Why functional languages

Question

I see a lot of talk on here about functional languages and stuff   Why would you use one over a  traditional  language   What do they do better   What are they worse at   What s the ideal functional programming application

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Lots of people have mentioned Functional Languages.

But some of the Most commonly used Functional Languages in use today besides Javascript.

Excel, SQL, XSLT, XQuery, J and K are used in financial realm.

Of course Erlang.

So I would say that from that list that Functional Programming techniques are used in mainstream every day.

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I don t see anyone mentioning the elephant in the room here  so I think it s up to me     JavaScript is a functional language  As more and more people do more advanced things with JS  especially leveraging the finer points of jQuery  Dojo  and other frameworks  FP will be introduced by the web-developer s back-door    In conjunction with closures  FP makes JS code really light  yet still readable    Cheers  PS

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Most applications are simple enough to be solved in normal OO ways    OO ways have not always been  normal   This decade s standard was last decade s marginalized concept  Functional programming is math  Paul Graham on Lisp  substitute functional programming for Lisp        So the short explanation of why this   1950s language is not obsolete is that   it was not technology but math  and   math doesn   t get stale  The right   thing to compare Lisp to is not 1950s   hardware  but  say  the Quicksort   algorithm  which was discovered in   1960 and is still the fastest   general-purpose sort

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It s not really taught at universities  or is it nowadays     I don t know about nowadays  but I was taught both Miranda and Lisp as part of my CS course in the mid 1990s  Despite not using a pure functional language since  it has influenced the way I solve problems      Most applications are simple enough to be solved in normal OO ways   In the same mid  90s CS course  OO  taught using Eiffel  was taught pretty much on a par with functional programming  Both were non-mainstream at the time  OO may be  normal  now  but it was not ever thus   I ll be interested to see whether F  is the thing that pushes FP into the mainstream

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I don t think that there s any question about the functional approach to programming  catching on   because it s been in use  as a style of programming  for about 40 years  Whenever an OO programmer writes clean code that favors immutable objects  that code is borrowing functional concepts   However  languages that enforce a functional style are getting lots of virtual ink these days  and whether those languages will become dominant in the future is an open question  My own suspicion is that hybrid  multi-paradigm languages such as Scala or OCaml will likely dominate over  purist  functional languages in the same way that pure OO language  Smalltalk  Beta  etc   have influenced mainstream programming but haven t ended up as the most widely-used notations   Finally  I can t resist pointing out that your comments re FP are highly parallel to the remarks I heard from procedural programmers not that many years ago    The  mythical  IMHO   average  programmer doesn t understand it  It s not widely taught  Any program you can write with it can be written another way with current techniques    Just as graphical user interfaces and  code as a model of the business  were concepts that helped OO become more widely appreciated  I believe that increased use of immutability and simpler  massive  parallelism will help more programmers see the benefits that the functional approach offers  But as much as we ve learned in the past 50 or so years that make up the entire history of digital computer programming  I think we still have much to learn  Twenty years from now  programmers will look back in amazement at the primitive nature of the tools we re currently using  including the now-popular OO and FP languages

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F  could catch on because Microsoft is pushing it   Pro    F  is going to be part of next version of Visual Studio  Microsoft is building community for some time now - evangelists  books  consultants that work with high profile customers  significant exposure at MS conferences  F  is first class  Net language and it s the first functional language that comes with really big foundation  not that I say that Lisp  Haskell  Erlang  Scala  OCaml do not have lots of libraries  they are just not as complete as  Net is  Strong support for parallelism    Contra     F  is very hard to start even if you are good with C  and  Net - at least for me    it will probably be hard to find good F  developers    So  I give 50 50 chance to F  to become important  Other functional languages are not going to make it in near future

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In addition to the other answers  casting the solution in pure functional terms forces one to understand the problem better  Conversely  thinking in a functional style will develop better  problem solving skills    Either because the functional paradigm is better or because it will afford an additional angle of attack

