9 ms·

Functional Programming with Java

26 points by srean 16y ago

srean 16y ago
Taken from one of the examples : final HAppend<HCons<Boolean, HNil>, HCons<Double, HCons<String, HCons<Integer[], HNil>>>, HCons<Boolean, HCons<Double, HCons<String, HCons<Integer[], HNil>>>>> one = append(zero); It's here that I miss the repurposed auto keyword of C++ to do some rudimentary type inference.
- timrobinson 16y ago
  final boolean b = a.exists(new F<String, Boolean>() { public Boolean f(final String s) { return fromString(s).forall(isLowerCase); } }); It's here that I miss lambdas to make functional code at all readable.
  - ndunn2 16y ago
    exactly the example I was going to cite. In Scala this would be val b = a.exists(str=>str.forall(_.isLowerCase)) or val b = a.exists(x=>x.toLowerCase() == x) There's no way I'd start using functional programming in Java if it's this clunky. Just stick with Scala.
    - hraberg 16y ago
      Enumerable.java (http://enumerable.org http://enumerable.org) is not really a functional library, but it does support limited closures: boolean b = a.any(λ(s, s.equals(s.toLowerCase())); s and λ are statically imported.
- pmjordan 16y ago
  Or C#'s var keyword, for that matter. Unfortunately, both will only work for local variables. I suspect this is one of the reasons there aren't any popular persistent data structure libraries around for these languages. At least the .NET/C# type system supports covariance/contravariance for functions ("delegates"). Plus, they managed to build F# on it.
  - timrobinson 16y ago
    F# doesn't in fact make use of {co|contra}variance: it only needed generics. (Although F# used to run on .NET 1.x using its own implementation of generics - Don Syme designed both .NET generics and the F# language.) For type inference, you just need a sufficiently smart compiler, although it's much more useful if your language knows about generic types.
    - pmjordan 16y ago
      Thanks for clearing that up (I've yet to try F# in anger). I suppose pre-generics F# did similar type wrangling to Scala's?
      - timrobinson 16y ago
        I don't know about Scala, but yes, wrangling describes well what F# used to do. I never used F# before .NET 2.0, but the techniques it used on 1.x could be interesting -- I'll see if I can find some old documentation... Edit: There used to be a paper describing the technique. I can't find it now, but here's an old Don Syme announcement related to it: http://www.mail-archive.com/dotnet-rotor@discuss.develop.com/msg00424.html http://www.mail-archive.com/dotnet-rotor@discuss.develop.com...
- stephen 16y ago
  Although I was initially skeptical about lombok's "let's hack the private compiler APIs", I must admit that their recent val hack is awesome: http://projectlombok.org/features/val.html http://projectlombok.org/features/val.html I find it frustrating that these guys can hack in "val" but JDK7 has token crap like the "diamond operator".
shooll 16y ago
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moondowner 16y ago
Or even better than using libraries for functional programming in Java, learn and use Scala. You can mix Scala and Java code where needed.
- srean 16y ago
  Or Clojure for that matter.
- sandGorgon 16y ago
  scala != functional programming http://enfranchisedmind.com/blog/posts/scala-not-functional/ http://enfranchisedmind.com/blog/posts/scala-not-functional/ It does have functional programming constructs though Clojure is a much better candidate for FP on the JVM.
  - srean 16y ago
    You are right. But scala does not make it any harder if one chooses to write functional code.
  - gtani 16y ago
    http://enfranchisedmind.com/blog/posts/what-is-a-functional-programming-language/ http://enfranchisedmind.com/blog/posts/what-is-a-functional-... Note: NOT written by same guy who did "Scala not Functional". Everybody has a different definition of FP in mind with these, uh, parameters: - "no hidden side effects"; clearly demarcated IO functions, database calls. - curry, partial function application; lexical closures - TCO - 1st class, higher-order functions - Immutable / persistent collections / data structures Altho most people agree that these are orthogonal to the definition of FP, (but nice to have: - type inference (ML's is variously referred to as Damas-Milner or Hindley-Milner) or static typing - lazy eval - pattern matching - green/lightweight threads with message passing OR STM/MVCC - monads,arrows, functors, CPS http://stackoverflow.com/questions/485418/distinctive-traits-of-the-functional-languages http://stackoverflow.com/questions/485418/distinctive-traits... http://stackoverflow.com/questions/1112773/what-are-the-core-concepts-in-functional-programming http://stackoverflow.com/questions/1112773/what-are-the-core...
