diff --git a/lib/cast.hpp b/lib/cast.hpp
new file mode 100644
index 0000000..d0d8d4f
--- /dev/null
+++ b/lib/cast.hpp
@@ -0,0 +1,26 @@
+#include "commons.hpp"
+
+extern "C" void lib_cast(grino::Loader& loader)
+{
+  grino::Loc loc {"core/casts"};
+
+  loader.add_native("stoi", [loc](auto args){
+    std::string value = args[0]->as_string();
+    return grino::Value::make_int(loc, std::stoi(value));
+  });
+
+  loader.add_native("itos", [loc](auto args){
+    int value = args[0]->as_int();
+    return grino::Value::make_string(loc, std::to_string(value));
+  });
+
+  loader.add_native("stof", [loc](auto args){
+    std::string value = args[0]->as_string();
+    return grino::Value::make_int(loc, std::stof(value));
+  });
+
+  loader.add_native("ftos", [loc](auto args){
+    float value = args[0]->as_float();
+    return grino::Value::make_string(loc, std::to_string(value));
+  });
+}
diff --git a/lib/commons.hpp b/lib/commons.hpp
new file mode 100644
index 0000000..5d91bc0
--- /dev/null
+++ b/lib/commons.hpp
@@ -0,0 +1,5 @@
+#include "../src/Loader.hpp"
+#include "src/Logger.hpp"
+#include "src/Value.hpp"
+#include "src/opcodes.hpp"
+#include "../src/Module.hpp"
diff --git a/lib/core.cpp b/lib/core.cpp
index 4527ab4..6076f2f 100644
--- a/lib/core.cpp
+++ b/lib/core.cpp
@@ -3,6 +3,7 @@
 #include "src/Value.hpp"
 #include "src/opcodes.hpp"
 #include "../src/Module.hpp"
+#include "cast.hpp"
 
 GRINO_ERROR(assertion_error);
 
@@ -671,6 +672,7 @@ extern "C" void lib(grino::Loader& loader)
   lib_collection(loader);
   lib_array(loader);
   lib_string(loader);
+  lib_cast(loader);
 
   loader.add_native("dump", [](auto args){
     std::string sep;
diff --git a/lib/std/io.hpp b/lib/std/io.hpp
index 1bd258c..b5a6076 100644
--- a/lib/std/io.hpp
+++ b/lib/std/io.hpp
@@ -21,4 +21,11 @@ extern "C" void lib_io(grino::Loader& loader)
     std::cout << std::endl;
     return grino::Value::make_nil(grino::Loc {"io"});
   });
+
+  mod->loader()->add_native("read", [](auto args){
+    std::string value;
+    std::cin >> value;
+
+    return grino::Value::make_string(grino::Loc {"io"}, value);
+  });
 }
diff --git a/lib/std/rand.hpp b/lib/std/rand.hpp
new file mode 100644
index 0000000..7cfb7ac
--- /dev/null
+++ b/lib/std/rand.hpp
@@ -0,0 +1,33 @@
+#include <random>
+#include <chrono>
+
+#include "src/Loader.hpp"
+#include "src/Module.hpp"
+
+extern "C" void lib_rand(grino::Loader& loader)
+{
+  grino::Loc loc {"core/rand"};
+  auto mod = loader.add_module("rand");
+
+  mod->loader()->add_native("randf", [loc](auto args){
+    std::mt19937 r;
+
+    r.seed(std::chrono::steady_clock::now().time_since_epoch().count());
+
+    std::uniform_real_distribution<float> urd(0.0f, 1.0f);
+
+    return grino::Value::make_float(loc, urd(r));
+  });
+
+  mod->loader()->add_native("range", [loc](auto args){
+    std::mt19937 r;
+
+    r.seed(std::chrono::steady_clock::now().time_since_epoch().count());
+    int from = args[0]->as_int();
+    int to = args[1]->as_int();
+
+    std::uniform_int_distribution<int> dist(from, to);
+
+    return grino::Value::make_int(loc, dist(r));
+  });
+}
diff --git a/lib/std/std.cpp b/lib/std/std.cpp
index 079738f..3c171b3 100644
--- a/lib/std/std.cpp
+++ b/lib/std/std.cpp
@@ -1,8 +1,10 @@
 #include "src/Loader.hpp"
 
 #include "io.hpp"
+#include "rand.hpp"
 
 extern "C" void lib(grino::Loader& loader)
 {
   lib_io(loader);
+  lib_rand(loader);
 }
diff --git a/src/VM.cpp b/src/VM.cpp
index e56f69c..7060075 100644
--- a/src/VM.cpp
+++ b/src/VM.cpp
@@ -212,7 +212,6 @@ namespace grino
                           {
                             if (fun)
                               {
-                                std::cout << "store INIT" << std::endl;
                                 fun->set_env(itr->first,
                                              Value::make_copy(itr->second->loc(),
                                                               itr->second));