diff --git a/docs/samples/happy_numbers.lyng.bad b/docs/samples/happy_numbers.lyng.bad
index e66d13f..ec71429 100644
--- a/docs/samples/happy_numbers.lyng.bad
+++ b/docs/samples/happy_numbers.lyng.bad
@@ -19,12 +19,13 @@ fun naiveCountHappyNumbers() {
 import lyng.time
 
 //
-// After all optimizations it takes ~120ms.
+// After all optimizations it took ~120ms - before.
 //
-for( r in 1..100 ) {
+for( r in 1..900 ) {
     val start = Instant.now()
     val found = naiveCountHappyNumbers()
     println("Found happy numbers: %d time %s"(found, Instant.now() - start))
     assert( found == 55252 )
-    delay(0.1)
-}
\ No newline at end of file
+    delay(0.05)
+}
+
diff --git a/lynglib/build.gradle.kts b/lynglib/build.gradle.kts
index 622a1f9..d4abb71 100644
--- a/lynglib/build.gradle.kts
+++ b/lynglib/build.gradle.kts
@@ -21,7 +21,7 @@ import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 group = "net.sergeych"
-version = "0.10.1-SNAPSHOT"
+version = "0.10.2-SNAPSHOT"
 
 buildscript {
     repositories {
diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt
index dffb0d7..c0bb6dc 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt
@@ -124,7 +124,7 @@ open class Obj {
      * @param calledFromLyng true if called from Lyng's `toString`. Normally this parameter should be ignored,
      *      but it is used to avoid endless recursion in [Obj.toString] base implementation
      */
-    suspend open fun toString(scope: Scope,calledFromLyng: Boolean=false): ObjString {
+    open suspend fun toString(scope: Scope,calledFromLyng: Boolean=false): ObjString {
         return if (this is ObjString) this
         else if( !calledFromLyng ) {
             invokeInstanceMethod(scope, "toString") {
@@ -265,7 +265,7 @@ open class Obj {
     }
 
     suspend fun invoke(scope: Scope, thisObj: Obj, args: Arguments): Obj =
-        if (net.sergeych.lyng.PerfFlags.SCOPE_POOL)
+        if (PerfFlags.SCOPE_POOL)
             scope.withChildFrame(args, newThisObj = thisObj) { child ->
                 callOn(child)
             }
@@ -300,7 +300,7 @@ open class Obj {
     open suspend fun lynonType(): LynonType = LynonType.Other
 
     open suspend fun serialize(scope: Scope, encoder: LynonEncoder, lynonType: LynonType?) {
-        scope.raiseNotImplemented()
+        scope.raiseNotImplemented("lynon: can't serialize ${this.objClass}:${this.toString(scope)}")
     }
 
     fun autoInstanceScope(parent: Scope): Scope {