Added support for DOM walking using a visitor

Changelog.md

@@ -18,6 +18,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Added support for the visitor pattern,
+  by adding `protocol Visitor`/`protocol Visitable` & `enum VisitorContinueKind`.
 - Added a changelog.
   #17 by @mattt.
 

Sources/CommonMark/Supporting Types/Children.swift

@@ -52,7 +52,9 @@ fileprivate func add<Child: Node>(_ child: Child, with operation: () -> Int32) -
 
 // MARK: -
 
-public protocol ContainerOfBlocks: Node {}
+public protocol ContainerOfBlocks: Node {
+    var children: [Block & Node] { get }
+}
 
 extension Document: ContainerOfBlocks {}
 extension BlockQuote: ContainerOfBlocks {}
@@ -166,7 +168,9 @@ extension ContainerOfBlocks {
 
 // MARK: -
 
-public protocol ContainerOfInlineElements: Node {}
+public protocol ContainerOfInlineElements: Node {
+    var children: [Inline & Node] { get }
+}
 
 extension Heading: ContainerOfInlineElements {}
 extension Paragraph: ContainerOfInlineElements {}

Sources/CommonMark/Supporting Types/Visitable.swift

@@ -0,0 +1,229 @@
+public protocol Visitable {
+    func accept<T: Visitor>(visitor: T)
+}
+
+// MARK: - Document
+
+extension Document: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(document: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(document: self)
+    }
+}
+
+// MARK: - Container Blocks
+
+extension BlockQuote: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(blockQuote: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(blockQuote: self)
+    }
+}
+
+extension List: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(list: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(list: self)
+    }
+}
+
+extension List.Item: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(listItem: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(listItem: self)
+    }
+}
+
+// MARK: - Leaf Blocks
+
+extension Heading: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(heading: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(heading: self)
+    }
+}
+
+extension Paragraph: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(paragraph: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(paragraph: self)
+    }
+}
+
+extension HTMLBlock: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(htmlBlock: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(htmlBlock: self)
+    }
+}
+
+extension CodeBlock: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(codeBlock: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(codeBlock: self)
+    }
+}
+
+extension ThematicBreak: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(thematicBreak: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(thematicBreak: self)
+    }
+}
+
+// MARK: - Inline
+
+extension Text: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(text: self))
+        visitor.visitPost(text: self)
+    }
+}
+
+extension Strong: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(strong: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(strong: self)
+    }
+}
+
+extension Emphasis: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(emphasis: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(emphasis: self)
+    }
+}
+
+extension Link: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        let continueKind = visitor.visit(self, by: visitor.visit(link: self))
+        if continueKind == .visitChildren {
+            self.walkVisitableChildren(with: visitor)
+        }
+        visitor.visitPost(link: self)
+    }
+}
+
+extension Image: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(image: self))
+        visitor.visitPost(image: self)
+    }
+}
+
+extension Code: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(code: self))
+        visitor.visitPost(code: self)
+    }
+}
+
+extension RawHTML: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(rawHTML: self))
+        visitor.visitPost(rawHTML: self)
+    }
+}
+
+extension SoftLineBreak: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(softLineBreak: self))
+        visitor.visitPost(softLineBreak: self)
+    }
+}
+
+extension HardLineBreak: Visitable {
+    public func accept<T: Visitor>(visitor: T) {
+        _ = visitor.visit(self, by: visitor.visit(hardLineBreak: self))
+        visitor.visitPost(hardLineBreak: self)
+    }
+}
+
+// MARK: - Convenience Helpers
+
+extension ContainerOfBlocks {
+    internal var visitableChildren: AnyCollection<Visitable & Block & Node> {
+        return AnyCollection(self.children.lazy.compactMap {
+            $0 as? Visitable & Block & Node
+        })
+    }
+
+    internal func walkVisitableChildren<T: Visitor>(with visitor: T) {
+        for child in self.visitableChildren {
+            child.accept(visitor: visitor)
+        }
+    }
+}
+
+extension ContainerOfInlineElements {
+    internal var visitableChildren: AnyCollection<Visitable & Inline & Node> {
+        return AnyCollection(self.children.lazy.compactMap {
+            $0 as? Visitable & Inline & Node
+        })
+    }
+
+    internal func walkVisitableChildren<T: Visitor>(with visitor: T) {
+        for child in self.visitableChildren {
+            child.accept(visitor: visitor)
+        }
+    }
+}
+
+extension List {
+    internal var visitableChildren: AnyCollection<Visitable & List.Item> {
+        return AnyCollection(self.children)
+    }
+
+    internal func walkVisitableChildren<T: Visitor>(with visitor: T) {
+        for child in self.visitableChildren {
+            child.accept(visitor: visitor)
+        }
+    }
+}
+
+extension List.Item {
+    internal var visitableChildren: AnyCollection<Visitable & Node> {
+        return AnyCollection(self.children.lazy.compactMap {
+            $0 as? Visitable & Node
+        })
+    }
+
+    internal func walkVisitableChildren<T: Visitor>(with visitor: T) {
+        for child in self.visitableChildren {
+            child.accept(visitor: visitor)
+        }
+    }
+}