diff --git a/src/common.cpp b/src/common.cpp
index 7aefbf0..e6ec737 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -328,7 +328,7 @@ Result<Value> StackFrame::get(uint64_t idx) const {
   return Value::create(_value->data[idx].get());
 }
 
-Result<StackFrame> StackFrame::set(uint64_t idx, const Value& val) {
+Result<StackFrame> StackFrame::set(uint64_t idx, const Value& val) const {
   uint64_t size = std::max(_value->size, idx + 1);
   auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
   pod->header.tag = Tag::StackFrame;
diff --git a/src/common.hpp b/src/common.hpp
index 7448353..0bc4914 100644
--- a/src/common.hpp
+++ b/src/common.hpp
@@ -1114,7 +1114,7 @@ class StackFrame : public Object {
 
   using Object::get;
   Result<Value> get(uint64_t idx) const;
-  Result<StackFrame> set(uint64_t idx, const Value& val);
+  Result<StackFrame> set(uint64_t idx, const Value& val) const;
   Result<StackFrame> settop(uint64_t idx) const;
   Result<Value> parent() const;
   Result<Value> fun() const;
diff --git a/src/stdlib.cpp b/src/stdlib.cpp
index 43ac346..8d882d2 100644
--- a/src/stdlib.cpp
+++ b/src/stdlib.cpp
@@ -5,7 +5,7 @@
 #include "sourcerange.hpp"
 #include "writer.hpp"
 
-typedef Result<Value> (*StdlibFunctionIdPtr)(const Array& params);
+typedef Result<StackFrame> (*StdlibFunctionIdPtr)(const StackFrame& stack);
 
 struct StdlibFunctionEntry {
   const char* name;
@@ -13,11 +13,12 @@ struct StdlibFunctionEntry {
   StdlibFunctionIdPtr fun_ptr;
 };
 
-Result<Value> stdlib_unknown(const Array& params) {
+Result<StackFrame> stdlib_unknown(const StackFrame& stack) {
   return ERROR(NotImplemented);
 }
 
-Result<Value> stdlib_print(const Array& params) {
+Result<StackFrame> stdlib_print(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
   auto size = TRY(params.size());
   for (uint64_t i = 0; i < size; i++) {
     Value param = TRY(params.get(i));
@@ -33,19 +34,25 @@ Result<Value> stdlib_print(const Array& params) {
     }
   }
 
-  return Value(TRY(Nil::create()));
+  auto nil = Value(TRY(Nil::create()));
+  auto res = TRY(stack.set(0, nil));
+
+  return res.ret(0);
 }
 
-Result<Value> stdlib_println(const Array& params) {
-  TRY(stdlib_print(params));
+Result<StackFrame> stdlib_println(const StackFrame& stack) {
+  auto res = TRY(stdlib_print(stack));
   std::cout << "\n";
 
-  return Value(TRY(Nil::create()));
+  return res;
 }
 
-Result<Value> stdlib_prn(const Array& params) { return ERROR(NotImplemented); }
+Result<StackFrame> stdlib_prn(const StackFrame& stack) {
+  return ERROR(NotImplemented);
+}
 
-Result<Value> stdlib_assert(const Array& params) {
+Result<StackFrame> stdlib_assert(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
   auto size = TRY(params.size());
   for (uint64_t i = 0; i < size; i++) {
     Value param = TRY(params.get(i));
@@ -54,40 +61,59 @@ Result<Value> stdlib_assert(const Array& params) {
     if (!v) return ERROR(AssertionFailed);
   }
 
-  return Value(TRY(Nil::create()));
+  auto nil = Value(TRY(Nil::create()));
+  auto res = TRY(stack.set(0, nil));
+
+  return res.ret(0);
 }
 
-Result<Value> stdlib_dict(const Array& params) {
-  Value d = TRY(Dict::create(params));
-  return d;
+Result<StackFrame> stdlib_dict(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
+  if (!params.is<Array>()) return ERROR(TypeMismatch);
+  Value d = TRY(Dict::create(*params.to<Array>()));
+
+  auto res = TRY(stack.set(0, d));
+  return res.ret(0);
 }
 
-Result<Value> stdlib_list(const Array& params) {
-  Value d = TRY(Pair::create(params));
-  return d;
+Result<StackFrame> stdlib_list(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
+  if (!params.is<Array>()) return ERROR(TypeMismatch);
+  Value d = TRY(Pair::create(*params.to<Array>()));
+
+  auto res = TRY(stack.set(0, d));
+  return res.ret(0);
 }
 
-Result<Value> stdlib_array(const Array& params) {
-  Array array_copy = TRY(params.copy());
-  return Value(std::move(array_copy));
+Result<StackFrame> stdlib_array(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
+
+  auto res = TRY(stack.set(0, params));
+  return res.ret(0);
 }
 