mahmud 16y ago
java -jar clojure.jar
badmash69 16y ago
Great Job!! To those wondering why not move to Clojure or Scala instead of this approach, here is why I am holding back: a) I have a mission critical enterprise app that is in maintainance mode. I need to enhance certain features dealing with concurrency -- my team can ramp up Actor model implementation in functionaljava or Jetlang faster than they can ramp up on Scala. b) No doubt that Scala is actually better Java , but I am confident that later versions of JDK would catch up. The concurrency features of JDK 7 are pretty good. c) did I mention the team -- its hard enough finding a good java programmer; imagine how difficult it would be to hire good Scala programmers from the small eclectic community of Scala programmers. d) most of the enterprisey stuff my team develops doesn't require functional programming -- just reliable applications delivered within drop dead deadlines. Plain old Java gets me there . JDK 7 concurrency and various Actor model implementations in Java such as FunctionalJava, Jetlang , Kilim are just cherry on top.
- technomancy 16y ago
  > its hard enough finding a good java programmer; imagine how difficult it would be to hire good Scala programmers from the small eclectic community of Scala programmers. It seems likely that it's hard to find good Java programmers precisely _because_ the skilled devs are tired of Java and see Scala as a way out.
- joshhart 16y ago
  It would be actually easier to hire a good Scala than a good Java programmer because most Scala programmers are good. PG has an essay on this phenomenon somewhere. I'm also not confident that Java will "catch up" to Scala. There's more to Scala than concurrency or functional programming. Type inference, first class objects, short syntax for FP, persistent datastructures, a better object system, etc.
  - badmash69 16y ago
    I agree with your opinion about Scala. However, my point was that Java will continue to be always good enough to steal thunder from more promising languages. ( I realize that Oracle may find a way to screw it up) Had JDK 7 not included Fork/Join and had Actor model implementations such as Jetlang, Kilim and FunctionalJava not been developed, there could have been a strong case to call Java dated and explore Scala in the enterprise. I began exploring Scala / Clojure to deal with multicore CPUs .concurrency etc. but that is no longer a valid concern. Java was never elegant to start with -- it just barely got the job done -- and continues to get the job done and that is good enough. They say that when you have a hammer, everything looks like a Nail. Java is my hammer.
msutherl 16y ago
Does anybody know if there is a library like this for C/C++?
- srean 16y ago
  Take a look at FC++ and Boost.lambda and Boost.Phoenix http://sourceforge.net/projects/fcpp/ http://sourceforge.net/projects/fcpp/ http://www.boost.org/doc/libs/1_45_0/doc/html/lambda.html http://www.boost.org/doc/libs/1_45_0/doc/html/lambda.html http://boost-spirit.com/dl_docs/phoenix-2/libs/spirit/phoenix/doc/html/index.html http://boost-spirit.com/dl_docs/phoenix-2/libs/spirit/phoeni...
- msutherl 16y ago
  After a quick Google, I see there are a few. So I change my question to: has anybody used and liked/disliked one of these libraries or a similar one? The main ones I could find were FC++ and FACT: http://www.cc.gatech.edu/~yannis/fc++/ http://www.cc.gatech.edu/~yannis/fc++/ <http://hci.usask.ca/people/ragu/writings/FunctionalProgrammingInCPP.pdf&#62 http://hci.usask.ca/people/ragu/writings/FunctionalProgrammi...; http://www.fz-juelich.de/jsc/FACT/Old_Pages/fact_index.html http://www.fz-juelich.de/jsc/FACT/Old_Pages/fact_index.html http://www.boost.org/doc/libs/1_45_0/libs/functional/index.html http://www.boost.org/doc/libs/1_45_0/libs/functional/index.h... http://okmij.org/ftp/cpp-digest/Functional-Cpp.html http://okmij.org/ftp/cpp-digest/Functional-Cpp.html or <http://www.haskell.org/haskellwiki/Calling_Haskell_from_C&#62 http://www.haskell.org/haskellwiki/Calling_Haskell_from_C&#6...; :)
  - srean 16y ago
    I have played with FC++ a little bit. Its nice, but if you are used to scheme it will feel verbose. But one cant really complain, C++ wasn't really meant for this.

