can program in a functional style in many languages that aren't purely functional.
From Functional Programming:
In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state.
Using that definition, you can program in a functional style in almost any procedural language. Purely functional languages just enforce it.
I mostly agree with the others here who say that C# is better described as multi-paradigm than functional. But I'd add to the examples of functional features in C# LINQ, a first-class and relatively understandable system for writing monads. While purely functional languages don't require the use of monads, the example of Haskell has shown that they can be extremely useful. Yet they're one of the hardest things go grasp for many people new to Haskell. In C#, on the other hand, many people write LINQ queries these days without even realizing that they're writing monads.
you can find a great overview regarding language features in the presentation from Andrew Kennedy (from MS Research) called C# is a functional programming language. My article about functional programming in C# and F# gives an overview from a higher level perspecitve (especially towards the end).
T.
C# has the some functional language features, closures, for example. The .NET libraries aren't written in a functional style, so in practice C# isn't a functional language. Almost everything is accomplished with mutation. The collection types are all mutable.
These are the main points whow makes c# functional
1-Lamba expresions
2-Extension methods
3-Type inferende
4-Object and collection initializators
5-Closures
6-Anonymous types
7-Linq
Related
I just want to point out that this is question is not the reverse of
Best approach for designing F# libraries for use from both F# and C#
Here I'm not asking how to design a functional library written C# to be used in both worlds.
I'd like to know good practices on what design choices embrace or avoid to get a reasonable compromise for make this library usable from F#.
Practices like (for example):
keep object hierarchy as simple as possible
avoid mutating state of objects, but return new ones
etc...
Anyone that already done it, can share it's experience?
Side note
It's interesting note this OSS project, IronJS. Yes, it's written in F#, but the author expose two specialized host IronJS.Hosting.FSharp and IronJS.Hosting.CSharp.
Imagine one day you would like to rewrite your C# library in F# for better usability. Here are the paths you are likely to take:
I focus on the path "Imperative C# --> Functional C# --> Functional F# --> Idiomatic F#". The more functional your C# library is, the more usable your library is in F#. Functional style helps increase composability and is closer to idiomatic F# code. Along these lines, you can:
Embrace immutability by default principle. If you don't know whether you need to update a field/property later, just mark it readonly first.
Follow expression-based and declarative programming style. LINQ operations are good examples.
Use immutable collections or mutable collections in an immutable way. With the introduction of C# immutable collections, it should be easier than ever before.
The picture above is taken from F# for fun and profit's Porting from C# to F# series. They are very helpful; knowing how C# concepts are expressed in F# will improve usability of your library.
It's hard to avoid C#'s object-oriented features. Remember that F# type inference doesn't work very well with these features. Along the line of keeping object hierarchy simple, you should reduce number of member overloads. A big number of member overloads will easily confuse F# type checker. Moreover, it doesn't hurt to distribute a thin F# wrapper with your C# library. Certain things you need to do are turning some methods into module functions and creatingActive Patterns to decompose object hierarchy.
Interop with existing .NET libraries was a major design goal of F#, so there aren't any constraints on the libraries to be consumed.
That said, because of F#'s stricter typing, there are some patterns that result in slightly clunkier code. The builder pattern is one.
var bldr = new StringBuilder();
bldr.Append("abc"); //ignoring return value
vs.
bldr.Append("abc") |> ignore //must be explicitly ignored
But this is easily worked around using an extension method or let-bound function. Bottom line: interop is one of F#'s strengths and greatest achievements.
I just found this web page comparing some code written in Scala, C# and Go. I am astonished to see how close Scala and Go code looks like, much more than Scala code compared to C# code.
So my question is: What are the most significant differences between Scala and Go?
Honestly, that Scala code is written in an extremely imperative style. I'm no functional purist, but contrast that page's Sieve of Eratosthenes code with the much shorter, more legible Sieve of Eratosthenes example at the beginning of the Scaladoc for the Stream class. That page's code has got loads of vars and while-loops, not to mention bitshifts, all over the place. Now, I don't know how much of a consensus there is about what's considered idiomatic Scala code, but this is most definitely nowhere near it. As such, it doesn't say anything about the similarity between Scala and Go other than the fact that they're both descendants of C.
