Initial implementation of channel overscroll navigation

submodules/ComponentFlow/Source/Components/List.swift

@@ -0,0 +1,48 @@
+import Foundation
+import UIKit
+
+public final class List<ChildEnvironment: Equatable>: CombinedComponent {
+    public typealias EnvironmentType = ChildEnvironment
+
+    private let items: [AnyComponentWithIdentity<ChildEnvironment>]
+    private let appear: Transition.Appear
+
+    public init(_ items: [AnyComponentWithIdentity<ChildEnvironment>], appear: Transition.Appear = .default()) {
+        self.items = items
+        self.appear = appear
+    }
+
+    public static func ==(lhs: List<ChildEnvironment>, rhs: List<ChildEnvironment>) -> Bool {
+        if lhs.items != rhs.items {
+            return false
+        }
+        return true
+    }
+
+    public static var body: Body {
+        let children = ChildMap(environment: ChildEnvironment.self, keyedBy: AnyHashable.self)
+
+        return { context in
+            let updatedChildren = context.component.items.map { item in
+                return children[item.id].update(
+                    component: item.component, environment: {
+                        context.environment[ChildEnvironment.self]
+                    },
+                    availableSize: context.availableSize,
+                    transition: context.transition
+                )
+            }
+
+            var nextOrigin: CGFloat = 0.0
+            for child in updatedChildren {
+                context.add(child
+                    .position(CGPoint(x: child.size.width / 2.0, y: nextOrigin + child.size.height / 2.0))
+                    .appear(context.component.appear)
+                )
+                nextOrigin += child.size.height
+            }
+
+            return context.availableSize
+        }
+    }
+}