Add LSEQ

Package.swift

@@ -46,5 +46,13 @@ let package = Package(
             name: "CRDTRegistersTests",
             dependencies: ["CRDTRegisters"]
         ),
+        .target(
+            name: "LSEQ",
+            dependencies: []
+        ),
+        .testTarget(
+            name: "LSEQTests",
+            dependencies: ["LSEQ"]
+        ),
     ]
 )

README.md

@@ -68,6 +68,13 @@ See the tests for more examples.
 
 ## Related Links
 
+### CRDT Papers
+
+* [Convergent and Commutative Replicated Data Types][crdt]
+* [LSEQ, an Adaptive Structure for Sequences in Distributed Collaborative Editing][lseq]
+
+### Other Projects
+
 See other projects which have implementations for CRDTs:
 
 * [rust-crdt][rust_crdt]
@@ -82,3 +89,4 @@ See other projects which have implementations for CRDTs:
 [crdt]: https://hal.inria.fr/file/index/docid/555588/filename/techreport.pdf
 [rust_crdt]: https://github.com/rust-crdt/rust-crdt
 [java_crdt]: https://github.com/ajantis/java-crdt
+[lseq]: https://hal.archives-ouvertes.fr/hal-00921633/document

Sources/LSEQ/LSEQ.swift

@@ -0,0 +1,84 @@
+//  Copyright 2019 Bryant Luk
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+
+public protocol LSEQ: Collection {
+    associatedtype PositionType
+
+    associatedtype Element
+
+    associatedtype Index
+
+    associatedtype ElementContainer where ElementContainer: LSEQElementContainer,
+        ElementContainer.PositionType == PositionType, ElementContainer.Element == Element
+
+    associatedtype Operation where Operation: LSEQOperation,
+        Operation.PositionType == PositionType, Operation.Element == Element
+
+    var boundary: PositionType.Segment.Identifier { get }
+    var source: PositionType.Segment.Source { get }
+    var startPosition: PositionType { get }
+    var endPosition: PositionType { get }
+    var clock: PositionType.Clock { get }
+    var storage: [ElementContainer] { get }
+
+    mutating func reserveCapacity(_ minimumCapacity: Int)
+
+    mutating func insert(_ newElement: Element, at index: Index)
+
+    mutating func insertAndMakeOperation(_ newElement: Element, at index: Index) -> Operation
+
+    @discardableResult
+    mutating func remove(at index: Index) -> Element
+
+    @discardableResult
+    mutating func removeAndMakeOperation(at index: Index) -> (Element, Operation)
+
+    mutating func apply(_ operation: Operation)
+
+    func makeDifferenceOperations(from other: Self) -> [Operation]
+}
+
+public protocol LSEQOperation {
+    associatedtype Kind
+    associatedtype PositionType where PositionType: Position
+    associatedtype Element
+
+    var kind: Kind { get }
+    var position: PositionType { get }
+    var element: Element? { get }
+}
+
+public protocol LSEQElementContainer {
+    associatedtype PositionType where PositionType: Position
+    associatedtype Element
+
+    var position: PositionType { get }
+    var element: Element { get }
+}
+
+internal extension RandomAccessCollection {
+    func insertionIndex(for predicate: (Element) -> Bool) -> Index {
+        var slice: SubSequence = self[...]
+
+        while !slice.isEmpty {
+            let middle = slice.index(slice.startIndex, offsetBy: slice.count / 2)
+            if predicate(slice[middle]) {
+                slice = slice[index(after: middle)...]
+            } else {
+                slice = slice[..<middle]
+            }
+        }
+        return slice.startIndex
+    }
+}