diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
index 5f2fdce0..49571ff9 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
@@ -24,22 +24,35 @@ module Private = {
 
   let createProject = () => {
     let project: t = {
-      "tag": "reducerProject",
+      "iAmProject": true,
       "items": Belt.Map.String.empty,
       "stdLib": ReducerInterface_StdLib.internalStdLib,
       "environment": InternalExpressionValue.defaultEnvironment,
+      "previousRunOrder": [],
     }
     project
   }
 
-  let rec touchSource = (project: t, sourceId: string): unit => {
+  let rec touchSource_ = (project: t, sourceId: string): unit => {
     let item = project->getItem(sourceId)
     let newItem = ProjectItem.touchSource(item)
     Belt.Map.String.set(project["items"], sourceId, newItem)->T.Private.setFieldItems(project, _)
-    touchDependents(project, sourceId)
   }
   and touchDependents = (project: t, sourceId: string): unit => {
-    let _ = getDependents(project, sourceId)->Belt.Array.forEach(_, touchSource(project, _))
+    let _ = getDependents(project, sourceId)->Belt.Array.forEach(_, touchSource_(project, _))
+  }
+
+  let touchSource = (project: t, sourceId: string): unit => {
+    touchSource_(project, sourceId)
+    touchDependents(project, sourceId)
+  }
+
+  let handleNewTopology = (project: t): unit => {
+    let previousRunOrder = project["previousRunOrder"]
+    let currentRunOrder = Topology.getRunOrder(project)
+    let diff = Topology.runOrderDiff(currentRunOrder, previousRunOrder)
+    Belt.Array.forEach(diff, touchSource(project, _))
+    T.Private.setFieldPreviousRunOrder(project, currentRunOrder)
   }
 
   let getSource = (project: t, sourceId: string): option<string> =>
@@ -73,7 +86,7 @@ module Private = {
   let setContinues = (project: t, sourceId: string, continues: array<string>): unit => {
     let newItem = project->getItem(sourceId)->ProjectItem.setContinues(continues)
     Belt.Map.String.set(project["items"], sourceId, newItem)->T.Private.setFieldItems(project, _)
-    touchSource(project, sourceId)
+    handleNewTopology(project)
   }
   let getContinues = (project: t, sourceId: string): array<string> =>
     ProjectItem.getContinues(project->getItem(sourceId))
@@ -81,7 +94,7 @@ module Private = {
   let removeContinues = (project: t, sourceId: string): unit => {
     let newItem = project->getItem(sourceId)->ProjectItem.removeContinues
     Belt.Map.String.set(project["items"], sourceId, newItem)->T.Private.setFieldItems(project, _)
-    touchSource(project, sourceId)
+    handleNewTopology(project)
   }
 
   let getContinuation = (project: t, sourceId: string): ProjectItem.T.continuationArgumentType =>
@@ -113,6 +126,7 @@ module Private = {
   let parseIncludes = (project: t, sourceId: string): unit => {
     let newItem = project->getItem(sourceId)->ProjectItem.parseIncludes
     Belt.Map.String.set(project["items"], sourceId, newItem)->T.Private.setFieldItems(project, _)
+    handleNewTopology(project)
   }
 
   let rawParse = (project: t, sourceId): unit => {
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_T.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_T.res
index a9411c43..e1ec91f4 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_T.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_T.res
@@ -3,17 +3,18 @@ module ExpressionT = Reducer_Expression_T
 module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
 
 @genType.opaque
-type project = {"tag": string}
+type project = {"iAmProject": bool}
 //re-export
 @genType
 type t = project
 
 module Private = {
   type internalProject = {
-    "tag": string,
+    "iAmProject": bool,
     "items": Belt.Map.String.t<ProjectItem.t>,
     "stdLib": Reducer_Bindings.t,
     "environment": ExpressionT.environment,
+    "previousRunOrder": array<string>,
   }
   type t = internalProject
 
@@ -22,7 +23,9 @@ module Private = {
   @set
   external setFieldStdLib: (t, Reducer_Bindings.t) => unit = "stdLib"
   @set
-  external setFieldEnvironment: (t, ExpressionT.environment) => unit = "stdLib"
+  external setFieldEnvironment: (t, ExpressionT.environment) => unit = "environment"
+  @set
+  external setFieldPreviousRunOrder: (t, array<string>) => unit = "previousRunOrder"
 
   external castFromInternalProject: t => project = "%identity"
   external castToInternalProject: project => t = "%identity"