diff --git a/crates/graph/src/builder.rs b/crates/graph/src/builder.rs
new file mode 100644
index 0000000..68b85c9
--- /dev/null
+++ b/crates/graph/src/builder.rs
@@ -0,0 +1,153 @@
+use crate::node::{AsyncRuleNode, ConstNode, Node, RuleNode};
+use crate::util;
+use crate::{
+    AsyncRule, Asynchronous, ErasedNode, Graph, Input, InvalidationSignal, NodeGraph, NodeId, Rule,
+    Synchronicity, Synchronous,
+};
+use std::cell::{Cell, RefCell};
+use std::rc::Rc;
+
+pub struct GraphBuilder<Output, Synch: Synchronicity> {
+    pub(crate) node_graph: Rc<RefCell<NodeGraph<Synch>>>,
+    pub(crate) output: Option<Input<Output>>,
+    pub(crate) output_type: std::marker::PhantomData<Output>,
+}
+
+impl<O: 'static> GraphBuilder<O, Synchronous> {
+    pub fn new() -> Self {
+        Self {
+            node_graph: Rc::new(RefCell::new(NodeGraph::new())),
+            output: None,
+            output_type: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<O: 'static> GraphBuilder<O, Asynchronous> {
+    pub fn new_async() -> Self {
+        Self {
+            node_graph: Rc::new(RefCell::new(NodeGraph::new())),
+            output: None,
+            output_type: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<O: 'static, S: Synchronicity> GraphBuilder<O, S> {
+    pub fn set_output<R: Rule<Output = O>>(&mut self, rule: R) {
+        let input = self.add_rule(rule);
+        self.output = Some(input);
+    }
+
+    fn add_node<V: 'static>(&mut self, node: impl Node<V, S> + 'static) -> Input<V> {
+        let value = Rc::clone(node.value_rc());
+        let erased = ErasedNode::new(node);
+        let idx = self.node_graph.borrow_mut().add_node(erased);
+        Input {
+            node_idx: idx,
+            value,
+        }
+    }
+
+    pub fn add_value<V: 'static>(&mut self, value: V) -> Input<V> {
+        return self.add_node(ConstNode::new(value));
+    }
+
+    pub fn add_rule<R>(&mut self, rule: R) -> Input<R::Output>
+    where
+        R: Rule,
+    {
+        return self.add_node(RuleNode::new(rule));
+    }
+
+    pub fn add_invalidatable_rule<R, F>(&mut self, mut f: F) -> Input<R::Output>
+    where
+        R: Rule,
+        F: FnMut(InvalidationSignal<S>) -> R,
+    {
+        let node_idx = Rc::new(Cell::new(None));
+        let signal = InvalidationSignal {
+            node_idx: Rc::clone(&node_idx),
+            graph: Rc::clone(&self.node_graph),
+        };
+        let input = self.add_rule(f(signal));
+        node_idx.set(Some(input.node_idx));
+        input
+    }
+
+    pub fn build(self) -> Result<Graph<O, S>, BuildGraphError> {
+        let output: &Input<O> = match &self.output {
+            None => return Err(BuildGraphError::NoOutput),
+            Some(output) => output,
+        };
+
+        let graph = self.node_graph.borrow();
+        let indices = graph.node_indices().collect::<Vec<_>>();
+        drop(graph);
+        let mut edges = vec![];
+        for idx in indices {
+            let node = &mut self.node_graph.borrow_mut()[idx];
+            node.visit_inputs(&mut |input_idx| {
+                edges.push((input_idx, idx));
+            });
+        }
+
+        for (source, dest) in edges {
+            self.node_graph.borrow_mut().add_edge(source, dest, ());
+        }
+
+        let mut graph = self.node_graph.borrow_mut();
+        util::remove_nodes_not_connected_to(&mut *graph, output.node_idx);
+        drop(graph);
+
+        let sorted = petgraph::algo::toposort(&**self.node_graph.borrow(), None);
+        if let Err(_cycle) = sorted {
+            self.node_graph.borrow_mut().clear_edges();
+            // TODO: actually build a vec describing the cycle path for debugging
+            return Err(BuildGraphError::Cyclic(vec![]));
+        }
+
+        let graph = Graph {
+            node_graph: self.node_graph,
+            output: self.output.unwrap(),
+            output_type: std::marker::PhantomData,
+        };
+
+        Ok(graph)
+    }
+}
+
+impl<O: 'static> GraphBuilder<O, Asynchronous> {
+    pub fn set_async_output<R: AsyncRule<Output = O>>(&mut self, rule: R) {
+        let input = self.add_async_rule(rule);
+        self.output = Some(input);
+    }
+
+    pub fn add_async_rule<R>(&mut self, rule: R) -> Input<R::Output>
+    where
+        R: AsyncRule,
+    {
+        self.add_node(AsyncRuleNode::new(rule))
+    }
+
+    pub fn add_invalidatable_async_rule<R, F>(&mut self, mut f: F) -> Input<R::Output>
+    where
+        R: AsyncRule,
+        F: FnMut(InvalidationSignal<Asynchronous>) -> R,
+    {
+        let node_idx = Rc::new(Cell::new(None));
+        let signal = InvalidationSignal {
+            node_idx: Rc::clone(&node_idx),
+            graph: Rc::clone(&self.node_graph),
+        };
+        let input = self.add_async_rule(f(signal));
+        node_idx.set(Some(input.node_idx));
+        input
+    }
+}
+
+#[derive(Debug)]
+pub enum BuildGraphError {
+    NoOutput,
+    Cyclic(Vec<NodeId>),
+}
diff --git a/crates/graph/src/lib.rs b/crates/graph/src/lib.rs
index b9e22bc..2e95231 100644
--- a/crates/graph/src/lib.rs
+++ b/crates/graph/src/lib.rs
@@ -1,18 +1,28 @@
+mod builder;
+mod node;
+mod synchronicity;
 mod util;
 
