V I O L I N

Violin is a utility library for Kotlin.

It tries to be human-sized, i.e., small enough that its code can be quickly understood without significant time investment. Hence, it focuses on a few orthogonal features and good documentation.

• Presentation
• Installation
• Documentation
• Roadmap
• License (BSD-3)

Presentation

Streams

Violin's main attraction is its stream capabilities.

Streams are best described as iterators, but on which transformations (map, filter, ...) can be applied lazily. Usually the same transformations are applied eagerly on the stream's source (e.g. kotlin.List) or lazily on the source (e.g. kotlin.Sequence). Violin streams are close to Java streams, but (1) allow incremental (not all-at-once) consumption from the stream, and (2) do not complect parallelization with stream processing.

Here is a completely bogus example (you're encouraged to submit a better one!):

1.transitive { it + 1 }
    .dropWhile { it < 10 }
    .upTo { it > 20 }
    .filter { it % 2 == 0 }
    .map { it / 2 }
    .indexed()
    .joinToString(transform = { "${it.index}: ${it.value}" })
    .let { println(it) } // prints "0: 5, 1: 6, 2: 7, 3: 8, 4: 9, 5: 10"

The stream interface is dead simple:

interface Stream <out T: Any> {
    fun stream(): T?
}

Other

• Maybe

• A flexible singly linked list implementation.

• Conversions between functions with and without receivers, over pairs or multiple parameters.

• A stack interface.

• Other stuff

Installation

Manual

Download the latest release and be include it in your classpath.

curl -T https://github.com/norswap/violin/releases/download/0.0.1/violin-0.0.1.jar

Maven

<dependency>
  <groupId>com.norswap</groupId>
  <artifactId>violin</artifactId>
  <version>0.0.1</version>
</dependency>

Gradle

compile 'com.norswap:violin:0.0.1'

Build from Source

You need make, curl and a JDK (8+).

You also need the CLI Kotlin compiler (1.0.3 - superior should be compatible). If you don't have it, run make kotlin to install the 1.0.3 compiler locally before continuing.

make deps
make build
make buildTests
make test
make jar

More targets (docs, clean, ...) available in the makefile.

Documentation

• KDoc (to use violin from Kotlin)
• Javadoc (to use violin from Java)

Roadmap

• Implement fast hashtable using Robin Hood Hashing.
• Implement a fast immutable map using optimized hash-array map tries.