-Result<Value> stdlib_get(const Array& params) {
+Result<StackFrame> stdlib_get(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
   auto size = TRY(params.size());
   if (size != 2) return ERROR(ArgumentCountMismatch);
+
   Value collection = TRY(params.get(0));
   Value key = TRY(params.get(1));
-  return TRY(collection.get(key));
+
+  auto val = TRY(collection.get(key));
+
+  auto res = TRY(stack.set(0, val));
+  return res.ret(0);
 }
 
-Result<Value> stdlib_srcloc(const Array& params) {
-  Array array_copy = TRY(params.copy());
+Result<StackFrame> stdlib_srcloc(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
   auto size = TRY(params.size());
   if (size != 6) return ERROR(ArgumentCountMismatch);
 
   SourceRange sr;
   for (uint64_t i = 0; i < 6; i++) {
-    auto val = TRY(array_copy.get(i));
+    auto val = TRY(params.get(i));
     if (!val.is<Int64>()) return ERROR(TypeMismatch);
     int64_t intval = val.to<Int64>()->value();
     switch (i) {
@@ -114,16 +140,25 @@ Result<Value> stdlib_srcloc(const Array& params) {
     }
   }
 
-  return Value(TRY(SrcLoc::create(sr)));
+  auto val = Value(TRY(SrcLoc::create(sr)));
+
+  auto res = TRY(stack.set(0, val));
+  return res.ret(0);
 }
 
-Result<Value> stdlib_size(const Array& params) {
+Result<StackFrame> stdlib_size(const StackFrame& stack) {
+  auto params = TRY(stack.get(0));
   auto size = TRY(params.size());
+
   if (size != 1) return ERROR(ArgumentCountMismatch);
+
   auto param = TRY(params.get(0));
   auto psize = TRY(param.size());
 
-  return Value(TRY(Int64::create((int64_t)psize)));
+  auto val = Value(TRY(Int64::create((int64_t)psize)));
+
+  auto res = TRY(stack.set(0, val));
+  return res.ret(0);
 }
 
 #define STDLIB_FUNCTION(name, id)                                  \
@@ -180,13 +215,13 @@ Result<StdlibFunctionId> get_stdlib_function(const Symbol& name) {
   return fun_id;
 }
 
-Result<Value> call_stdlib_function(StdlibFunctionId fun_id,
-                                   const Array& params) {
+Result<StackFrame> call_stdlib_function(StdlibFunctionId fun_id,
+                                        const StackFrame& stack) {
   if (fun_id == StdlibFunctionId(0) || fun_id >= StdlibFunctionId::Max) {
     return ERROR(KeyError);
   }
 
-  return function_entries[(uint64_t)fun_id].fun_ptr(params);
+  return function_entries[(uint64_t)fun_id].fun_ptr(stack);
 }
 
 Result<const char*> get_stdlib_function_name(StdlibFunctionId fun_id) {
diff --git a/src/stdlib.hpp b/src/stdlib.hpp
index 4c71ec6..c04fd9a 100644
--- a/src/stdlib.hpp
+++ b/src/stdlib.hpp
@@ -22,8 +22,9 @@ enum class StdlibFunctionId : uint64_t {
 class Value;
 class Symbol;
 class Array;
+class StackFrame;
 
 Result<const char*> get_stdlib_function_name(StdlibFunctionId fun_id);
 Result<StdlibFunctionId> get_stdlib_function(const Symbol& name);
-Result<Value> call_stdlib_function(StdlibFunctionId fun_id,
-                                   const Array& params);
+Result<StackFrame> call_stdlib_function(StdlibFunctionId fun_id,
+                                        const StackFrame& stack);
diff --git a/src/vm.cpp b/src/vm.cpp
index 7f57206..2a6535f 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -278,20 +278,11 @@ Result<void> VM::step_bytecode() {
 }
 
 Result<void> VM::step_native() {
-  // foo
   auto fun = TRY(_stack.fun());
   if (!fun.is<StdlibFunction>()) return ERROR(TypeMismatch);
   auto fun_id = fun.to<StdlibFunction>()->fun_id();
 
-  auto params = TRY(_stack.get(0));
-  if (!params.is<Array>()) return ERROR(TypeMismatch);
-
-  auto res = TRY(call_stdlib_function(fun_id, *params.to<Array>()));
-
-  auto top = TRY(_stack.size());
-  _stack = TRY(_stack.set(top, res));
-  _stack = TRY(_stack.ret(top));
-
+  _stack = TRY(call_stdlib_function(fun_id, _stack));
   _stack = TRY(_stack.incpc());
   return Result<void>();
 }