+use builder::{BuildGraphError, GraphBuilder};
+use node::ErasedNode;
 use petgraph::visit::{IntoEdgeReferences, NodeIndexable};
-use petgraph::{graph::NodeIndex, stable_graph::StableDiGraph, visit::EdgeRef};
-use std::any::Any;
+use petgraph::{stable_graph::StableDiGraph, visit::EdgeRef};
 use std::cell::{Cell, Ref, RefCell};
 use std::collections::HashMap;
 use std::collections::VecDeque;
-use std::future::Future;
 use std::ops::{Deref, DerefMut};
-use std::pin::Pin;
 use std::rc::Rc;
+use synchronicity::*;
 
 // use a struct for this, not a type alias, because generic bounds of type aliases aren't enforced
 struct NodeGraph<S: Synchronicity>(StableDiGraph<ErasedNode<S>, (), u32>);
+type NodeId = petgraph::stable_graph::NodeIndex<u32>;
+
+impl<S: Synchronicity> NodeGraph<S> {
+    fn new() -> Self {
+        Self(StableDiGraph::new())
+    }
+}
 
 impl<S: Synchronicity> Deref for NodeGraph<S> {
     type Target = StableDiGraph<ErasedNode<S>, (), u32>;
@@ -28,200 +38,6 @@ impl<S: Synchronicity> DerefMut for NodeGraph<S> {
     }
 }
 