I don't think so, at least conceptually they are very different. Go is much more C++ like and "low level" oriented than C#, and C# has only a few functional features while Scala allows you to write typical "functional" Code (more verbose than OCaml or Haskell, but similar). Scala's type system is quite sophisticated, but is nevertheless based on a Java/C#-like foundation. On the other hand, Go's object-oriented part looks quite different. I didn't try out Go, as I found it too C-like and too low-level. As a Java programmer I know that C# is technically ahead and has a lot of nice features missing in Java. When learning Scala it widened my view, giving me the advantage and power of functional Code without losing the good things from the object oriented world. After the years in Java jail programming in Scala is a really refreshing and mindblowing experience.
Go is just another imperative language which is still in diapers. As of now, Go doesn't have generics. Also there's no support for functional programming.
C# is an OO / imperative language with a very little support for functional programming. Has Generics. Current version doesn't support Covariance and Contravariance annotations (though they're planned for the next version of the language).
Scala is a hybrid language that tries to combine the best of both worlds (namely, OO and functional) into one language. As can be seen from the following figure (Source: http://james-iry.blogspot.com/2010/05/types-la-chart.html), Scala has got a very sophisticated file system, something that both C# and Go lack.
alt text http://www.pogofish.com/types.png
So featurewise, Scala is the most feature-rich language (considering both OO and functional features) of the three. C# does provide some functional constructs but it's nowhere close to Scala. And IMO comparing Go with Scala / C# is like comparing bullock cart with a Lamborghini.
I've seen some people almost directly convert Java code to Go code, C code to Go code, etc. I now see you can almost directly convert Scala code to Go code. When languages have a similar heritage, that's often not hard to do. However, the comparison should be between code written specifically to take advantage of the idioms of a particular language. I recently looked at some pointer dependent C code converted almost directly to Go code. It was not only painful to read; it was also painfully slow.
And, to complement MJP's example of the Sieve of Eratosthenes in Scala, look at the Prime numbers section of A Tutorial for the Go Programming Language for a detailed description of an idiomatic concurrent programming implementation of the Sieve of Eratosthenes in Go.
I've had some interesting debates with colleagues about the merits if incorporating aspect oriented programming as a native paradigm to the C# language.
The debate seems to be divided into three camps:
Those folks who think that C# is already too complicated as it is, and another major feature like AOP would only muddy the waters further.
Those who think that it would be a great addition because anything that can increase the expressiveness of the language without breaking existing is a good thing.
Those who don't think it's necessary because libraries like PostSharp that perform post-compilation IL weaving already allow it in a language neutral way.
I'm curious what the community of C#/.NET developers out there think.
It would be great if languages would make it easier to develop and use AOP extensions.
For instance:
It would be nice if one could give a delegate (or anonymous method, or lambda) as a parameter to a custom attribute. It's not a lot of work to implement this in C#, it's quite easy to implement it in the CLR (since it supports types, why not methods?). And it would allow to express 'pointcuts' in an elegant way.
Support for 'fieldof' and 'methodof'. It is somewhat supported by the CLR (with bugs), not by C#. The same for 'eventof' and 'propertyof' (they have currently no support in the CLR).
Better debugging symbols could make it easier for an aspect weaver to report error messages and give the location in code.
It would be great to have a modular compiler; it would be less expensive to implement some features like source code generation based on aspects (for method and interface introductions).
That said, I don't think that the language should provide AOP extensions. This is too large (I think PostSharp 2.0 is more complex than the C# compiler itself, at least than C# 2.0). Let's face it: AOP is still rather experimental in the sense that we still don't know exactly what we want from it. There is still little experience. But we want the specification of a language to be stable and to address well-understood problems (imagine the Entity Framework were a part of the language).