26 points by srean 16y ago

srean 16y ago

Taken from one of the examples : final HAppend<HCons<Boolean, HNil>, HCons<Double, HCons<String, HCons<Integer[], HNil>>>, HCons<Boolean, HCons<Double, HCons<String, HCons<Integer[], HNil>>>>> one = append(zero); It's here that I miss the repurposed auto keyword of C++ to do some rudimentary type inference.

timrobinson 16y ago
final boolean b = a.exists(new F<String, Boolean>() { public Boolean f(final String s) { return fromString(s).forall(isLowerCase); } }); It's here that I miss lambdas to make functional code at all readable.
- ndunn2 16y ago
  exactly the example I was going to cite. In Scala this would be val b = a.exists(str=>str.forall(_.isLowerCase)) or val b = a.exists(x=>x.toLowerCase() == x) There's no way I'd start using functional programming in Java if it's this clunky. Just stick with Scala.
  - hraberg 16y ago
    Enumerable.java (http://enumerable.org http://enumerable.org) is not really a functional library, but it does support limited closures: boolean b = a.any(λ(s, s.equals(s.toLowerCase())); s and λ are statically imported.
pmjordan 16y ago
Or C#'s var keyword, for that matter. Unfortunately, both will only work for local variables. I suspect this is one of the reasons there aren't any popular persistent data structure libraries around for these languages. At least the .NET/C# type system supports covariance/contravariance for functions ("delegates"). Plus, they managed to build F# on it.
- timrobinson 16y ago
  F# doesn't in fact make use of {co|contra}variance: it only needed generics. (Although F# used to run on .NET 1.x using its own implementation of generics - Don Syme designed both .NET generics and the F# language.) For type inference, you just need a sufficiently smart compiler, although it's much more useful if your language knows about generic types.
  - pmjordan 16y ago
    Thanks for clearing that up (I've yet to try F# in anger). I suppose pre-generics F# did similar type wrangling to Scala's?
    - timrobinson 16y ago
      I don't know about Scala, but yes, wrangling describes well what F# used to do. I never used F# before .NET 2.0, but the techniques it used on 1.x could be interesting -- I'll see if I can find some old documentation... Edit: There used to be a paper describing the technique. I can't find it now, but here's an old Don Syme announcement related to it: http://www.mail-archive.com/dotnet-rotor@discuss.develop.com/msg00424.html http://www.mail-archive.com/dotnet-rotor@discuss.develop.com...
stephen 16y ago
Although I was initially skeptical about lombok's "let's hack the private compiler APIs", I must admit that their recent val hack is awesome: http://projectlombok.org/features/val.html http://projectlombok.org/features/val.html I find it frustrating that these guys can hack in "val" but JDK7 has token crap like the "diamond operator".

shooll 16y ago

( http://www.findsoso.com http://www.findsoso.com / ) (( http://www.findsoso.com http://www.findsoso.com / ) We need your support and trust!!! Dear friends, please temporarily stop your footsteps To our website Walk around A look at Maybe you'll find happiness in your sight shopping heaven and earth You'll find our price is more suitable for you. Welcome to our website ( http://www.findsoso.com http://www.findsoso.com / ) Thanks to the support! ( http://www.findsoso.com http://www.findsoso.com / ) ( http://www.findsoso.com http://www.findsoso.com / ) ( http://www.findsoso.com http://www.findsoso.com /

moondowner 16y ago

Or even better than using libraries for functional programming in Java, learn and use Scala. You can mix Scala and Java code where needed.

srean 16y ago
Or Clojure for that matter.
sandGorgon 16y ago
scala != functional programming http://enfranchisedmind.com/blog/posts/scala-not-functional/ http://enfranchisedmind.com/blog/posts/scala-not-functional/ It does have functional programming constructs though Clojure is a much better candidate for FP on the JVM.
- srean 16y ago
  You are right. But scala does not make it any harder if one chooses to write functional code.
- gtani 16y ago
  http://enfranchisedmind.com/blog/posts/what-is-a-functional-programming-language/ http://enfranchisedmind.com/blog/posts/what-is-a-functional-... Note: NOT written by same guy who did "Scala not Functional". Everybody has a different definition of FP in mind with these, uh, parameters: - "no hidden side effects"; clearly demarcated IO functions, database calls. - curry, partial function application; lexical closures - TCO - 1st class, higher-order functions - Immutable / persistent collections / data structures Altho most people agree that these are orthogonal to the definition of FP, (but nice to have: - type inference (ML's is variously referred to as Damas-Milner or Hindley-Milner) or static typing - lazy eval - pattern matching - green/lightweight threads with message passing OR STM/MVCC - monads,arrows, functors, CPS http://stackoverflow.com/questions/485418/distinctive-traits-of-the-functional-languages http://stackoverflow.com/questions/485418/distinctive-traits... http://stackoverflow.com/questions/1112773/what-are-the-core-concepts-in-functional-programming http://stackoverflow.com/questions/1112773/what-are-the-core...

