List[A: A]
A doubly linked list.
(The following is paraphrased from Wikipedia.)
A doubly linked list is a linked data structure that consists of a set of sequentially linked records called nodes. (Implemented in Ponylang via the collections.ListNode class.) Each node contains four fields: two link fields (references to the previous and to the next node in the sequence of nodes), one data field, and the reference to the in which it resides. A doubly linked list can be conceptualized as two singly linked lists formed from the same data items, but in opposite sequential orders.
As you would expect. functions are provided to perform all the common list operations such as creation, traversal, node addition and removal, iteration, mapping, filtering, etc.
Example program
There are a lot of functions in List. The following code picks out a few common examples.
It outputs:
A new empty list has 0 nodes. Adding one node to our empty list means it now has a size of 1. The first (index 0) node has the value: A single String A list created by appending our second single-node list onto our first has size: 2 The List nodes of our first list are now: A single String Another String Append *moves* the nodes from the second list so that now has 0 nodes. A list created from an array of three strings has size: 3 First Second Third Mapping over our three-node list produces a new list of size: 3 Each node-value in the resulting list is now far more exciting: First BOOM! Second BOOM! Third BOOM! Filtering our three-node list produces a new list of size: 2 Second BOOM! Third BOOM! The size of our first partitioned list (matches predicate): 1 The size of our second partitioned list (doesn't match predicate): 1 Our matching partition elements are: Second BOOM!
use "collections"
actor Main
new create(env:Env) =>
// Create a new empty List of type String
let my_list = List[String]()
env.out.print("A new empty list has " + my_list.size().string() + " nodes.") // 0
// Push a String literal onto our empty List
my_list.push("A single String")
env.out.print("Adding one node to our empty list means it now has a size of "
+ my_list.size().string() + ".") // 1
// Get the first element of our List
try env.out.print("The first (index 0) node has the value: "
+ my_list.index(0)?()?.string()) end // A single String
// Create a second List from a single String literal
let my_second_list = List[String].unit("Another String")
// Append the second List to the first
my_list.append_list(my_second_list)
env.out.print("A list created by appending our second single-node list onto our first has size: "
+ my_list.size().string()) // 2
env.out.print("The List nodes of our first list are now:")
for n in my_list.values() do
env.out.print("\t" + n.string())
end
// NOTE: this _moves_ the elements so second_list consequently ends up empty
env.out.print("Append *moves* the nodes from the second list so that now has "
+ my_second_list.size().string() + " nodes.") // 0
// Create a third List from a Seq(ence)
// (In this case a literal array of Strings)
let my_third_list = List[String].from(["First"; "Second"; "Third"])
env.out.print("A list created from an array of three strings has size: "
+ my_third_list.size().string()) // 3
for n in my_third_list.values() do
env.out.print("\t" + n.string())
end
// Map over the third List, concatenating some "BOOM!'s" into a new List
let new_list = my_third_list.map[String]({ (n) => n + " BOOM!" })
env.out.print("Mapping over our three-node list produces a new list of size: "
+ new_list.size().string()) // 3
env.out.print("Each node-value in the resulting list is now far more exciting:")
for n in new_list.values() do
env.out.print("\t" + n.string())
end
// Filter the new list to extract 2 elements
let filtered_list = new_list.filter({ (n) => n.string().contains("d BOOM!") })
env.out.print("Filtering our three-node list produces a new list of size: "
+ filtered_list.size().string()) // 2
for n in filtered_list.values() do
env.out.print("\t" + n.string()) // Second BOOM!\nThird BOOM!
end
// Partition the filtered list
let partitioned_lists = filtered_list.partition({ (n) => n.string().contains("Second") })
env.out.print("The size of our first partitioned list (matches predicate): " + partitioned_lists._1.size().string()) // 1
env.out.print("The size of our second partitioned list (doesn't match predicate): " + partitioned_lists._2.size().string()) // 1
env.out.print("Our matching partition elements are:")
for n in partitioned_lists._1.values() do
env.out.print("\t" + n.string()) // Second BOOM!