Additionally, there are different ways to achieve AOP, and build-time is only one of them. There is nothing wrong in using runtime technologies, like JIT-emitted proxies (Spring/Castle); these are just for different use cases and have their own pros and cons.
So my opinion in one sentense: yes for limited and well-defined language extensions that make it easier to develop AOP frameworks; no for a full AOP implementation in the language.
I agree with the first camp. C# is already loaded with features. Leverage the PostSharp library instead.
It would be useful, but many of the uses are being included in various ways as it is. For example, we will have the ability to do post and pre validation in .NET4, which was one use for using around, in aspectJ.
By using extension methods you can inject new methods into objects you may not have source code for.
And, I don't believe it would be used much as C# developers seem to approach problems differently than Java programmers, which is easy to do since the two languages have diverged so much now.
I don't know if the companies that tend to use .NET would want to use something like AOP, and you would need tools to help understand what aspects are being injected where, such as AJDT on Eclipse.
I'd like to know good strategies for deploying a domain-specific-language which must run under at least 2 languages (Java, C#) and probably more (Python, and possibly Javascript).
Some background. We have developed and deployed a domain-specific language currently written in C#. It's deployed though a series of method calls whose arguments are either common language primitives (string, double, etc.), Collections (IEnumerable, HashSet, ...) or objects in a domain-specific library (CMLMolecule, Point3, RealSquareMatrix). The library is well tested and the objects have to comply to a stable deployed XML schema so change will be evolutionary and managed (at least that's the hope).
We hope the language will become used by a wide and partially computer-literate community, used to hacking their own solutions without central control. Ideally the DSL will create a degree of encapsulation and produce the essential functionality they need. The libraries will manage the detailed algorithms which are many and varied but fairly well known. There's a lot in common with the requirements of the DSL in Domain-specific languages vs. library of functions.
I'd appreciate ideas on the best architecture (clearly once it's deployed we cannot easily backtrack). The choices include at least:
Creation of an IDL (e.g. through CORBA). The W3C did this for the XML DOM - I hated it - and it seems to be overkill
manual creation of similar signatures for each platform and best endeavour to keep them in sync.
Creation of a parsable language (e.g. CSS).
declarative programming in XML (c.f. XSLT). This is my preferred solution as it can be searched, manipulated, etc.
Performance is not important. Clarity of purpose is.
EDIT There was discussion as to whether application calls contitute a DSL. I have discovered Martin Fowler's introduction to DSLs (http://martinfowler.com/dslwip/Intro.html) where he argues that simple method calls (or chained calls) can be called a DSL. So a series like:
point0 = line0.intersectWith(plane);
point1 = line1.intersectWith(plane);
midpoint = point0.midpoint(point1);
could be considered a DSL
There seems to be some ambiguity in the question between language and library. The terms "internal DSL" and "external DSL" are useful, and I think are due to Martin Fowler.
An "external" DSL might be a standalone command-line tool. It is passed a string of source, it parses it somehow, and does something with it. There are no real limits on how the syntax and semantics can work. It can also be made available as a library consisting mostly of an eval-like method; a common example would be building a SQL query as a string and calling an execute method in an RDBMS library; not a very pleasant or convenient usage pattern, and horrible if spread around a program on a large scale.
An "internal" DSL is a library that is written in such a way as to take advantage of the quirks of a host (general purpose) language to create the impression that a new language can be embedded inside an existing one. In syntactically-rich languages (C++, C#) this means using operator overloading in ways that seriously stretch (or ignore) the usual meanings of the operator symbols. There are many examples in C++; a few in C# also - the Irony parser toolkit simulates BNF in a fairly restrained way which works well.
Finally, there is a plain old library: classes, methods, properties, with well-chosen names.
An external DSL would allow you to completely ignore cross-language integration problems, as the only library-like portion would be an eval method. But inventing your own tool chain is non-trivial. People always forget the huge importance of debugging, intellisense, syntax highlighting etc.