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There s a great article from Slava Akhmechet called Functional Programming For The Rest of Us  this was the article that got me into FP btw   Amongst the benefits FP brings  he unorthodoxly emphasizes the following  which I believe contributes to the appeal for software engineers     Unit Testing Debugging Concurrency Hot Code Deployment Machine Assisted Proofs and Optimizations   And then goes on to discuss the goodness of more traditionally discussed aspects of FP like higher order functions  currying  lazy evaluation  optimization  abstracting control structures  although not discussing monads   infinite data structures  strictness  continuations  pattern matching  closures and so on   Highly recommended

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How long did it take OOP to get understood by the average corporate programmer     I was taught functional programming at Utrecht University in - I think - 1994 and only see it start to catch on  in the real world  in the last couple of years  There is no such thing as a  simple application    -    I think that  approaching  side effect free programming for some key parts of software will be essential when we start to get more and more cores in our hardware  Give functional programming a bit more time  And the functional sprinkling in current and future versions of C  will go a long way in preparing those corporate programmers for functional programming without them even realising it

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My view is that it will catch on now that Microsoft have pushed it much further into the mainstream  For me it s attractive because of what it can do for us  because it s a new challenge and because of the job opportunities it resents for the future   Once mastered it will be another tool to further help make us more productive as programmers

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Uh  sorry to be a pedant  but it has already caught on - we call it Excel   http   research microsoft com en-us um people simonpj papers excel   The vast majority of programmes that run on computers are written in Excel or one of the many popular clones of it    there are many programmes that are run many times  and programmes written in Excel tend NOT to be ones of these - most Excel programmes have 1 run instance

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FP is the next best paradigm that is for sure  Now which language could be the next step  That is the hard stuff but I believe could be Haskell  F   Clojure  Ocaml or Erlang  Or could be Python with more FP constructs and better support for parallelism performance or also Perl 6 with parrot looks very interesting

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It seems to me that those people who never learned Lisp or Scheme as an undergraduate are now discovering it   As with a lot of things in this field there is a tendency to hype and create high expectations     It will pass   Functional programming is great   However  it will not take over the world   C  C    Java  C   etc will still be around   What will come of this I think is more cross-language ability - for example implementing things in a functional language and then giving access to that stuff in other languages

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I m always skeptical about the Next Big Thing   Lots of times the Next Big Thing is pure accident of history  being there in the right place at the right time no matter whether the technology is good or not   Examples  C    Tcl Tk  Perl   All flawed technologies  all wildly successful because they were perceived either to solve the problems of the day or to be nearly identical to entrenched standards  or both   Functional programming may indeed be great  but that doesn t mean it will be adopted   But I can tell you why people are excited about functional programming  many  many programmers have had a kind of  conversion experience  in which they discover that using a functional language makes them twice as productive  or maybe ten times as productive  while producing code that is more resilient to change and has fewer bugs   These people think of functional programming as a secret weapon  a good example of this mindset is Paul Graham s Beating the Averages   Oh  and his application   E-commerce web apps   Since early 2006 there has also been some buzz about functional programming and parallelism   Since people like Simon Peyton Jones have been worrying about parallelism off and on since at least 1984  I m not holding my breath until functional languages solve the multicore problem   But it does explain some of the additional buzz right about now   In general  American universities are doing a poor job teaching functional programming   There s a strong core of support for teaching intro programming using Scheme  and Haskell also enjoys some support there  but there s very little in the way of teaching advanced technique for functional programmer   I ve taught such a course at Harvard and will do so again this spring at Tufts   Benjamin Pierce has taught such a course at Penn   I don t know if Paul Hudak has done anything at Yale   The European universities are doing a much better job  for example  functional programming is emphasized in important places in Denmark  the Netherlands  Sweden  and the UK   I have less of a sense of what s happening in Australasia

