diff --git a/lib/core.cpp b/lib/core.cpp
index 930b47e..632ba61 100644
--- a/lib/core.cpp
+++ b/lib/core.cpp
@@ -3,8 +3,54 @@
 
 GRINO_ERROR(assertion_error);
 
+extern "C" void lib_assert(grino::Loader& loader)
+{
+    loader.add_native("assert", [](auto args){
+
+    for (auto value: args)
+      {
+        if (!value->as_bool())
+          {
+            grino::Logger logger;
+            logger.log<assertion_error>(grino::LOG_ASSERT,
+                                        value->loc(),
+                                        "assertion failed");
+          }
+      }
+
+    return grino::Value::make_bool(args.front()->loc(), true);
+  });
+
+      loader.add_native("assert-eq?", [](auto args){
+    auto lhs = args.front();
+
+    for (size_t i=1; i<args.size(); i++)
+      {
+        auto rhs = args[i];
+
+        if (!lhs->equals(*rhs))
+          {
+            grino::Logger logger;
+            std::stringstream ss;
+
+            ss << "'" << lhs->string() << "' is not equals to '"
+               << rhs->string() << "'";
+
+            logger.log<assertion_error>(grino::LOG_ASSERT,
+                                        lhs->loc(),
+                                        ss.str());
+
+          }
+      }
+
+    return grino::Value::make_bool(args.front()->loc(), true);
+  });
+}
+
 extern "C" void lib(grino::Loader& loader)
 {
+  lib_assert(loader);
+
   loader.add_native("dump", [](auto args){
     std::string sep;
     std::stringstream ss;
@@ -20,16 +66,16 @@ extern "C" void lib(grino::Loader& loader)
     return grino::Value::make_nil(args.back()->loc());
   });
 
-  loader.add_native("assert", [](auto args){
+  loader.add_native("eq?", [](auto args){
+    auto lhs = args.front();
 
-    for (auto value: args)
+    for (size_t i=1; i<args.size(); i++)
       {
-        if (!value->as_bool())
+        auto rhs = args[i];
+
+        if (!lhs->equals(*rhs))
           {
-            grino::Logger logger;
-            logger.log<assertion_error>(grino::LOG_ASSERT,
-                                        value->loc(),
-                                        "assertion failed");
+            return grino::Value::make_bool(rhs->loc(), false);
           }
       }