-pub trait Synchronicity: 'static {
-    type UpdateFn;
-    fn make_update_fn<V: 'static>() -> Self::UpdateFn;
-
-    type UpdateResult<'a>;
-    fn make_update_result<'a>() -> Self::UpdateResult<'a>;
-}
-
-pub struct Synchronous;
-
-impl Synchronicity for Synchronous {
-    type UpdateFn = Box<dyn Fn(&mut Box<dyn Any>) -> ()>;
-
-    fn make_update_fn<V: 'static>() -> Self::UpdateFn {
-        Box::new(|any| {
-            let x = any.downcast_mut::<Box<dyn Node<V, Self>>>().unwrap();
-            x.update();
-        })
-    }
-
-    type UpdateResult<'a> = ();
-
-    fn make_update_result<'a>() -> Self::UpdateResult<'a> {}
-}
-
-pub struct Asynchronous;
-
-impl Synchronicity for Asynchronous {
-    type UpdateFn =
-        Box<dyn for<'a> Fn(&'a mut Box<dyn Any>) -> Pin<Box<dyn Future<Output = ()> + 'a>>>;
-
-    fn make_update_fn<V: 'static>() -> Self::UpdateFn {
-        Box::new(|any| Box::pin(Asynchronous::do_async_update::<V>(any)))
-    }
-
-    type UpdateResult<'a> = Pin<Box<dyn Future<Output = ()> + 'a>>;
-
-    fn make_update_result<'a>() -> Self::UpdateResult<'a> {
-        Box::pin(std::future::ready(()))
-    }
-}
-
-impl Asynchronous {
-    async fn do_async_update<V: 'static>(any: &mut Box<dyn Any>) {
-        let x = any.downcast_mut::<Box<dyn Node<V, Self>>>().unwrap();
-        x.update().await;
-    }
-}
-
-pub struct GraphBuilder<Output, Synch: Synchronicity> {
-    node_graph: Rc<RefCell<NodeGraph<Synch>>>,
-    output: Option<Input<Output>>,
-    output_type: std::marker::PhantomData<Output>,
-}
-
-impl<O: 'static> GraphBuilder<O, Synchronous> {
-    pub fn new() -> Self {
-        Self {
-            node_graph: Rc::new(RefCell::new(NodeGraph(StableDiGraph::new()))),
-            output: None,
-            output_type: std::marker::PhantomData,
-        }
-    }
-}
-
-impl<O: 'static> GraphBuilder<O, Asynchronous> {
-    pub fn new_async() -> Self {
-        Self {
-            node_graph: Rc::new(RefCell::new(NodeGraph(StableDiGraph::new()))),
-            output: None,
-            output_type: std::marker::PhantomData,
-        }
-    }
-}
-
-impl<O: 'static, S: Synchronicity> GraphBuilder<O, S> {
-    pub fn set_output<R: Rule<Output = O>>(&mut self, rule: R) {
-        let input = self.add_rule(rule);
-        self.output = Some(input);
-    }
-
-    fn add_node<V: 'static>(&mut self, node: impl Node<V, S> + 'static) -> Input<V> {
-        let value = Rc::clone(node.value_rc());
-        let erased = ErasedNode::new(node);
-        let idx = self.node_graph.borrow_mut().add_node(erased);
-        Input {
-            node_idx: idx,
-            value,
-        }
-    }
-
-    pub fn add_value<V: 'static>(&mut self, value: V) -> Input<V> {
-        return self.add_node(ConstNode::new(value));
-    }
-
-    pub fn add_rule<R>(&mut self, rule: R) -> Input<R::Output>
-    where
-        R: Rule,
-    {
-        return self.add_node(RuleNode::new(rule));
-    }
-
-    pub fn add_invalidatable_rule<R, F>(&mut self, mut f: F) -> Input<R::Output>
-    where
-        R: Rule,
-        F: FnMut(InvalidationSignal<S>) -> R,
-    {
-        let node_idx = Rc::new(Cell::new(None));
-        let signal = InvalidationSignal {
-            node_idx: Rc::clone(&node_idx),
-            graph: Rc::clone(&self.node_graph),
-        };
-        let input = self.add_rule(f(signal));
-        node_idx.set(Some(input.node_idx));
-        input
-    }
-
-    pub fn build(self) -> Result<Graph<O, S>, BuildGraphError> {
-        let output: &Input<O> = match &self.output {
-            None => return Err(BuildGraphError::NoOutput),
-            Some(output) => output,
-        };
-
-        let graph = self.node_graph.borrow();
-        let indices = graph.node_indices().collect::<Vec<_>>();
-        drop(graph);
-        let mut edges = vec![];
-        for idx in indices {
-            let node = &mut self.node_graph.borrow_mut()[idx];
-            node.visit_inputs(&mut |input_idx| {
-                edges.push((input_idx, idx));
-            });
-        }
-
-        for (source, dest) in edges {
-            self.node_graph.borrow_mut().add_edge(source, dest, ());
-        }
-
-        let mut graph = self.node_graph.borrow_mut();
-        util::remove_nodes_not_connected_to(&mut *graph, output.node_idx);
-        drop(graph);
-
-        let sorted = petgraph::algo::toposort(&**self.node_graph.borrow(), None);
-        if let Err(_cycle) = sorted {
-            self.node_graph.borrow_mut().clear_edges();
-            // TODO: actually build a vec describing the cycle path for debugging
-            return Err(BuildGraphError::Cyclic(vec![]));
-        }
-
-        let graph = Graph {
-            node_graph: self.node_graph,
-            output: self.output.unwrap(),
-            output_type: std::marker::PhantomData,
-        };
-
-        Ok(graph)
-    }
-}
-
-impl<O: 'static> GraphBuilder<O, Asynchronous> {
-    pub fn set_async_output<R: AsyncRule<Output = O>>(&mut self, rule: R) {
-        let input = self.add_async_rule(rule);
-        self.output = Some(input);
-    }
-
-    pub fn add_async_rule<R>(&mut self, rule: R) -> Input<R::Output>
-    where
-        R: AsyncRule,
-    {
-        self.add_node(AsyncRuleNode::new(rule))
-    }
-
-    pub fn add_invalidatable_async_rule<R, F>(&mut self, mut f: F) -> Input<R::Output>
-    where
-        R: AsyncRule,
-        F: FnMut(InvalidationSignal<Asynchronous>) -> R,
-    {
-        let node_idx = Rc::new(Cell::new(None));
-        let signal = InvalidationSignal {
-            node_idx: Rc::clone(&node_idx),
-            graph: Rc::clone(&self.node_graph),
-        };
-        let input = self.add_async_rule(f(signal));
-        node_idx.set(Some(input.node_idx));
-        input
-    }
-}
-
-#[derive(Debug)]
-pub enum BuildGraphError {
-    NoOutput,
-    Cyclic(Vec<NodeIndex<u32>>),
-}
-
 pub struct Graph<Output, Synch: Synchronicity> {
     node_graph: Rc<RefCell<NodeGraph<Synch>>>,
     output: Input<Output>,
@@ -287,7 +103,7 @@ impl<O: 'static, S: Synchronicity> Graph<O, S> {
 }
 