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I agree with the first point  but times change   Corporations will respond  even if they re late adopters  if they see that there s an advantage to be had   Life is dynamic   They were teaching Haskell and ML at Stanford in the late 90s   I m sure that places like Carnegie Mellon  MIT  Stanford  and other good schools are presenting it to students   I agree that most  expose relational databases on the web  apps will continue in that vein for a long time   Java EE   NET  RoR  and PHP have evolved some pretty good solutions to that problem   You ve hit on something important  It might be the problem that can t be solved easily by other means that will boost functional programming   What would that be   Will massive multicore hardware and cloud computing push them along

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It has already caught on with Map reduce in Hadoop

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Things have been moving in a functional direction for a while  The two cool new kids of the past few years  Ruby and Python  are both radically closer to functional languages than what came before them     so much so that some Lispers have started supporting one or the other as  close enough     And with the massively parallel hardware putting evolutionary pressure on everyone     and functional languages in the best place to deal with the changes     it s not as far a leap as it once was to think that Haskell or F  will be the next big thing

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Functional programming has been around for a long time  since LISP was one of the earliest languages to have a compiler  and since MIT s LISP machines  It s not a new paradigm  OO is much newer  but the dominant software platforms have tended to be written in languages that translate easily to assembly language  and their APIs heavily favor imperative code  UNIX with C  Windows with C  and Macintosh with Pascal and later C    I think the new innovation in the last few years is for a diversity of APIs to catch on  particularly for things like web development where the platform APIs are irrelevant  Since you re not coding directly to the Win32 API or the POSIX API  that gives people the freedom to try out functional languages

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I don t think that functional languages will solve anything  and that this is just a hype that management is trying to sell  remember the only truth   There is no silver bullet   All the rest  is bullshit  also they ve said that OO would solve our problems  that Web Services would solve our problems  that Xml would solve our problems  but in the end the above truth applied  and everything went down  Also  twenty years from now on  who says that we will be using binary computers at all  Why not quantic computers  No one can predict the future  at least not on this planet   That is the second truth

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I think the answer to your question lies more in the statement   the right tool for the job   than the hottest thing   There will always be hot new technologies  and there will always be those who jump on them   Functional languages have been around for a while  it s just now they are getting more press

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Microsoft is really pushing F  with the next version on Visual Studio  It is a hybrid language such as Scala and integrates very nicely with the rest of the  net framework  I think a lot of Microsoft shops are going to use it to speed-up the development of highly parallel data-processing applications and functions

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Most application can be solved in  insert your favorite language  paradigm  etc  here    Although  this is true  different tools can be used to solve different problems  Functional just allows another high  higher   level abstraction that allows to do our jobs more effectively when used correctly

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One key feature in a functional language is the concept of first-class functions  The idea is that you can pass functions as parameters to other functions and return them as values   Functional programming involves writing code that does not change state  The primary reason for doing so is so that successive calls to a function will yield the same result  You can write functional code in any language that supports first-class functions  but there are some languages  like Haskell  which do not allow you to change state  In fact  you re not supposed to make any side effects  like printing out text  at all - which sounds like it could be completely useless   Haskell instead employs a different approach to IO  monads  These are objects that contain the desired IO operation to be executed by your interpreter s toplevel  At any other level they are simply objects in the system   What advantages does functional programming provide  Functional programming allows coding with fewer potentials for bugs because each component is completely isolated  Also  using recursion and first-class functions allows for simple proofs of correctness which typically mirror the structure of the code

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Functional Programming will likely be a tool that is used by Engineers  Scientists to solve the problems that they are facing   It isn t going to take the world like earlier langages   However  the hard product to beat is Excel  if I am an engineer and need to do calculations  Excel is awesome   However  F  is going to be another source and will likely fill design needs by the non-Computer Scientists   Let s face it  Computer Scientists have done a great job of creating a WHOLE new way of doing things   Object Oriented Programming is GREAT   But sometimes you just need a way to solve an equation  get a solution and graph it   That s it   Then a language like F  fills the bill   Or maybe you want to build a finite state machine  F  again could be one of the solutions  but then C could be a solution as well   But when it comes to parallel processing  Excel shines and in time F  will be there as well   In a friendly manner though  F   friendly

