10(?) Functional Java oneliners(?) to impress(?) your friends

TenOneLiners.java

// Ref: http://solog.co/scala/10-scala-one-liners-to-impress-your-friends.html

import static fj.Ord.intOrd;
import static fj.P.p;
import static fj.Show.booleanShow;
import static fj.Show.intShow;
import static fj.Show.listShow;
import static fj.Show.stringShow;
import static fj.data.List.list;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

import com.google.common.io.Files;

import fj.F;
import fj.F2;
import fj.P2;
import fj.Show;
import fj.Unit;
import fj.data.List;
import fj.function.Integers;

public class TenOneLiners {
  public static void main(String[] args) {
    // #1
    final List<Integer> s1 = List.range(1, 11).map(Integers.multiply.f(2));
    listShow(intShow).println(s1);
    
    // #2
    final int s2 = List.range(1, 1001).foldLeft(Integers.add, 0);
    intShow.println(s2);
    
    // #3
    final List<String> words = list("scala", "akka", "play framework", "sbt", "typesafe");
    final String tweet = "This is an example tweet talking about scala and sbt.";
    final boolean exists = words.exists(new F<String, Boolean>() {
      public Boolean f(String s) {
        return tweet.contains(s);
      }
    });
    booleanShow.println(exists);
    
    // #4 (Used Guava here)
    try {
      final File file = new File("data.txt");
      final String fileText = Files.toString(file, Charset.defaultCharset());
      final java.util.List<String> fileLines = Files.readLines(file, Charset.defaultCharset());
      Show.stringShow.println(fileText);
      System.out.println(fileLines);
    } catch (IOException e) {
      e.printStackTrace();
    }
    
    // #5
    List.range(1, 5).map(new F<Integer, String>() {
      public String f(Integer i) {
        return "Happy Birthday " + (i == 3 ? "dear Pradnya" : "to You");
      }
    }).foreach(new F<String, Unit>() {
      public Unit f(String s) {
        return stringShow.println(s);
      }
    });
    
    // #6
    final P2<List<Integer>, List<Integer>> partitions = 
      partition(list(49, 58, 76, 82, 88, 90), new F<Integer, Boolean>() {
        public Boolean f(Integer i) {
          return i < 60;
        }
      });
    final List<Integer> passed = partitions._1();
    final List<Integer> failed = partitions._2();
    listShow(intShow).println(passed);
    listShow(intShow).println(failed);    
    
    // #8
    final int max = list(14, 35, -7, 46, 98).maximum(intOrd);
    final int min = list(14, 35, -7, 46, 98).minimum(intOrd);
    intShow.println(max);
    intShow.println(min);
    
    // #7, #9, #10 - Left as an exercise to the reader.
  }
  
  public static <A> P2<List<A>, List<A>> partition(List<A> list, final F<A, Boolean> predicate) {
    return list.foldLeft(
      new F2<P2<List<A>, List<A>>, A, P2<List<A>, List<A>>>() {
        public P2<List<A>, List<A>> f(P2<List<A>, List<A>> acc, A cur) {
          final List<A> left = acc._1();
          final List<A> right = acc._2();
          if (predicate.f(cur))
            return p(left.cons(cur), right);
          else
            return p(left, right.cons(cur));
        }
      }, 
      p(List.<A> nil(), List.<A> nil())
    );
  }
}

@mnicky: Oh nice, you are a Clojurian. :-) I was preaching to the choir then. I too am looking forward to Java 8. It will greatly aid the adoption of ideas from FP.

Don't know if I would call myself a Clojurian already... rather a clo-newb ;-)

I am learning myself some Haskell. While I am at it, I thought I should give a go to these problems.

import Data.List
import Control.Arrow

a1 :: [Int]
a1 = map (2 *) [1 .. 10]

a2 :: Int
a2 = sum [1 .. 1000] -- Or: foldr 0 (+) [1 .. 1000]

a3 :: Bool
a3 = any (`isInfixOf` tweet) keywords
     where keywords = ["scala", "akka", "play framework", "sbt", "typesafe"]
           tweet = "This is an example tweet talking about scala and sbt."

a4 :: IO ()
a4 = readFile "data.txt" >>= putStrLn

a4' :: IO ()
a4' = readFile "data.txt" >>= (mapM_ putStrLn . lines)

a5 :: IO ()
a5 = mapM_ (putStrLn . s) [1 .. 4]
     where s i = "Happy birthday" ++ if i == 3 then "dear Pradnya" else "to you"

a6 :: ([Int], [Int])
a6 = partition (< 60) [49, 58, 76, 82, 88, 90]     

a7 :: (Int, Int)
a7 = (maximum &&& minimum) [14, 35, -7, 46, 98]