 impl<O: 'static> Graph<O, Synchronous> {
-    fn update_node(&mut self, idx: NodeIndex<u32>) {
+    fn update_node(&mut self, idx: NodeId) {
         let graph = self.node_graph.borrow();
         let node = &graph[idx];
         if !node.is_valid() {
@@ -307,7 +123,7 @@ impl<O: 'static> Graph<O, Synchronous> {
 
             let node = &mut self.node_graph.borrow_mut()[idx];
             // Actually update the node's value.
-            (node.update)(&mut node.any);
+            node.update();
         }
     }
 
@@ -318,7 +134,7 @@ impl<O: 'static> Graph<O, Synchronous> {
 }
 
 impl<O: 'static> Graph<O, Asynchronous> {
-    async fn update_node_async(&mut self, idx: NodeIndex<u32>) {
+    async fn update_node_async(&mut self, idx: NodeId) {
         // TODO: same note about recursing as above, and consider doing this in parallel
         let graph = self.node_graph.borrow();
         let node = &graph[idx];
@@ -335,7 +151,7 @@ impl<O: 'static> Graph<O, Asynchronous> {
 
             let mut graph = self.node_graph.borrow_mut();
             let node = &mut graph[idx];
-            (node.update)(&mut node.any).await;
+            node.update().await;
         }
     }
 
@@ -347,7 +163,7 @@ impl<O: 'static> Graph<O, Asynchronous> {
 
 #[derive(Debug)]
 pub struct Input<T> {
-    node_idx: NodeIndex<u32>,
+    node_idx: NodeId,
     value: Rc<RefCell<Option<T>>>,
 }
 
@@ -372,7 +188,7 @@ impl<T> Clone for Input<T> {
 
 // TODO: there's a lot happening here, make sure this doesn't create a reference cycle
 pub struct InvalidationSignal<Synch: Synchronicity> {
-    node_idx: Rc<Cell<Option<NodeIndex<u32>>>>,
+    node_idx: Rc<Cell<Option<NodeId>>>,
     graph: Rc<RefCell<NodeGraph<Synch>>>,
 }
 
