Implement delays for show() and switch()

src/branch.luau

@@ -0,0 +1,40 @@
+local graph = require "./graph"
+type Node<T> = graph.Node<T>
+local create_node = graph.create_node
+local push_scope = graph.push_scope
+local pop_scope = graph.pop_scope
+local destroy = graph.destroy
+local get_scope = graph.get_scope
+
+local function branch<T>(fn: () -> T): (() -> (), T)
+    local current = get_scope()
+    if not current then
+        error(`cannot use branch() outside a stable or reactive scope`, 0)
+    end
+
+    local parent = current.owner
+    if not parent or parent.effect then
+        error(`current scope is not owned by a stable scope`, 0)
+    end
+
+    local node = create_node(parent, false, false)
+
+    local destroy = function()
+        destroy(node)
+    end
+
+    push_scope(node)
+
+    local ok, result = xpcall(fn, debug.traceback)
+
+    pop_scope()
+
+    if not ok then
+        destroy()
+        error(`error while running branch():\n\n{result}`, 0)
+    end
+
+    return destroy, result
+end
+
+return branch