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I d point out that everything you ve said about functional languages  most people were saying about object-oriented langauges about 20 years ago   Back then it was very common to hear about OO     The average corporate programmer  e g  most of the people I work with  will not understand it and most work environments will not let you program in it   It s not really taught at universities  or is it nowadays     Most applications are simple enough to be solved in normal IMPERATIVE ways   Change has to come from somewhere   A meaningful and important change will make itself happen regardless of whether people trained in earlier technologies take the opinion that change isn t necessary   Do you think the change to OO was good despite all the people that were against it at the time

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I must be dense  but I still don t get it   Are there any actual examples of small app s written in a functional language like F  where you can look at the source code and see how and why it was better to use such an approach than  say  C

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I think the biggest argument for functional programming languages to become the  next big thing  is that in the future multi-core processors will be the norm   Programmers will have to take advantage of that  and functional programming offers really wonderful possibilities for building top of the line concurrent software   P S  When I was in college at Boston University   98- 02  we spent a semester learning Scheme which is a close cousin of LISP   When we first started learning it  I wanted to rip my hair out   By the end of the course it was very natural

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Have you been following the evolution of programming languages lately  Every new release of all mainstream programming languages seems to borrow more and more features from functional programming    Closures  anonymous functions  passing and returning functions as values used to be exotic features known only to Lisp and ML hackers  But gradually  C   Delphi  Python  Perl  Javascript  have added support for closures  Its not possible for any up-and-coming language to be taken seriously without closures  Several languages  notably Python  C   and Ruby have native support for list comprehensions and list generators  ML pioneered generic programming in 1973  but support for generics   parametric polymorphism   has only become an industry standard in the last 5 years or so  If I remember correctly  Fortran supported generics in 2003  followed by Java 2004  C  in 2005  Delphi in 2008   I know C   has supported templates since 1979  but 90  of discussions on C   s STL start with  here there be demons      What makes these features appealing to programmers  It should be plainly obvious  it helps programmers write shorter code  All languages in the future are going to support -- at a minimum -- closures if they want to stay competitive  In this respect  functional programming is already in the mainstream      Most applications are simple enough to   be solved in normal OO ways   Who says can t use functional programming for simple things too  Not every functional program needs to be a compiler  theorem prover  or massively parallel telecommunications switch  I regularly use F  for ad hoc throwaway scripts in addition to my more complicated projects

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Man cannot understand the perfection and imperfections of his chosen art if he cannot see the value in other arts  Following rules only permits development up to a point in technique and then the student and artist has to learn more and seek further  It makes sense to study other arts as well as those of strategy   Who has not learned something more about themselves by watching the activities of others  To learn the sword study the guitar  To learn the fist study commerce  To just study the sword will make you narrow-minded and will not permit you to grow outward   -- Miyamoto Musashi   A Book of Five Rings

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Because FP has significant benefits in terms of productivity  reliability and maintainability  Many-core may be a killer app that finally gets big corporations to switch over despite large volumes of legacy code Furthermore  even big commercial languages like C  are taking on a distinct functional flavour as a result of many-core concerns - side effects simply don t fit well with concurrency and parallelism   I do not agree that  normal  programmers won t understand it  They will  just like they eventually understood OOP  which is just as mysterious and weird  if not more so    Also  most universities do teach FP  many even teach it as the first programming course

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I think one reason is that some people feel that the most important part of whether a language will be accepted is how good the language is   Unfortunately  things are rarely so simple   For example  I would argue that the biggest factor behind Python s acceptance isn t the language itself  although that is pretty important    The biggest reason why Python is so popular is its huge standard library and the even bigger community of 3rd party libraries   Languages like Clojure or F  may be the exception to the rule on this considering that they re built upon the JVM CLR   As a result  I don t have an answer for them