@@ -384,10 +200,7 @@ impl<S: Synchronicity> InvalidationSignal<S> {
     }
 }
 
-fn invalidate_nodes<S: Synchronicity>(
-    graph: &mut NodeGraph<S>,
-    mut queue: VecDeque<NodeIndex<u32>>,
-) {
+fn invalidate_nodes<S: Synchronicity>(graph: &mut NodeGraph<S>, mut queue: VecDeque<NodeId>) {
     while let Some(idx) = queue.pop_front() {
         let node = &mut graph[idx];
         if node.is_valid() {
@@ -402,189 +215,6 @@ fn invalidate_nodes<S: Synchronicity>(
 
 // TODO: i really want Input to be able to implement Deref somehow
 
-pub struct ErasedNode<Synch: Synchronicity> {
-    any: Box<dyn Any>,
-    is_valid: Box<dyn Fn(&Box<dyn Any>) -> bool>,
-    invalidate: Box<dyn Fn(&mut Box<dyn Any>) -> ()>,
-    visit_inputs: Box<dyn Fn(&Box<dyn Any>, &mut dyn FnMut(NodeIndex<u32>) -> ()) -> ()>,
-    update: Synch::UpdateFn,
-}
-
-impl<S: Synchronicity> ErasedNode<S> {
-    fn new<N: Node<V, S> + 'static, V: 'static>(base: N) -> Self {
-        // i don't love the double boxing, but i'm not sure how else to do this
-        let thing: Box<dyn Node<V, S>> = Box::new(base);
-        let any: Box<dyn Any> = Box::new(thing);
-        Self {
-            any,
-            is_valid: Box::new(|any| {
-                let x = any.downcast_ref::<Box<dyn Node<V, S>>>().unwrap();
-                x.is_valid()
-            }),
-            invalidate: Box::new(|any| {
-                let x = any.downcast_mut::<Box<dyn Node<V, S>>>().unwrap();
-                x.invalidate();
-            }),
-            visit_inputs: Box::new(|any, visitor| {
-                let x = any.downcast_ref::<Box<dyn Node<V, S>>>().unwrap();
-                x.visit_inputs(visitor);
-            }),
-            update: S::make_update_fn::<V>(),
-        }
-    }
-
-    fn is_valid(&self) -> bool {
-        (self.is_valid)(&self.any)
-    }
-    fn invalidate(&mut self) {
-        (self.invalidate)(&mut self.any);
-    }
-    fn visit_inputs(&self, f: &mut dyn FnMut(NodeIndex<u32>) -> ()) {
-        (self.visit_inputs)(&self.any, f);
-    }
-}
-
-trait Node<Value: 'static, Synch: Synchronicity> {
-    fn is_valid(&self) -> bool;
-    fn invalidate(&mut self);
-    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeIndex<u32>) -> ());
-    fn update(&mut self) -> Synch::UpdateResult<'_>;
-    fn value_rc(&self) -> &Rc<RefCell<Option<Value>>>;
-}
-
-struct ConstNode<V, S> {
-    value: Rc<RefCell<Option<V>>>,
-    synchronicity: std::marker::PhantomData<S>,
-}
-
-impl<V, S> ConstNode<V, S> {
-    fn new(value: V) -> Self {
-        Self {
-            value: Rc::new(RefCell::new(Some(value))),
-            synchronicity: std::marker::PhantomData,
-        }
-    }
-}
-
-impl<V: 'static, S: Synchronicity> Node<V, S> for ConstNode<V, S> {
-    fn is_valid(&self) -> bool {
-        true
-    }
-
-    fn invalidate(&mut self) {}
-
-    fn visit_inputs(&self, _visitor: &mut dyn FnMut(NodeIndex<u32>) -> ()) {}
-
-    fn update(&mut self) -> S::UpdateResult<'_> {