An internal DSL is probably a pointless endeavour if you want to do it well on C# and Java. The problem is that if you take advantage of the quirks of one host language, you won't necessarily be able to repeat the trick on another language. e.g. Java has no operator overloading.
Which leaves a plain old library. If you want to span C# and Java (at least), then you are somewhat stuck in terms of a choice of implementation language. Do you really want to write the library twice? One possibility is to write the library in Java, and then use IKVM to cross-compile it to .NET assemblies. This would guarantee you an identical interface on both of those platforms.
On the downside, the API would be expressed in lowest-common-denominator features - which is to say, Java features :). No properties, just getX/setX methods. Steer clear of generics because the two systems are quite different in that respect. Also even the standard way of naming methods differs between the two (camelCase versus PascalCase), so one set of users would smell a rat.
If you are willing to re-describe your language using ANTLR you could generate your DSL interpreter in multiple languages without having to manually maintain them including all of the languages you mentioned plus more.
Antlr is a parser/lexer generator and has a large number of target languages. This allows you to describe your language once, without having to maintain multiple copies of it.
See the whole list of target languages here.
Although I do not want to promote my own project too much, I would like to mention PIL, a Platform Independent Language, an intermediate language I have been working on to enable the support of multiple software platforms (like Java, Python, ...), specifically for external DSLs. The general idea is that you generate code in PIL (a subset of Java), which the PIL compiler can then translate to one of many other languages, currently just Java or Python, but more will be added in the future.
I presented a paper about this on the Software and Language Engineering conference about 2 days ago, you can find a link to the publication of the PIL website (pil-lang.org), if you're interested.
Ability to escape to the implementation language in the event you need to do something that just isn't supported by your DSL, or for performance reasons (though I realize that isn't a priority).
I am researching DSL for implementing rules in a rule engine in C#, some of the rules are really complex and may change significantly in the future, so being able to escape out to C# is really useful. Of course this breaks cross-platform compatibility, but it is really just a way of hacking around edge cases without having to change your DSL.
You'd be best off writing the library in C (or some language like rpython which will generate C-code) and then using SWIG or similar to generate the language specific bindings for C#, Java Python etc.
Note that this approach won't help if you are using Javascript in the browser - you'll have to write the javascript library separately. If you are using javascript through Rhino, then you'd be able to just use the Java bindings.
It is possible to interpret JavaScript from inside a Java-program directly using the script engine, and apparently also from C#. Python can be run on the JVM and the .NET engine.
I would suggest that you investigate these options, and then write your library in a common subset of the execution paths available to the language you choose. I would not consider writing it in a language which requires post translation and conversion, since you introduce a step which can be very, very difficult to debug in case of problems.
I would like to expand on Darien's answer. I think that ANTLR brings something to the table that few other lexer/parser tools provide (at least to my knowledge). If you would like to create a DSL which ultimately generates Java and C# code, ANTLR really shines.
ANTLR provides four fundamental components:
Lexer Grammar (break down input streams into tokens)
Parser Grammar (organize tokens into an abstract syntax tree)
Tree Grammar (walk the abstract syntax tree and pipe the metadata into a template engine)
StringTemplate (a template engine based on functional programming principles)
Your lexer,parser, and tree grammars can remain independent of your final generated language. In fact, the StringTemplate engine supports logical groups of template definitions. It even provides for interface inheritance of template groups. This means you can have third parties use your ANTLR parser to create say python, assembly, c, or ruby, when all you initially provided was java and C# output. The output language of your DSL can easily be extended as requirements change over time.
To get the most out of ANTLR you will want to read the following:
The Definitive ANTLR Reference: Building Domain-Specific Languages
Language Implementation Patterns: Create Your Own Domain-Specific and General Programming Languages
I know Java well. Which caveats and resources will help me cross to the other side (C#) as painlessly as possible.
Biggest tip: go with the .NET naming conventions from the word go. That way you'll constantly be reminded about which language you're in. (Sounds silly, but it really is helpful.) Embrace the idioms of the language as far as possible.