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Functional Programming has already caught on IMHO  it s just not very visible yet  The strength of such languages is mathematics algorhithms  which is one of the reasons why the Halo Guys use it for their TrueSkill stuff

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The main plus for me is its inherent parallelism  especially as we are now moving away from more MHz and towards more and more cores   I don t think it will become the next programming paradigm and completely replace OO type methods  but I do think we will get to the point that we need to either write some of our code in a functional language  or our general purpose languages will grow to include more functional constructs

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The average corporate programmer  e g    most of the people I work with  will   not understand it and most work   environments will not let you program   in it   That one is just a matter of time though  Your average corporate programmer learns whatever the current Big Thing is  15 years ago  they didn t understand OOP  IF FP catches on  your  average corporate programmers  will follow      It s not really taught at universities    or is it nowadays     Varies a lot  At my university  SML is the very first language students are introduced to  I believe MIT teaches LISP as a first-year course  These two examples may not be representative  of course  but I believe most universities at the very least offer some optional courses on FP  even if they don t make it a mandatory part of the curriculum      Most applications are simple enough to   be solved in normal OO ways   It s not really a matter of  simple enough  though  Would a solution be simpler  or more readable  robust  elegant  performant  in FP  Many things are  simple enough to be solved in Java   but it still requires a godawful amount of code   In any case  keep in mind that FP proponents have claimed that it was the Next Big Thing for several decades now  Perhaps they re right  but keep in mind that they weren t when they made the same claim 5  10 or 15 years ago   One thing that definitely counts in their favor  though  is that recently  C  has taken a sharp turn towards FP  to the extent that it s practically turning a generation of programmers into FP programmers  without them even noticing  That might just pave the way for the FP  revolution   Maybe

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It s catching on because it s the best tool around for controlling complexity   See    - slides 109-116 of Simon Peyton-Jones talk  A Taste of Haskell    -  The Next Mainstream Programming Language  A Game Developer s Perspective  by Tim Sweeney

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Functional languages use a different paradigm than imperative and object-oriented languages  They use side-effect-free functions as a basic building block in the language  This enables lots of things and makes a lot of things more difficult  or in most cases different from what people are used to    One of the biggest advantages with functional programming is that the order of execution of side-effect-free functions is not important  For example  in Erlang this is used to enable concurrency in a very transparent way   And because functions in functional languages behave very similar to mathematical functions it s easy to translate those into functional languages  In some cases  this can make code more readable   Traditionally  one of the big disadvantages of functional programming was also the lack of side effects  It s very difficult to write useful software without IO  but IO is hard to implement without side effects in functions  So most people never got more out of functional programming than calculating a single output from a single input  In modern mixed-paradigm languages like F  or Scala this is easier   Lots of modern languages have elements from functional programming languages  C  3 0 has a lot functional programming features and you can do functional programming in Python too  I think the reasons for the popularity of functional programming is mostly because of two reasons  Concurrency is getting to be a real problem in normal programming because we re getting more and more multiprocessor computers  and the languages are getting more accessible

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Even if you never work in a functional language professionally  understanding functional programming will make you a better developer  It will give you a new perspective on your code and programming in general    I say there s no reason to not learn it   I think the languages that do a good job of mixing functional and imperative style are the most interesting and are the most likely to succeed

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A point missed in the discussion is that the best type systems are found in contemporary FP languages  What s more  compilers can infer all  or at least most  types automatically   It is interesting that one spends half the time writing type names when programming Java  yet Java is by far not type safe  While you may never write types in a Haskell programm  except as a kind of compiler checked documentation  and the code is 100  type safe

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Wow - this is an interesting discussion  My own thoughts on this   FP makes some tasks relatively simple  compared to none-FP languages   None-FP languages are already starting to take ideas from FP  so I suspect that this trend will continue and we will see more of a merge which should help people make the leap to FP easier

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I personally think for distributed systems and multi-threaded parallel programming functional programming will have a break-through soon  As long as it integrates with existing OOP paradigms through programming libraries  So    the purely functional approach - in my opinion - will remain academic

