diff --git a/Cargo.lock b/Cargo.lock
index 9574549..8d47dc8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -76,7 +76,7 @@ checksum = "b4682ae6287fcf752ecaabbfcc7b6f9b72aa33933dc23a554d853aea8eea8635"
 
 [[package]]
 name = "calcit"
-version = "0.9.3"
+version = "0.9.4"
 dependencies = [
  "argh",
  "cirru_edn",
diff --git a/Cargo.toml b/Cargo.toml
index f4cc615..932a2dc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "calcit"
-version = "0.9.3"
+version = "0.9.4"
 authors = ["jiyinyiyong <jiyinyiyong@gmail.com>"]
 edition = "2021"
 license = "MIT"
diff --git a/package.json b/package.json
index 93f45c6..3951f5a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@calcit/procs",
-  "version": "0.9.3",
+  "version": "0.9.4",
   "main": "./lib/calcit.procs.mjs",
   "devDependencies": {
     "@types/node": "^22.1.0",
diff --git a/ts-src/js-list.mts b/ts-src/js-list.mts
index bbec863..a0ebbd3 100644
--- a/ts-src/js-list.mts
+++ b/ts-src/js-list.mts
@@ -123,6 +123,8 @@ export class CalcitSliceList {
   start: number;
   end: number;
   cachedHash: Hash;
+  /** reference to converted list */
+  cachedTreeListRef: CalcitList;
   constructor(value: Array<CalcitValue>) {
     if (value == null) {
       value = []; // dirty, better handled from outside
@@ -134,7 +136,12 @@ export class CalcitSliceList {
     this.end = value.length;
   }
   turnListMode(): CalcitList {
-    return new CalcitList(initTernaryTreeListFromRange(this.value, this.start, this.end));
+    if (this.cachedTreeListRef != null) {
+      return this.cachedTreeListRef;
+    }
+    let ret = new CalcitList(initTernaryTreeListFromRange(this.value, this.start, this.end));
+    this.cachedTreeListRef = ret;
+    return ret;
   }
   len() {
     return this.end - this.start;
diff --git a/ts-src/js-map.mts b/ts-src/js-map.mts
index 7e3fc28..b656f56 100644
--- a/ts-src/js-map.mts
+++ b/ts-src/js-map.mts
@@ -194,6 +194,8 @@ export class CalcitSliceMap {
   cachedHash: Hash;
   /** in arrayMode, only flatten values, instead of tree structure */
   chunk: CalcitValue[];
+  /** reference to generated HashMap in tree structure */
+  cachedTreeMapRef?: CalcitMap;
   constructor(value: CalcitValue[]) {
     if (value == null) {
       this.chunk = [];
@@ -203,14 +205,20 @@ export class CalcitSliceMap {
       throw new Error("unknown data for map");
     }
   }
+  /** convert to tree map when needed, also cached in case converted over and over again  */
   turnMap(): CalcitMap {
+    if (this.cachedTreeMapRef != null) {
+      return this.cachedTreeMapRef;
+    }
     var dict: Array<[CalcitValue, CalcitValue]> = [];
     let halfLength = this.chunk.length >> 1;
     for (let idx = 0; idx < halfLength; idx++) {
       dict.push([this.chunk[idx << 1], this.chunk[(idx << 1) + 1]]);
     }
     let value = initTernaryTreeMapFromArray(dict);
-    return new CalcitMap(value);
+    let ret = new CalcitMap(value);
+    this.cachedTreeMapRef = ret;
+    return ret;
   }
   len() {
     return this.chunk.length >> 1;