y is a Kotlin multiplatform library that aims to port and provide effective concepts inspired by other languages or libraries.

Modules:

y-core:

This module provides core data structures and utility functions.

• Data structures:

  • List:

    val list1 = l<Int>(1,2,3) // (1 2 3)
    val empty = l<Int>() // ()
        
    // From Kotlin's List<E> to PersistentList<E>
    val list2 = listOf<Int>(1, 2, 3).toPlist() // (1 2 3)

    To add an item to a list, use conj(e), it puts the item at the front of the list and returns a new list.

    l<Int>(1,2,3).conj(4) // (4 1 2 3)

    To get the size of a list:

    l<Int>(1,2,3).count // 3

  • Vector:

    val vec1 = v<Int>(1, 2, 3) // [1 2 3]
    val empty = v<Int>() // []
        
    // From Kotlin's List<E> to PersistentVector<E>
    val vec2 = listOf<Int>(1, 2, 3).toPvector() // [1 2 3]

    To add an item to a vector, use conj(e), it puts the item at the end of the vector and returns a new vector.

    v<Int>(1, 2, 3).conj(4) // [1 2 3 4]

    To get the size of a vector:

    v<Int>(1, 2, 3).count // 3

    To get an item by index, you can use get(index) operator or nth(index)/nth(index, def)

    v<Int>(1, 2, 3)[1] // 2
    v<Int>(1, 2, 3).nth(2) // 3
    v<Int>(1, 2, 3).nth(5, -1) // -1

    To get the items in reverse order as a sequence, use reverse()

    v<Int>(1, 2, 3).reverse() // (3 2 1)

  • PersistentArrayMap:

    This map should be only used when you have very small maps and want to maintain key order, since it is just an array of [key,val..key,val]. Subsequent assoc-ing will eventually return a PersistentHashMap.

    val map1 = m<String, Int>("1" to 1, "2" to 2) // {"1" 1, "2" 2}
          
    //From Kotlin's Map<K,V> to PersistentArrayMap<K,V>
    val map2 = mapOf<String, Int>("1" to 1, "2" to 2).toPArrayMap() // {"1" 1, "2" 2}

  • PersistentHashMap:

    This map requires keys that correctly support hashCode and equals.

    val map1 = hashMap<String, Int>("1" to 1, "2" to 2) // {"1" 1, "2" 2}
        
    //From Kotlin's Map<K,V> to PersistentHashMap<K,V>
    val map2 = mapOf<String, Int>("1" to 1, "2" to 2).toPhashMap() // {"1" 1, "2" 2}

  • PersistentHashSet:

    val set1 = hs<Int>(1, 2, 2, 3, 3) // #{1 2 3}
        
    //From Kotlin's Set<E> to PersistentHashSet<E>
    val set2 = setOf<Int>(1, 2, 2, 3 ,3).toPhashSet() // #{1 2 3}

  • Sequence:

    All collections support a member function seq() that return a sequence of type ISeq<E> that can walk the entire collection. A sequance provides three key member functions:

    • first() : return the first element in the sequence.
    • rest() : returns all of the rest elements of the sequence that came after first element, as a sequence.
    • cons(element) : always adds to the front of the sequence and returns a sequence.

  • Keywords (WIP, only on JVM for now):

    Keywords are identifiers that provide very fast equality tests, and they have a string name. If you call toString() on a keyword it returns the name prefixed by a ':' which is not part of the name.

    // To create a Keyword, use the utility function `k(name)`:
    val keyword = k("a") // :a
    
    // invoke(map, default = null) operator
    val map = hashMap("a" to 1)
    val key = k("a")
    val default = k("none")
    key(map, default) // :none