feat: Moves core functionality into it's own library.

Sources/CliDocCore/Nodes/AnyTextNode.swift

@@ -0,0 +1,21 @@
+/// A type-erased text node.
+public struct AnyTextNode: TextNode {
+  @usableFromInline
+  let makeString: () -> String
+
+  @inlinable
+  public init<N: TextNode>(_ node: N) {
+    self.makeString = node.render
+  }
+
+  @inlinable
+  public var body: some TextNode { makeString() }
+}
+
+public extension TextNode {
+
+  @inlinable
+  func eraseToAnyTextNode() -> AnyTextNode {
+    AnyTextNode(self)
+  }
+}

Sources/CliDocCore/Nodes/Empty.swift

@@ -0,0 +1,11 @@
+/// An empty text node.
+public struct Empty: TextNode {
+
+  @inlinable
+  public init() {}
+
+  @inlinable
+  public var body: some TextNode {
+    ""
+  }
+}

Sources/CliDocCore/Nodes/Group.swift

@@ -0,0 +1,16 @@
+public struct Group<Content: TextNode>: TextNode {
+  @usableFromInline
+  var content: Content
+
+  @inlinable
+  public init(
+    @TextBuilder content: () -> Content
+  ) {
+    self.content = content()
+  }
+
+  @inlinable
+  public var body: some TextNode {
+    content
+  }
+}

Sources/CliDocCore/Nodes/HStack.swift

@@ -0,0 +1,23 @@
+public struct HStack: TextNode {
+
+  @usableFromInline
+  let content: [any TextNode]
+
+  @usableFromInline
+  let separator: any TextNode
+
+  @inlinable
+  public init(
+    spacing: Int = 1,
+    @TextBuilder content: () -> any TextNode
+  ) {
+    self.content = array(from: content())
+    self.separator = seperator(" ", count: spacing > 0 ? spacing - 1 : 0)
+  }
+
+  @inlinable
+  public var body: some TextNode {
+    content.removingEmptys()
+      .joined(separator: separator.render())
+  }
+}

Sources/CliDocCore/Nodes/Section.swift

@@ -0,0 +1,96 @@
+// TODO: Add vertical spacing.
+public struct Section<Header: TextNode, Content: TextNode, Footer: TextNode>: TextNode {
+
+  @usableFromInline
+  let header: Header
+
+  @usableFromInline
+  let content: Content
+
+  @usableFromInline
+  let footer: Footer
+
+  @inlinable
+  public init(
+    @TextBuilder content: () -> Content,
+    @TextBuilder header: () -> Header,
+    @TextBuilder footer: () -> Footer
+  ) {
+    self.header = header()
+    self.content = content()
+    self.footer = footer()
+  }
+
+  public var body: some TextNode {
+    style(.default)
+  }
+}
+
+public extension Section where Footer == Empty {
+  @inlinable
+  init(
+    @TextBuilder content: () -> Content,
+    @TextBuilder header: () -> Header
+  ) {
+    self.init(content: content, header: header) { Empty() }
+  }
+}
+
+public extension Section where Header == Empty {
+  @inlinable
+  init(
+    @TextBuilder content: () -> Content,
+    @TextBuilder footer: () -> Footer
+  ) {
+    self.init(content: content, header: { Empty() }, footer: footer)
+  }
+}
+
+public extension Section where Header == Empty, Footer == Empty {
+  @inlinable
+  init(
+    @TextBuilder content: () -> Content
+  ) {
+    self.init(content: content, header: { Empty() }, footer: { Empty() })
+  }
+}
+
+// MARK: - Style
+
+public extension Section {
+
+  @inlinable
+  func style<S: SectionStyle>(_ style: S) -> some TextNode {
+    style.render(content: .init(header: header, content: content, footer: footer))
+  }
+}
+
+public struct SectionConfiguration {
+  public let header: any TextNode
+  public let content: any TextNode
+  public let footer: any TextNode
+
+  @usableFromInline
+  init(header: any TextNode, content: any TextNode, footer: any TextNode) {
+    self.header = header
+    self.content = content
+    self.footer = footer
+  }
+}
+
+public protocol SectionStyle: NodeModifier where Content == SectionConfiguration {}
+
+public extension SectionStyle where Self == DefaultSectionStyle {
+  static var `default`: Self { DefaultSectionStyle() }
+}
+
+public struct DefaultSectionStyle: SectionStyle {
+
+  public func render(content: SectionConfiguration) -> some TextNode {
+    VStack(spacing: 2) {
+      content.header
+      content.content
+      content.footer
+    }
+  }
+}

Sources/CliDocCore/Nodes/VStack.swift

@@ -0,0 +1,23 @@
+public struct VStack: TextNode {
+
+  @usableFromInline
+  let content: [any TextNode]
+
+  @usableFromInline
+  let separator: any TextNode
+
+  @inlinable
+  public init(
+    spacing: Int = 1,
+    @TextBuilder content: () -> any TextNode
+  ) {
+    self.content = array(from: content())
+    self.separator = seperator("\n", count: spacing > 0 ? spacing - 1 : 0)
+  }
+
+  @inlinable
+  public var body: some TextNode {
+    content.removingEmptys()
+      .joined(separator: separator.render())
+  }
+}