diff --git a/implementations/javascript/packages/core/src/pexpr.ts b/implementations/javascript/packages/core/src/pexpr.ts
index c3a6aff..e5be35e 100644
--- a/implementations/javascript/packages/core/src/pexpr.ts
+++ b/implementations/javascript/packages/core/src/pexpr.ts
@@ -282,7 +282,7 @@ export class Reader extends ReaderBase<never> {
 
 export interface AsPreservesOptions<T extends Embeddable> {
     onGroup?: (g: Positioned<Group>) => Value<T>;
-    onEmbedded?: (v: Value<T>) => Value<T>;
+    onEmbedded?: (e: Positioned<Expr>, walk: (p: Positioned<Expr>) => Value<T>) => Value<T>;
     error?: (tag: string, position: Position) => Value<T>;
 }
 
@@ -302,9 +302,8 @@ export function asPreserves<T extends Embeddable>(
         if (p.item instanceof Punct) {
             return error('invalid-punctuation', p.position);
         } else if (p.item instanceof Embedded) {
-            const e = walk({ position: p.position, item: p.item.expr });
             if (options.onEmbedded) {
-                return options.onEmbedded(e);
+                return options.onEmbedded({ position: p.position, item: p.item.expr }, walk);
             } else {
                 return error('unexpected-embedded', p.position);
             }