end
class ref List[A: A] is Seq[A] ref
Implements
- Seq[A] ref
Constructors
create
Do nothing, but be compatible with Seq.
new ref create( len: USize val = 0) : List[A] ref^
Parameters
- len: USize val = 0
Returns
- List[A] ref^
unit
Builds a new list from an element.
new ref unit( a: A) : List[A] ref^
Parameters
- a: A
Returns
- List[A] ref^
from
Builds a new list from the sequence passed in.
new ref from( seq: Array[A^] ref) : List[A] ref^
Parameters
- seq: Array[A^] ref
Returns
- List[A] ref^
Public Functions
reserve
Do nothing, but be compatible with Seq.
fun ref reserve( len: USize val) : None val
Parameters
- len: USize val
Returns
- None val
size
Returns the number of items in the list.
fun box size() : USize val
Returns
- USize val
apply
Get the i-th element, raising an error if the index is out of bounds.
fun box apply( i: USize val = 0) : this->A ?
Parameters
- i: USize val = 0
Returns
- this->A ?
update
Change the i-th element, raising an error if the index is out of bounds. Returns the previous value, which may be None if the node has been popped but left on the list.
fun ref update( i: USize val, value: A) : A^ ?
Parameters
- i: USize val
- value: A
Returns
- A^ ?
index
Gets the i-th node, raising an error if the index is out of bounds.
fun box index( i: USize val) : this->ListNode[A] ref ?
Parameters
- i: USize val
Returns
- this->ListNode[A] ref ?
remove
Remove the i-th node, raising an error if the index is out of bounds. The removed node is returned.
fun ref remove( i: USize val) : ListNode[A] ref ?
Parameters
- i: USize val
Returns
- ListNode[A] ref ?
clear
Empties the list.
fun ref clear() : None val
Returns
- None val
head
Get the head of the list.
fun box head() : this->ListNode[A] ref ?
Returns
- this->ListNode[A] ref ?
tail
Get the tail of the list.
fun box tail() : this->ListNode[A] ref ?
Returns
- this->ListNode[A] ref ?
prepend_node
Adds a node to the head of the list.
fun ref prepend_node( node: ListNode[A] ref) : None val
Parameters
- node: ListNode[A] ref
Returns
- None val
append_node
Adds a node to the tail of the list.
fun ref append_node( node: ListNode[A] ref) : None val
Parameters
- node: ListNode[A] ref
Returns
- None val
append_list
Remove all nodes from that and append them to this.
fun ref append_list( that: List[A] ref) : None val
Parameters
- that: List[A] ref
Returns
- None val
prepend_list
Remove all nodes from that and prepend them to this.
fun ref prepend_list( that: List[A] ref) : None val
Parameters
- that: List[A] ref
Returns
- None val
push
Adds a value to the tail of the list.
fun ref push( a: A) : None val
Parameters
- a: A
Returns
- None val
pop
Removes a value from the tail of the list.
fun ref pop() : A^ ?
Returns
- A^ ?
unshift
Adds a value to the head of the list.
fun ref unshift( a: A) : None val
Parameters
- a: A
Returns
- None val
shift
Removes a value from the head of the list.
fun ref shift() : A^ ?
Returns
- A^ ?
append
Append len elements from a sequence, starting from the given offset.
fun ref append( seq: (ReadSeq[A] box & ReadElement[A^] box), offset: USize val = 0, len: USize val = call) : None val
Parameters
- seq: (ReadSeq[A] box & ReadElement[A^] box)
- offset: USize val = 0
- len: USize val = call
Returns
- None val
concat
Add len iterated elements to the end of the list, starting from the given offset.
fun ref concat( iter: Iterator[A^] ref, offset: USize val = 0, len: USize val = call) : None val
Parameters
Returns
- None val
truncate
Truncate the list to the given length, discarding excess elements. If the list is already smaller than len, do nothing.
