Merge reactive scope refactor

src/effect.luau

@@ -0,0 +1,22 @@
+if not game then script = require "test/relative-string" end
+
+local throw = require(script.Parent.throw)
+local graph = require(script.Parent.graph)
+local create_node = graph.create_node
+local get_scope = graph.get_scope
+local evaluate_node = graph.evaluate_node
+local set_owner = graph.set_owner
+
+local function effect<T>(callback: (T) -> T, initial_value: T)
+    local owner = get_scope()
+    if not owner then
+        throw("cannot create effect in non-reactive scope")
+    end; assert(owner)
+
+    local node = create_node(initial_value, callback)
+
+    set_owner(node, owner)
+    evaluate_node(node)
+end
+
+return effect :: (<T>(callback: (T) -> T, initial_value: T) -> ()) & ((callback: () -> ()) -> ())