added "dynamic" fields (get/set/call fields by name using dynamic standard function

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Script.kt

@@ -170,6 +170,11 @@ class Script(
                 }
                 result ?: raiseError(ObjAssertionFailedException(this,"Expected exception but nothing was thrown"))
             }
+
+            addFn("dynamic") {
+                ObjDynamic.create(this, requireOnlyArg())
+            }
+
             addFn("require") {
                 val condition = requiredArg<ObjBool>(0)
                 if( !condition.value ) {

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjDynamic.kt

@@ -0,0 +1,65 @@
+package net.sergeych.lyng.obj
+
+import net.sergeych.lyng.Arguments
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.Statement
+
+class ObjDynamicContext(val delegate: ObjDynamic) : Obj() {
+    override val objClass: ObjClass = type
+
+    companion object {
+        val type = ObjClass("DelegateContext").apply {
+            addFn("get") {
+                val d = thisAs<ObjDynamicContext>().delegate
+                if (d.readCallback != null)
+                    raiseIllegalState("get already defined")
+                d.readCallback = requireOnlyArg()
+                ObjVoid
+            }
+
+            addFn("set") {
+                val d = thisAs<ObjDynamicContext>().delegate
+                if (d.writeCallback != null)
+                    raiseIllegalState("set already defined")
+                d.writeCallback = requireOnlyArg()
+                ObjVoid
+            }
+
+        }
+
+    }
+}
+
+class ObjDynamic : Obj() {
+
+    internal var readCallback: Statement? = null
+    internal var writeCallback: Statement? = null
+
+    override suspend fun readField(scope: Scope, name: String): ObjRecord {
+        return readCallback?.execute(scope.copy(Arguments(ObjString(name))))?.let {
+            if (writeCallback != null)
+                it.asMutable
+            else
+                it.asReadonly
+        }
+            ?: super.readField(scope, name)
+    }
+
+    override suspend fun writeField(scope: Scope, name: String, newValue: Obj) {
+        writeCallback?.execute(scope.copy(Arguments(ObjString(name), newValue)))
+            ?: super.writeField(scope, name, newValue)
+    }
+
+    companion object {
+
+        suspend fun create(scope: Scope, builder: Statement): ObjDynamic {
+            val delegate = ObjDynamic()
+            val context = ObjDynamicContext(delegate)
+            builder.execute(scope.copy(newThisObj = context))
+            return delegate
+        }
+
+        val type = object : ObjClass("Delegate") {}
+    }
+
+}