diff --git a/src/main/scala/esmeta/peval/pstate/Reachable.scala b/src/main/scala/esmeta/peval/pstate/Reachable.scala
new file mode 100644
index 0000000000..9444cb3e5b
--- /dev/null
+++ b/src/main/scala/esmeta/peval/pstate/Reachable.scala
@@ -0,0 +1,39 @@
+package esmeta.peval.pstate
+
+import esmeta.state.*
+import esmeta.state.util.{UnitWalker}
+import scala.collection.mutable.{Set as MSet}
+import esmeta.ir.Var
+
+class Reachable private () extends UnitWalker {
+  
+  val addrs = MSet.empty[Addr]
+
+  override def walk(id: Var): Unit = 
+
+  override def walk(v: Value): Unit = v match
+    case addr: Addr => 
+    case Clo(func, captured) =>
+    case PClo(func, captured) =>
+    case Cont(func, captured, callStack) =>
+    case PCont(func, captured, callStack) =>
+    case AstValue(ast) =>
+    case GrammarSymbol(name, params) =>
+    case esmeta.state.Math(decimal) =>
+    case Infinity(pos) =>
+    case esmeta.state.Enum(name) =>
+    case CodeUnit(c) =>
+    case esmeta.state.Number(double) =>
+    case esmeta.state.BigInt(bigInt) =>
+    case Str(str) =>
+    case Bool(bool) =>
+    case Undef =>
+    case esmeta.state.Null =>
+  
+}
+
+object Reachable {
+
+  def from(addr: Predict[Value])(using pst : PState): Set[Addr] =
+
+}
\ No newline at end of file
diff --git a/src/main/scala/esmeta/peval/pstate/UnitWalker.scala b/src/main/scala/esmeta/peval/pstate/UnitWalker.scala
new file mode 100644
index 0000000000..7c1715bc2f
--- /dev/null
+++ b/src/main/scala/esmeta/peval/pstate/UnitWalker.scala
@@ -0,0 +1,117 @@
+package esmeta.peval.pstate
+
+import esmeta.state.*
+import esmeta.state.util.{UnitWalker as StateUnitWalker}
+import esmeta.ir.*
+import esmeta.util.BasicUnitWalker
+
+import esmeta.peval.{Predict, Known, Unknown}
+import scala.annotation.targetName
+
+/** unit walker for state */
+trait UnitWalker extends StateUnitWalker {
+
+  def walk(pst: PState): Unit =
+    val PState(globals, callStack, context, heap) = pst
+    walkMap(globals, walk, walk);
+    walkList(callStack)
+    walk(callStack);
+    walk(context);
+    walk(heap);
+
+  def walk(pcc: PCallContext): Unit =
+    val PCallContext(ctxt, redId) = pcc
+    walk(ctxt)
+    walk(redId)
+
+  def walk(pctx: PContext): Unit =
+    val PContext(func, sensitivity, locals, ret) = pctx
+    walK(func)
+    walk(sensitivity)
+    walk(locals)
+    walk(ret)
+
+  @targetName("walkPV")
+  def walk(pv: Predict[Value]): Unit = pv match
+    case Known(v) => walk(v)
+    case Unknown  =>
+
+  @targetName("walkPRT")
+  def walk(pr: Predict[RefTarget]): Unit = pr match
+    case Known(tgt) => walk(tgt)
+    case Unknown    =>
+
+  // all cases
+  def walk(elem: StateElem): Unit = elem match
+    case elem: State       => walk(elem)
+    case elem: Context     => walk(elem)
+    case elem: Cursor      => walk(elem)
+    case elem: CallContext => walk(elem)
+    case elem: Heap        => walk(elem)
+    case elem: Obj         => walk(elem)
+    case elem: Value       => walk(elem)
+    case elem: RefTarget   => walk(elem)
+    case elem: Uninit      => walk(elem)
+
+  // states
+  def walk(st: State): Unit =
+    val State(_, context, _, _, _, callStack, globals, heap) = st
+    walk(context)
+    walkList(callStack, walk)
+    walkMMap(globals, walk, walk)
+    walk(heap)
+
+  // context
+  def walk(context: Context): Unit =
+    walkMMap(context.locals, walk, walk)
+    context.retVal.map { case (_, value) => walk(value) }
+
+  // cursor
+  def walk(cursor: Cursor): Unit = {}
+
+  // calling contexts
+  def walk(callContext: CallContext): Unit = walk(callContext.context)
+
+  // heap
+  def walk(heap: Heap): Unit = walkMMap(heap.map, walk, walk)
+
+  // object
+  def walk(obj: Obj): Unit = obj match
+    case RecordObj(_, map) => walkMMap(map, walk, walk)
+    case MapObj(map)       => walkMMap(map, walk, walk)
+    case ListObj(values)   => walkIterable(values, walk)
+    case _: YetObj         =>
+
+  // value
+  def walk(v: Value): Unit = v match
+    case addr: Addr       => walk(addr)
+    case Clo(_, captured) => walkMap(captured, walk, walk)
+    case Cont(_, captured, callStack) =>
+      walkMap(captured, walk, walk); walkList(callStack, walk)
+    case _: AstValue                   =>
+    case _: GrammarSymbol              =>
+    case _: Math                       =>
+    case _: Infinity                   =>
+    case _: Enum                       =>
+    case _: CodeUnit                   =>
+    case sv: SimpleValue               => walk(sv)
+    case PClo(_, captrued)             => ???
+    case PCont(_, captured, callStack) => ???
+
+  // address
+  def walk(addr: Addr): Unit = {}
+
+  // simple value
+  def walk(sv: SimpleValue): Unit = {}
+
+  // reference value
+  def walk(rv: RefTarget): Unit = rv match
+    case _: VarTarget             =>
+    case FieldTarget(base, field) => walk(base); walk(field)
+
+  // ir id
+  def walk(id: Var): Unit = {}
+
+  // uninit value
+  def walk(uninit: Uninit): Unit = {}
+}