-        unreachable!()
-    }
-
-    fn value_rc(&self) -> &Rc<RefCell<Option<V>>> {
-        &self.value
-    }
-}
-
-struct RuleNode<R, V, S> {
-    rule: R,
-    value: Rc<RefCell<Option<V>>>,
-    valid: bool,
-    synchronicity: std::marker::PhantomData<S>,
-}
-
-impl<R: Rule, S> RuleNode<R, R::Output, S> {
-    fn new(rule: R) -> Self {
-        Self {
-            rule,
-            value: Rc::new(RefCell::new(None)),
-            valid: false,
-            synchronicity: std::marker::PhantomData,
-        }
-    }
-}
-
-impl<R: Rule, S: Synchronicity> Node<R::Output, S> for RuleNode<R, R::Output, S> {
-    fn is_valid(&self) -> bool {
-        self.valid
-    }
-
-    fn invalidate(&mut self) {
-        self.valid = false;
-    }
-
-    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeIndex<u32>) -> ()) {
-        struct InputIndexVisitor<'a>(&'a mut dyn FnMut(NodeIndex<u32>) -> ());
-        impl<'a> InputVisitor for InputIndexVisitor<'a> {
-            fn visit<T>(&mut self, input: &Input<T>) {
-                self.0(input.node_idx);
-            }
-        }
-        self.rule.visit_inputs(&mut InputIndexVisitor(visitor));
-    }
-
-    fn update(&mut self) -> S::UpdateResult<'_> {
-        let new_value = self.rule.evaluate();
-        self.valid = true;
-        *self.value.borrow_mut() = Some(new_value);
-        S::make_update_result()
-    }
-
-    fn value_rc(&self) -> &Rc<RefCell<Option<R::Output>>> {
-        &self.value
-    }
-}
-
-struct AsyncRuleNode<R, V> {
-    rule: R,
-    value: Rc<RefCell<Option<V>>>,
-    valid: bool,
-}
-
-impl<R: AsyncRule> AsyncRuleNode<R, R::Output> {
-    fn new(rule: R) -> Self {
-        Self {
-            rule,
-            value: Rc::new(RefCell::new(None)),
-            valid: false,
-        }
-    }
-}
-
-impl<R: AsyncRule> Node<R::Output, Asynchronous> for AsyncRuleNode<R, R::Output> {
-    fn is_valid(&self) -> bool {
-        self.valid
-    }
-
-    fn invalidate(&mut self) {
-        self.valid = false;
-    }
-
-    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeIndex<u32>) -> ()) {
-        struct InputIndexVisitor<'a>(&'a mut dyn FnMut(NodeIndex<u32>) -> ());
-        impl<'a> InputVisitor for InputIndexVisitor<'a> {
-            fn visit<T>(&mut self, input: &Input<T>) {
-                self.0(input.node_idx);
-            }
-        }
-        self.rule.visit_inputs(&mut InputIndexVisitor(visitor));
-    }
-
-    fn update(&mut self) -> <Asynchronous as Synchronicity>::UpdateResult<'_> {
-        Box::pin(self.do_update())
-    }
-
-    fn value_rc(&self) -> &Rc<RefCell<Option<R::Output>>> {
-        &self.value
-    }
-}
-
-impl<R: AsyncRule> AsyncRuleNode<R, R::Output> {
-    async fn do_update(&mut self) {
-        let new_value = self.rule.evaluate().await;
-        self.valid = true;
-        *self.value.borrow_mut() = Some(new_value);
-    }
-}
-
 pub trait Rule: 'static {
     type Output;
 