There are various books specifically for folks in your situation - search for "C# for Java" in Amazon and you'll get plenty of hits. It's worth reading carefully to make sure you don't assume that things will work the same in C# as in Java. (For instance, in C# instance variable initializers are executed before the base class constructor body; in Java they happen after. Subtle things like this can take a while to learn, and are easy to miss if you're skimming.)
If you're going to be using C# 3, I'd get a book which definitely covers that - everything in C# 3 will be new to you. Gratuitous plug: my own book (C# in Depth) covers C# 2 and 3, but assumes you already know C# 1. (In other words, it won't be enough on its own, but you may want it as a "second" book.)
See this great article on C# from a Java Developer's Perspective. It has several insights on the things that can be done in both sides to avoid minimum overhead. Having example in both the language you know and the language you want to learn eases the learning curve quite a bit.
Install Visual Studio 2008 and Resharper with IntelliJ IDEA key bindings. This gives you things like prompting you to include namespaces if you start using them.
Start a new project and start writing Java code, when you run into something that doesn't work properly or it's unable to find the class you're trying to use Google "PrintLn in c#".
Write tests or code snippets for sanity checks, like you may want to check if == works for strings (it does)
realize that c# alias Data Types (int is an alias for System.Int32, string for System.String)
look at other peoples code I recommend JP Boodhoos Google code
Take a job in C#, there's lots of jobs requiring both Java and C# especially in support.
Know your libraries, most Java libraries have been ported and most of the time the name is either like (Hibernate => NHibernate) or (Xstream => Xstream.Net). Not every library has an obvious name so just start looking into random ones you hear about here. ie (Rhino.Mocks,HTMLAgilityPack,MBUnit,Rhino.Commons,Castle Project)
Go to usergroup meetings look for a DNUG (Dot Net User Group) they'll be helpful and you can get some good advice.
There's a cheat-sheet from Microsoft for Java developers using C# :)
I know that a good answer has already been accepted. However, I'd like to make an addition...
I find that learning a new language typically involves learning subtle syntactic differences....especially when dealing with the difference between languages in the C/C++/Java/C# family.
In addition to a nice thick reference book I recommend getting a pocket reference like C# 3 Pocket Reference from O'Reilly. It won't help you with the design patterns etc...but will provide a very quick reference about the specific differences of the language you are using.
Here's a quick blurb about this book from that site:
C# 3.0 Pocket Reference includes plenty of illustrations and code examples to explain:
Features new to C# 3.0, such as lambda expressions, anonymous types, automatic properties, and more
All aspects of C# syntax, predefined types, expressions, and operators
Creating classes, structs, delegates and events, enums, generics and constraints, exception handling, and iterators
The subtleties of boxing, operating overloading, delegate covariance, extension method resolution, interface reimplementation, nullable types, and operating lifting
LINQ, starting with the principles of sequences, deferred execution and standard query operators, and finishing with a complete reference to query syntax-including multiple generators, joining, grouping, and query continuations
Consuming, writing, and reflecting on custom attributes
I used this book (well the original) to help me go from being a Java to a C# developer. While I was learning, I kept it by my desk at all times and it really helped.
I made the transition pretty easily by using C# at work, but one of the most important things to do is familiarize yourself with the .NET API and some of the powerful techniques available in C#.
After I learned the .net library I relied on it a lot more than I used to, so learning about the things it can do for you is very helpful. After that, if you work with db code at all, learn LINQ, and also techniques lambas, anonymous types and delegates are also a useful to pick up.
The language syntax is vary similar, so I should only read a small reference of the C# syntax. Like a simple book (for experienced programmers) or maybe wikipedia (http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp) will tell enough.
The biggest difference is the library: Asp.Net websites are totally different from java servlets.
Don't read much, just start programming!
Here's a link that has syntax comparison between Java and C# (even though it's almost identical, there are a few differences).
http://www.harding.edu/fmccown/java1_5_csharp_comparison.html
Use Sharpen to convert your Java programs to C# and see the differences.