Finish sub-page documentation updates (#204)

* Finish sub-page documentation updates

Some of these pages could use introductions, but the current state is
ready for publication.

* Add SPI yaml file for building docs

.spi.yml

@@ -0,0 +1,5 @@
+version: 1
+builder:
+  configs:
+    - documentation_targets: [Algorithms]
+

Sources/Algorithms/Chunked.swift

@@ -777,8 +777,8 @@ extension ChunksOfCountCollection {
 }
 
 extension Collection {
-  /// Returns a collection of subsequences of this collection, each with the
-  /// specified length.
+  /// Returns a collection of subsequences, each with up to the specified
+  /// length.
   ///
   /// If the number of elements in the collection is evenly divided by `count`,
   /// then every chunk will have a length equal to `count`. Otherwise, every
@@ -792,8 +792,7 @@ extension Collection {
   ///     // [1, 2, 3, 4, 5]
   ///     // [6, 7, 8, 9, 10]
   ///
-  ///     print(c.chunks(ofCount: 3).map(Array.init))
-  ///     for chunk in numbers.chunks(ofCount: 5) {
+  ///     for chunk in numbers.chunks(ofCount: 3) {
   ///         print(chunk)
   ///     }
   ///     // [1, 2, 3]
@@ -808,6 +807,7 @@ extension Collection {
   ///
   /// - Complexity: O(1) if the collection conforms to `RandomAccessCollection`;
   ///   otherwise, O(*k*), where *k* is equal to `count`.
+  ///
   @inlinable
   public func chunks(ofCount count: Int) -> ChunksOfCountCollection<Self> {
     precondition(count > 0, "Cannot chunk with count <= 0!")
@@ -828,7 +828,8 @@ extension ChunksOfCountCollection: LazyCollectionProtocol
 //===----------------------------------------------------------------------===//
 
 extension Collection {
-  /// Returns a collection of evenly divided subsequences of this collection.
+  /// Returns a collection of evenly divided consecutive subsequences of this
+  /// collection.
   ///
   /// This method divides the collection into a given number of evenly sized
   /// chunks. If the length of the collection is not divisible by `count`, the

Sources/Algorithms/Documentation.docc/Algorithms.md

@@ -5,8 +5,25 @@ along with their related types.
 
 ## Overview
 
-This library adds a variety of extended operations to the Swift standard library's
-`Sequence` and `Collection` protocols, via extension methods and global functions.
+The Algorithms package provides a variety of sequence and collection operations, letting you cycle over a collection's elements, find combinations and permutations, create a random sample, and more.
+
+For example, the package includes a group of "chunking" methods, each of which breaks a collection into consecutive subsequences. One version tests adjacent elements to find the breaking point between chunks — you can use it to quickly separate an array into ascending runs:
+
+```swift
+let numbers = [10, 20, 30, 10, 40, 40, 10, 20]
+let chunks = numbers.chunked(by: { $0 <= $1 })
+// [[10, 20, 30], [10, 40, 40], [10, 20]]
+```
+
+Another version looks for a change in the transformation of each successive value. You can use that to separate a list of names into groups by the first character:
+
+```swift
+let names = ["Cassie", "Chloe", "Jasmine", "Jordan", "Taylor"]
+let chunks = names.chunked(on: \.first)
+// [["Cassie", "Chloe"], ["Jasmine", "Jordan"], ["Taylor"]]
+```
+
+Explore more chunking methods and the remainder of the Algorithms package, grouped in the following topics.
 
 ## Topics
 

Sources/Algorithms/Documentation.docc/Chunking.md

@@ -4,6 +4,17 @@ Break collections into consecutive chunks by length, count, or based on closure-
 
 ## Overview
 
+_Chunking_ is the process of breaking a collection into consecutive subsequences, without dropping or duplicating any of the collection's elements. After chunking a collection, joining the resulting subsequences produces the original collection of elements, unlike _splitting_, which consumes the separator element(s).
+
+```swift
+let names = ["Ji-sun", "Jin-su", "Min-jae", "Young-ho"]
+let evenlyChunked = names.chunks(ofCount: 2)
+// ~ [["Ji-sun", "Jin-su"], ["Min-jae", "Young-ho"]] 
+
+let chunkedByFirstLetter = names.chunked(on: \.first)
+// equivalent to [("J", ["Ji-sun", "Jin-su"]), ("M", ["Min-jae"]), ("Y", ["Young-ho"])]
+```
+
 ## Topics
 
 ### Chunking a Collection by Count
@@ -13,10 +24,12 @@ Break collections into consecutive chunks by length, count, or based on closure-
 
 ### Chunking a Collection by Predicate
 
-- ``Swift/Collection/chunked(on:)``
 - ``Swift/Collection/chunked(by:)``
 - ``Swift/LazySequenceProtocol/chunked(by:)``
-- ``Swift/LazySequenceProtocol/chunked(by:)``
+
+### Chunking a Collection by Subject
+
+- ``Swift/Collection/chunked(on:)``
 - ``Swift/LazySequenceProtocol/chunked(on:)``
 
 ### Supporting Types

Sources/Algorithms/Documentation.docc/DeprecatedScan.md

@@ -1,8 +1,8 @@
 # DeprecatedScan
 
-These methods are deprecated, use the `reductions` family of methods instead.
+These methods are deprecated; use the `reductions` family of methods instead.
 