diff --git a/crates/graph/src/node.rs b/crates/graph/src/node.rs
new file mode 100644
index 0000000..a4e3da5
--- /dev/null
+++ b/crates/graph/src/node.rs
@@ -0,0 +1,200 @@
+use crate::synchronicity::{Asynchronous, Synchronicity};
+use crate::{AsyncRule, Input, InputVisitor, NodeId, Rule, Synchronous};
+use std::any::Any;
+use std::cell::RefCell;
+use std::rc::Rc;
+
+pub(crate) struct ErasedNode<Synch: Synchronicity> {
+    any: Box<dyn Any>,
+    is_valid: Box<dyn Fn(&Box<dyn Any>) -> bool>,
+    invalidate: Box<dyn Fn(&mut Box<dyn Any>) -> ()>,
+    visit_inputs: Box<dyn Fn(&Box<dyn Any>, &mut dyn FnMut(NodeId) -> ()) -> ()>,
+    update: Synch::UpdateFn,
+}
+
+impl<S: Synchronicity> ErasedNode<S> {
+    pub(crate) fn new<N: Node<V, S> + 'static, V: 'static>(base: N) -> Self {
+        // i don't love the double boxing, but i'm not sure how else to do this
+        let thing: Box<dyn Node<V, S>> = Box::new(base);
+        let any: Box<dyn Any> = Box::new(thing);
+        Self {
+            any,
+            is_valid: Box::new(|any| {
+                let x = any.downcast_ref::<Box<dyn Node<V, S>>>().unwrap();
+                x.is_valid()
+            }),
+            invalidate: Box::new(|any| {
+                let x = any.downcast_mut::<Box<dyn Node<V, S>>>().unwrap();
+                x.invalidate();
+            }),
+            visit_inputs: Box::new(|any, visitor| {
+                let x = any.downcast_ref::<Box<dyn Node<V, S>>>().unwrap();
+                x.visit_inputs(visitor);
+            }),
+            update: S::make_update_fn::<V>(),
+        }
+    }
+
+    pub(crate) fn is_valid(&self) -> bool {
+        (self.is_valid)(&self.any)
+    }
+    pub(crate) fn invalidate(&mut self) {
+        (self.invalidate)(&mut self.any);
+    }
+    pub(crate) fn visit_inputs(&self, f: &mut dyn FnMut(NodeId) -> ()) {
+        (self.visit_inputs)(&self.any, f);
+    }
+}
+
+impl ErasedNode<Synchronous> {
+    pub(crate) fn update(&mut self) {
+        (self.update)(&mut self.any)
+    }
+}
+
+impl ErasedNode<Asynchronous> {
+    pub(crate) async fn update(&mut self) {
+        (self.update)(&mut self.any).await
+    }
+}
+
+pub(crate) trait Node<Value: 'static, Synch: Synchronicity> {
+    fn is_valid(&self) -> bool;
+    fn invalidate(&mut self);
+    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeId) -> ());
+    fn update(&mut self) -> Synch::UpdateResult<'_>;
+    fn value_rc(&self) -> &Rc<RefCell<Option<Value>>>;
+}
+
+pub(crate) struct ConstNode<V, S> {
+    value: Rc<RefCell<Option<V>>>,
+    synchronicity: std::marker::PhantomData<S>,
+}
+
+impl<V, S> ConstNode<V, S> {
+    pub(crate) fn new(value: V) -> Self {
+        Self {
+            value: Rc::new(RefCell::new(Some(value))),
+            synchronicity: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<V: 'static, S: Synchronicity> Node<V, S> for ConstNode<V, S> {
+    fn is_valid(&self) -> bool {
+        true
+    }
+
+    fn invalidate(&mut self) {}
+
+    fn visit_inputs(&self, _visitor: &mut dyn FnMut(NodeId) -> ()) {}
+
+    fn update(&mut self) -> S::UpdateResult<'_> {
+        unreachable!()
+    }
+
+    fn value_rc(&self) -> &Rc<RefCell<Option<V>>> {
+        &self.value
+    }
+}
+
+pub(crate) struct RuleNode<R, V, S> {
+    rule: R,
+    value: Rc<RefCell<Option<V>>>,
+    valid: bool,
+    synchronicity: std::marker::PhantomData<S>,
+}
+
+impl<R: Rule, S> RuleNode<R, R::Output, S> {
+    pub(crate) fn new(rule: R) -> Self {
+        Self {
+            rule,
+            value: Rc::new(RefCell::new(None)),
+            valid: false,
+            synchronicity: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<R: Rule, S: Synchronicity> Node<R::Output, S> for RuleNode<R, R::Output, S> {
+    fn is_valid(&self) -> bool {
+        self.valid
+    }
+