fun ref truncate( len: USize val) : None val
Parameters
- len: USize val
Returns
- None val
clone
Clone the list.
fun box clone() : List[this->A!] ref^
Returns
- List[this->A!] ref^
map[B: B]
Builds a new list by applying a function to every member of the list.
fun box map[B: B](
f: {(this->A!): B^}[A, B] box)
: List[B] ref^
Parameters
- f: {(this->A!): B^}[A, B] box
Returns
- List[B] ref^
flat_map[B: B]
Builds a new list by applying a function to every member of the list and using the elements of the resulting lists.
fun box flat_map[B: B](
f: {(this->A!): List[B]}[A, B] box)
: List[B] ref^
Parameters
- f: {(this->A!): List[B]}[A, B] box
Returns
- List[B] ref^
filter
Builds a new list with those elements that satisfy a provided predicate.
fun box filter(
f: {(this->A!): Bool}[A] box)
: List[this->A!] ref^
Parameters
- f: {(this->A!): Bool}[A] box
Returns
- List[this->A!] ref^
fold[B: B]
Folds the elements of the list using the supplied function.
fun box fold[B: B](
f: {(B!, this->A!): B^}[A, B] box,
acc: B)
: B
Parameters
- f: {(B!, this->A!): B^}[A, B] box
- acc: B
Returns
- B
every
Returns true if every element satisfies the provided predicate, false otherwise.
fun box every(
f: {(this->A!): Bool}[A] box)
: Bool val
Parameters
- f: {(this->A!): Bool}[A] box
Returns
- Bool val
exists
Returns true if at least one element satisfies the provided predicate, false otherwise.
fun box exists(
f: {(this->A!): Bool}[A] box)
: Bool val
Parameters
- f: {(this->A!): Bool}[A] box
Returns
- Bool val
partition
Builds a pair of lists, the first of which is made up of the elements satisfying the supplied predicate and the second of which is made up of those that do not.
fun box partition(
f: {(this->A!): Bool}[A] box)
: (List[this->A!] ref^ , List[this->A!] ref^)
Parameters
- f: {(this->A!): Bool}[A] box
Returns
drop
Builds a list by dropping the first n elements.
fun box drop( n: USize val) : List[this->A!] ref^
Parameters
- n: USize val
Returns
- List[this->A!] ref^
take
Builds a list of the first n elements.
fun box take( n: USize val) : List[this->A!] ref
Parameters
- n: USize val
Returns
- List[this->A!] ref
take_while
Builds a list of elements satisfying the provided predicate until one does not.
fun box take_while(
f: {(this->A!): Bool}[A] box)
: List[this->A!] ref^
Parameters
- f: {(this->A!): Bool}[A] box
Returns
- List[this->A!] ref^
reverse
Builds a new list by reversing the elements in the list.
fun box reverse() : List[this->A!] ref^
Returns
- List[this->A!] ref^
contains[optional B: (A & HasEq[A!] #read)]
Returns true if the list contains the provided element, false otherwise.
fun box contains[optional B: (A & HasEq[A!] #read)]( a: box->B) : Bool val
Parameters
- a: box->B
Returns
- Bool val
nodes
Return an iterator on the nodes in the list.
fun box nodes() : ListNodes[A, this->ListNode[A] ref] ref^
Returns
rnodes
Return an iterator on the nodes in the list.
fun box rnodes() : ListNodes[A, this->ListNode[A] ref] ref^
Returns
values
Return an iterator on the values in the list.
fun box values() : ListValues[A, this->ListNode[A] ref] ref^
Returns
- ListValues[A, this->ListNode[A] ref] ref^
rvalues
Return an iterator on the values in the list.
fun box rvalues() : ListValues[A, this->ListNode[A] ref] ref^
Returns
- ListValues[A, this->ListNode[A] ref] ref^
© 2016-2020, The Pony Developers
© 2014-2015, Causality Ltd.
Licensed under the BSD 2-Clause License.
https://stdlib.ponylang.io/collections-List