-## Overview
+See: <doc:Reductions>
 
 ## Topics
 

Sources/Algorithms/Documentation.docc/Extending.md

@@ -3,6 +3,27 @@
 Chain two collections end-to-end,
 or repeat a collection forever or a specific number of times.    
 
+## Overview
+
+_Chaining_ two collections 
+
+```swift
+let letters = chain("abcd", "EFGH")
+// String(letters) == "abcdEFGH"
+
+for (num, letter) in zip((1...3).cycled(), letters) { 
+    print(num, letter)
+} 
+// 1 a
+// 2 b
+// 3 c
+// 1 d
+// 2 E
+// 3 F
+// 1 G
+// 2 H
+```
+
 ## Topics
 
 ### Chaining Two Collections

Sources/Algorithms/Documentation.docc/Filtering.md

@@ -4,17 +4,32 @@ Remove duplicated elements or strip the `nil` values from a sequence or collecti
 
 ## Overview
 
-<!--@START_MENU_TOKEN@-->Text<!--@END_MENU_TOKEN@-->
+Use the _uniquing_ methods to remove duplicates from a sequence or collection, or to remove elements that have a duplicated property. 
+
+```swift
+let numbers = [1, 2, 3, 3, 2, 3, 3, 2, 2, 2, 1]
+
+let unique = numbers.uniqued()
+// Array(unique) == [1, 2, 3]
+```
+
+The `compacted()` method removes all `nil` values from a sequence or collection of optionals: 
+
+```swift
+let array: [Int?] = [10, nil, 30, nil, 2, 3, nil, 5]
+let withNoNils = array.compacted()
+// Array(withNoNils) == [10, 30, 2, 3, 5]
+```
 
 ## Topics
 
-### Uniqueing Elements
+### Uniquing Elements
 
 - ``Swift/Sequence/uniqued()``
 - ``Swift/Sequence/uniqued(on:)``
 - ``Swift/LazySequenceProtocol/uniqued(on:)``
 
-### Filtering out nil Elements
+### Filtering out `nil` Elements
 
 - ``Swift/Collection/compacted()``
 - ``Swift/Sequence/compacted()``

Sources/Algorithms/Documentation.docc/Partitioning.md

@@ -4,6 +4,35 @@ Partition a collection according to a unary predicate,
 rotate a collection around a particular index,
 or find the index where a collection is already partitioned.
 
+## Overview
+
+A _stable partition_ maintains the relative order of elements within both partitions.
+
+```swift
+// partition(by:) - unstable ordering
+var numbers = [10, 20, 30, 40, 50, 60, 70, 80]
+let p1 = numbers.partition(by: { $0.isMultiple(of: 20) })
+// p1 == 4
+// numbers == [10, 70, 30, 50, 40, 60, 20, 80]
+//                             ^ start of second partition
+
+// stablePartition(by:) - maintains relative ordering
+numbers = [10, 20, 30, 40, 50, 60, 70, 80]
+let p2 = numbers.stablePartition(by: { $0.isMultiple(of: 20) })
+// p2 == 4
+// numbers == [10, 30, 50, 70, 20, 40, 60, 80]
+//                             ^ start of second partition
+```
+
+Use the `rotate` method to shift the elements of a collection to start at a new position, moving the displaced elements to the end: 
+
+```swift
+var numbers = [10, 20, 30, 40, 50, 60, 70, 80]
+let p = numbers.rotate(toStartAt: 2)
+// numbers == [30, 40, 50, 60, 70, 80, 10, 20]
+// p == 6 -- numbers[p] == 10
+```
+
 ## Topics
 
 ### Stable Partition

Sources/Algorithms/Documentation.docc/Reductions.md

@@ -2,6 +2,20 @@
 
 Find the incremental values of a sequence "reduce" operation.
 
+## Overview
+
+Call one of the `reductions` methods when you want the result of a `reduce` operation along with all of its intermediate values: 
+
+```swift
+let exclusiveRunningTotal = (1...5).reductions(0, +)
+print(exclusiveRunningTotal)
+// prints [0, 1, 3, 6, 10, 15]
+
+let inclusiveRunningTotal = (1...5).reductions(+)
+print(inclusiveRunningTotal)
+// prints [1, 3, 6, 10, 15]
+```
+
 ## Topics
 
 - ``Swift/Sequence/reductions(_:)``

Sources/Algorithms/Documentation.docc/SlicingSplitting.md

@@ -15,8 +15,6 @@ Iterate over tuple pairs of adjacent elements, overlapping windows of a specifie
 
 ### Lazily Splitting a Collection
 
-These methods…
-
 - ``Swift/LazySequenceProtocol/split(separator:maxSplits:omittingEmptySubsequences:)-4q4x8``
 - ``Swift/LazySequenceProtocol/split(maxSplits:omittingEmptySubsequences:whereSeparator:)-68oqf``
 - ``Swift/LazySequenceProtocol/split(separator:maxSplits:omittingEmptySubsequences:)-a46s``