+    fn invalidate(&mut self) {
+        self.valid = false;
+    }
+
+    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeId) -> ()) {
+        struct InputIndexVisitor<'a>(&'a mut dyn FnMut(NodeId) -> ());
+        impl<'a> InputVisitor for InputIndexVisitor<'a> {
+            fn visit<T>(&mut self, input: &Input<T>) {
+                self.0(input.node_idx);
+            }
+        }
+        self.rule.visit_inputs(&mut InputIndexVisitor(visitor));
+    }
+
+    fn update(&mut self) -> S::UpdateResult<'_> {
+        let new_value = self.rule.evaluate();
+        self.valid = true;
+        *self.value.borrow_mut() = Some(new_value);
+        S::make_update_result()
+    }
+
+    fn value_rc(&self) -> &Rc<RefCell<Option<R::Output>>> {
+        &self.value
+    }
+}
+
+pub(crate) struct AsyncRuleNode<R, V> {
+    rule: R,
+    value: Rc<RefCell<Option<V>>>,
+    valid: bool,
+}
+
+impl<R: AsyncRule> AsyncRuleNode<R, R::Output> {
+    pub(crate) fn new(rule: R) -> Self {
+        Self {
+            rule,
+            value: Rc::new(RefCell::new(None)),
+            valid: false,
+        }
+    }
+}
+
+impl<R: AsyncRule> Node<R::Output, Asynchronous> for AsyncRuleNode<R, R::Output> {
+    fn is_valid(&self) -> bool {
+        self.valid
+    }
+
+    fn invalidate(&mut self) {
+        self.valid = false;
+    }
+
+    fn visit_inputs(&self, visitor: &mut dyn FnMut(NodeId) -> ()) {
+        struct InputIndexVisitor<'a>(&'a mut dyn FnMut(NodeId) -> ());
+        impl<'a> InputVisitor for InputIndexVisitor<'a> {
+            fn visit<T>(&mut self, input: &Input<T>) {
+                self.0(input.node_idx);
+            }
+        }
+        self.rule.visit_inputs(&mut InputIndexVisitor(visitor));
+    }
+
+    fn update(&mut self) -> <Asynchronous as Synchronicity>::UpdateResult<'_> {
+        Box::pin(self.do_update())
+    }
+
+    fn value_rc(&self) -> &Rc<RefCell<Option<R::Output>>> {
+        &self.value
+    }
+}
+
+impl<R: AsyncRule> AsyncRuleNode<R, R::Output> {
+    async fn do_update(&mut self) {
+        let new_value = self.rule.evaluate().await;
+        self.valid = true;
+        *self.value.borrow_mut() = Some(new_value);
+    }
+}
diff --git a/crates/graph/src/synchronicity.rs b/crates/graph/src/synchronicity.rs
new file mode 100644
index 0000000..f5e95e9
--- /dev/null
+++ b/crates/graph/src/synchronicity.rs
@@ -0,0 +1,53 @@
+use crate::node::Node;
+use std::any::Any;
+use std::future::Future;
+use std::pin::Pin;
+
+pub trait Synchronicity: 'static {
+    type UpdateFn;
+    fn make_update_fn<V: 'static>() -> Self::UpdateFn;
+
+    type UpdateResult<'a>;
+    fn make_update_result<'a>() -> Self::UpdateResult<'a>;
+}
+
+pub struct Synchronous;
+
+impl Synchronicity for Synchronous {
+    type UpdateFn = Box<dyn Fn(&mut Box<dyn Any>) -> ()>;
+
+    fn make_update_fn<V: 'static>() -> Self::UpdateFn {
+        Box::new(|any| {
+            let x = any.downcast_mut::<Box<dyn Node<V, Self>>>().unwrap();
+            x.update();
+        })
+    }
+
+    type UpdateResult<'a> = ();
+
+    fn make_update_result<'a>() -> Self::UpdateResult<'a> {}
+}
+
+pub struct Asynchronous;
+
+impl Synchronicity for Asynchronous {
+    type UpdateFn =
+        Box<dyn for<'a> Fn(&'a mut Box<dyn Any>) -> Pin<Box<dyn Future<Output = ()> + 'a>>>;
+
+    fn make_update_fn<V: 'static>() -> Self::UpdateFn {
+        Box::new(|any| Box::pin(Asynchronous::do_async_update::<V>(any)))
+    }
+
+    type UpdateResult<'a> = Pin<Box<dyn Future<Output = ()> + 'a>>;
+
+    fn make_update_result<'a>() -> Self::UpdateResult<'a> {
+        Box::pin(std::future::ready(()))
+    }
+}
+
+impl Asynchronous {
+    async fn do_async_update<V: 'static>(any: &mut Box<dyn Any>) {
+        let x = any.downcast_mut::<Box<dyn Node<V, Self>>>().unwrap();
+        x.update().await;
+    }
+}