mahmud 16y ago

java -jar clojure.jar

badmash69 16y ago

Great Job!! To those wondering why not move to Clojure or Scala instead of this approach, here is why I am holding back: a) I have a mission critical enterprise app that is in maintainance mode. I need to enhance certain features dealing with concurrency -- my team can ramp up Actor model implementation in functionaljava or Jetlang faster than they can ramp up on Scala. b) No doubt that Scala is actually better Java , but I am confident that later versions of JDK would catch up. The concurrency features of JDK 7 are pretty good. c) did I mention the team -- its hard enough finding a good java programmer; imagine how difficult it would be to hire good Scala programmers from the small eclectic community of Scala programmers. d) most of the enterprisey stuff my team develops doesn't require functional programming -- just reliable applications delivered within drop dead deadlines. Plain old Java gets me there . JDK 7 concurrency and various Actor model implementations in Java such as FunctionalJava, Jetlang , Kilim are just cherry on top.

technomancy 16y ago
> its hard enough finding a good java programmer; imagine how difficult it would be to hire good Scala programmers from the small eclectic community of Scala programmers. It seems likely that it's hard to find good Java programmers precisely _because_ the skilled devs are tired of Java and see Scala as a way out.
joshhart 16y ago
It would be actually easier to hire a good Scala than a good Java programmer because most Scala programmers are good. PG has an essay on this phenomenon somewhere. I'm also not confident that Java will "catch up" to Scala. There's more to Scala than concurrency or functional programming. Type inference, first class objects, short syntax for FP, persistent datastructures, a better object system, etc.
- badmash69 16y ago
  I agree with your opinion about Scala. However, my point was that Java will continue to be always good enough to steal thunder from more promising languages. ( I realize that Oracle may find a way to screw it up) Had JDK 7 not included Fork/Join and had Actor model implementations such as Jetlang, Kilim and FunctionalJava not been developed, there could have been a strong case to call Java dated and explore Scala in the enterprise. I began exploring Scala / Clojure to deal with multicore CPUs .concurrency etc. but that is no longer a valid concern. Java was never elegant to start with -- it just barely got the job done -- and continues to get the job done and that is good enough. They say that when you have a hammer, everything looks like a Nail. Java is my hammer.

msutherl 16y ago

Does anybody know if there is a library like this for C/C++?

srean 16y ago
Take a look at FC++ and Boost.lambda and Boost.Phoenix http://sourceforge.net/projects/fcpp/ http://sourceforge.net/projects/fcpp/ http://www.boost.org/doc/libs/1_45_0/doc/html/lambda.html http://www.boost.org/doc/libs/1_45_0/doc/html/lambda.html http://boost-spirit.com/dl_docs/phoenix-2/libs/spirit/phoenix/doc/html/index.html http://boost-spirit.com/dl_docs/phoenix-2/libs/spirit/phoeni...
msutherl 16y ago
After a quick Google, I see there are a few. So I change my question to: has anybody used and liked/disliked one of these libraries or a similar one? The main ones I could find were FC++ and FACT: http://www.cc.gatech.edu/~yannis/fc++/ http://www.cc.gatech.edu/~yannis/fc++/ <http://hci.usask.ca/people/ragu/writings/FunctionalProgrammingInCPP.pdf&#62 http://hci.usask.ca/people/ragu/writings/FunctionalProgrammi...; http://www.fz-juelich.de/jsc/FACT/Old_Pages/fact_index.html http://www.fz-juelich.de/jsc/FACT/Old_Pages/fact_index.html http://www.boost.org/doc/libs/1_45_0/libs/functional/index.html http://www.boost.org/doc/libs/1_45_0/libs/functional/index.h... http://okmij.org/ftp/cpp-digest/Functional-Cpp.html http://okmij.org/ftp/cpp-digest/Functional-Cpp.html or <http://www.haskell.org/haskellwiki/Calling_Haskell_from_C&#62 http://www.haskell.org/haskellwiki/Calling_Haskell_from_C&#6...; :)
- srean 16y ago
  I have played with FC++ a little bit. Its nice, but if you are used to scheme it will feel verbose. But one cant really complain, C++ wasn't really meant for this.