Another functional library for Java
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Another functional library for Java

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A functional library for Java that has the following features

  • Tries to be as lazy as possible just like Clojure's collection library
  • Works with Iterable, Iterator, Arrays, Char Sequences, Dates and Numbers (i.e virtually everything)
  • Follows the ML family of function / method names (Standard ML, oCaml, F#, Scala, Haskell)
  • Uses and extends Callable interface for maximum interop (i.e Can use with Clojure, Hazelcast)
  • Optionally supports using Hamcrest matchers as predicates
  • Supports chaining of all methods (Recommended) or the use of static imports for all methods.
  • Contains PersistentSet, PersistentMap, PersistentSortedMap, PersistentList
  • Support Functors and Applicative Functors
  • Supports runtime multi-method dispatch and pattern matching

Tail call optimisation is available in conjunction with JCompilo

Now also available in Objective-C


The following are some simple examples of actual Java code (minus any imports). They are using numbers just to make them simple but these could just as well be any types; though you would either need to create some strongly types predicates / callables for your types or use the provided dynamic proxy support.

sequence(1, 2, 3, 4).filter(even); // lazily returns 2,4
sequence(1, 2).map(toString); // lazily returns "1", "2"
sequence(1, 2).mapConcurrently(toString); // lazily distributes the work to background threads
sequence(1, 2, 3).take(2); // lazily returns 1,2
sequence(1, 2, 3).drop(2); // lazily returns 3
sequence(1, 2, 3).tail(); // lazily returns 2,3
sequence(1, 2, 3).head(); // eagerly returns 1
sequence(1, 2, 3).reduce(sum); // eagerly return 6
sequence(1, 3, 5).find(even); // eagerly returns none()
sequence(1, 2, 3).contains(2); // eagerly returns true
sequence(1, 2, 3).exists(even); // eagerly return true
sequence(1, 2, 3).forAll(odd); // eagerly returns false;
sequence(1, 2, 3).foldLeft(0, add); // eagerly returns 6
sequence(1, 2, 3).toString(); // eagerly returns "1,2,3"
sequence(1, 2, 3).toString(":"); // eagerly returns "1:2:3"


range(1, 4); // lazily returns 1,2,3,4
repeat("car"); // lazily returns an infinite sequence of "car"s
iterate(increment, 1); // lazily returns 1,2,3 ... to infinity
range(1, 4).cycle(); // lazily returns 1,2,3,4,1,2,3,4,1,2,3,4 infinitely 
primes(); // lazily returns every prime number
fibonacci(); // lazily returns the fibonacci sequence
powersOf(3); // lazily returns the powers of 3 (i.e 1,3,9,27 ...)

Naturally you can combine these operations together ...

iterate(increment, 1).filter(even).take(10).reduce(average); // returns 11

And because all the operations except reduce are lazy the sequence of numbers is only processed once.


  • Stable releases are version 1.x (Require Java 7+) Branch:java7
  • Development releases are version 2.x (Require Java 8+) HEAD

All releases are created automically and released to

This is a maven repository so you can just add the following in you repo section


and then



Apache 2


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