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Some thoughts    The debate between FP and imperative programming  OO  structured  etc   has been raging since Lisp versus Fortran   I think you pose excellent questions but recognize that they are not especially new  Part of the hoopla over FP is that we seem to be recognizing that concurrency is very difficult  and that locks and other mechanisms in OO  e g  Java  are just one solution  FP offers a refreshing sea change with ideas such as Actors and the power of stateless computing  To those wrestling with OO  the landscape seems highly appealing  Yes  schools teach FP  In fact  the University of Waterloo and others offer Scheme in first year classes  reference here   Regarding the average programmer  I m sure that the same arguments were given against C   back in the early 1990s  And look what happened   If businesses can gain an advantage via a technology  you can bet that people will receive training      This is not to say that it is a sure thing  or that there won t be a backlash in 3-5 years  as there always is   However  the trend towards FP has merit and is worth watching

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I don t think most realistic people think that functional programming will catch on  becomes the main paradigm like OO   After all  most business problems are not pretty math problems but hairy imperative rules to move data around and display them in various ways  which means it s not a good fit for pure functional programming paradigm  the learning curve of monad far exceeds OO    OTOH  functional programming is what makes programming fun  It makes you appreciate the  inherent  timeless beauty of succinct expressions of the underlying math of the universe  People say that learning functional programming will make you a better programmer  This is of course highly subjective  I personally don t think that s completely true either   It makes you a better sentient being

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I m actually learning LISP after reading Hackers and Painters and I do believe I will LEARN something from LISP that will give me a better undertanding of everything else I program  Now I dont think I will actually be using LISP in my everyday just because some guy in 1995 created a website that became Yahoo Stores  So its a win-win anyway  if it catches on I win if not  I get more points of views on how to program and how stuff works   Now    on another question kinda related  do I think programming will change a lot with 32 cores procs arriving next year  YES  I dont know if it will be functional programming but    im pretty sure there will be something diferent

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I bet you didn t know you were functional programming when you used    Excel formulas Quartz Composer JavaScript Logo  Turtle graphics  LINQ SQL Underscore js  or Lodash   D3

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I have a hard time envisioning a purely functional language being the common language of the day  the reasons for which I won t get in to  because they re flame fodder   That being said  programming in a functional way can provide benefits no matter the language  if it allows such   For me  it s the ability to test my code much easier  I work with databases a lot    I tend to    write a function that takes data  manipulates it  and returns data write a dead simple wrapper that calls the database and then returns the result of passing that data through my function   Doing so allows me to write unit tests for my manipulation function  without the need to create mocks and the like   I do think purely functional languages are very interesting    I just think it s what we can learn from them that matters to me  not what we can do with them

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When reading  The Next Mainstream Programming Language  A Game Developer   s Perspective  by Tim Sweeney  Epic Games  my first thought was - I got to learn Haskell   PPT  Google s HTML Version

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I don t know whether it will catch on or not  but from my investigations  a functional language is almost certainly worth learning  and will make you a better programmer  Just understanding referential transparency makes a lot of design decisions so much easier- and the resulting programs much easier to reason about  Basically  if you run into a problem  then it tends to only be a problem with the output of a single function  rather than a problem with an inconsistant state  which could have been caused by any of the hundreds of classes methods functions in an imparative language with side effects   The stateless nature of FP maps more naturally to the stateless nature of the web  and thus functional languages lend themselves more easily to more elegant  RESTFUL webapps  Contrast with JAVA and  NET frameworks that need to resort to horribly ugly HACKS like VIEWSTATE and SESSION keys to maintain application state  and maintain the  occasionally quite leaky  abstraction of a stateful imperative language  on an essentially stateless functional platform like the web    And also  the more stateless your application  the more easily it can lend itself to parallel processing  Terribly important for the web  if your website happens to get popular  It s not always straightforward to just add more hardware to a site to get better performance

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