diff --git a/server/conn_context.h b/server/conn_context.h
index d832bbc..39e59cb 100644
--- a/server/conn_context.h
+++ b/server/conn_context.h
@@ -90,6 +90,12 @@ class ConnectionContext {
     return rbuilder_.get();
   }
 
+  ReplyBuilderInterface* Inject(ReplyBuilderInterface* new_i) {
+    ReplyBuilderInterface* res = rbuilder_.release();
+    rbuilder_.reset(new_i);
+    return res;
+  }
+
  private:
   Connection* owner_;
   std::unique_ptr<ReplyBuilderInterface> rbuilder_;
diff --git a/server/dragonfly_test.cc b/server/dragonfly_test.cc
index 0cb8858..6da3681 100644
--- a/server/dragonfly_test.cc
+++ b/server/dragonfly_test.cc
@@ -218,8 +218,11 @@ TEST_F(DflyEngineTest, Eval) {
   auto resp = Run({"eval", "return 43", "0"});
   EXPECT_THAT(resp[0], IntArg(43));
 
-  // resp = Run({"eval", "return redis.call('get', 'foo')", "0"});
-  // EXPECT_THAT(resp[0], IntArg(42));  // TODO.
+  resp = Run({"incrby", "foo", "42"});
+  EXPECT_THAT(resp[0], IntArg(42));
+
+  resp = Run({"eval", "return redis.call('get', 'foo')", "0"});
+  EXPECT_THAT(resp[0], StrArg("42"));
 }
 
 TEST_F(DflyEngineTest, EvalSha) {
diff --git a/server/main_service.cc b/server/main_service.cc
index 7cd7634..4244884 100644
--- a/server/main_service.cc
+++ b/server/main_service.cc
@@ -50,6 +50,39 @@ metrics::CounterFamily cmd_req("requests_total", "Number of served redis request
 
 constexpr size_t kMaxThreadSize = 1024;
 
+class InterpreterReplier : public RedisReplyBuilder {
+ public:
+  InterpreterReplier(ObjectExplorer* explr) : RedisReplyBuilder(nullptr), explr_(explr) {
+  }
+
+  void SendError(std::string_view str) override;
+  void SendGetReply(std::string_view key, uint32_t flags, std::string_view value) override;
+  void SendGetNotFound() override;
+  void SendStored() override;
+
+  void SendSimpleString(std::string_view str) final;
+  void SendMGetResponse(const StrOrNil* arr, uint32_t count) final;
+  void SendSimpleStrArr(const std::string_view* arr, uint32_t count) final;
+  void SendNullArray() final;
+
+  void SendStringArr(absl::Span<const std::string_view> arr) final;
+  void SendNull() final;
+
+  void SendLong(long val) final;
+  void SendDouble(double val) final;
+
+  void SendBulkString(std::string_view str) final;
+
+  void StartArray(unsigned len) final;
+
+ private:
+  void PostItem();
+
+  ObjectExplorer* explr_;
+  vector<pair<unsigned, unsigned>> array_len_;
+  unsigned num_elems_ = 0;
+};
+
 class EvalSerializer : public ObjectExplorer {
  public:
   EvalSerializer(RedisReplyBuilder* rb) : rb_(rb) {
@@ -63,7 +96,7 @@ class EvalSerializer : public ObjectExplorer {
     }
   }
 
-  void OnString(std::string_view str) final {
+  void OnString(string_view str) final {
     rb_->SendBulkString(str);
   }
 
@@ -87,11 +120,11 @@ class EvalSerializer : public ObjectExplorer {
     rb_->SendNull();
   }
 
-  void OnStatus(std::string_view str) {
+  void OnStatus(string_view str) {
     rb_->SendSimpleString(str);
   }
 
-  void OnError(std::string_view str) {
+  void OnError(string_view str) {
     rb_->SendError(str);
   }
 
@@ -99,6 +132,117 @@ class EvalSerializer : public ObjectExplorer {
   RedisReplyBuilder* rb_;
 };
 
+void InterpreterReplier::PostItem() {
+  if (array_len_.empty()) {
+    DCHECK_EQ(0u, num_elems_);
+    ++num_elems_;
+  } else {
+    ++num_elems_;
+
+    while (num_elems_ == array_len_.back().second) {
+      num_elems_ = array_len_.back().first;
+      explr_->OnArrayEnd();
+
+      array_len_.pop_back();
+      if (array_len_.empty())
+        break;
+    }
+  }
+}
+
+void InterpreterReplier::SendError(string_view str) {
+  DCHECK(array_len_.empty());
+  explr_->OnError(str);
+}
+
+void InterpreterReplier::SendGetReply(string_view key, uint32_t flags, string_view value) {
+  DCHECK(array_len_.empty());
+  explr_->OnString(value);
+}
+
+void InterpreterReplier::SendGetNotFound() {
+  DCHECK(array_len_.empty());
+  explr_->OnNil();
+}
+
+void InterpreterReplier::SendStored() {
+  DCHECK(array_len_.empty());
+  SendSimpleString("OK");
+}
+
+void InterpreterReplier::SendSimpleString(string_view str) {
+  if (array_len_.empty())
+    explr_->OnStatus(str);
+  else
+    explr_->OnString(str);
+  PostItem();
+}
+
+void InterpreterReplier::SendMGetResponse(const StrOrNil* arr, uint32_t count) {
+  DCHECK(array_len_.empty());
+
+  explr_->OnArrayStart(count);
+  for (uint32_t i = 0; i < count; ++i) {
+    if (arr[i].has_value()) {
+      explr_->OnString(*arr[i]);
+    } else {
+      explr_->OnNil();
+    }
+  }
+  explr_->OnArrayEnd();
+}
+
+void InterpreterReplier::SendSimpleStrArr(const string_view* arr, uint32_t count) {
+  explr_->OnArrayStart(count);
+  for (uint32_t i = 0; i < count; ++i) {
+    explr_->OnString(arr[i]);
+  }
+  explr_->OnArrayEnd();
+  PostItem();
+}
+
+void InterpreterReplier::SendNullArray() {
+  SendSimpleStrArr(nullptr, 0);
+  PostItem();
+}
+
+void InterpreterReplier::SendStringArr(absl::Span<const string_view> arr) {
+  SendSimpleStrArr(arr.data(), arr.size());
+  PostItem();
+}
+
+void InterpreterReplier::SendNull() {
+  explr_->OnNil();
+  PostItem();
+}
+
+void InterpreterReplier::SendLong(long val) {
+  explr_->OnInt(val);
+  PostItem();
+}
+
+void InterpreterReplier::SendDouble(double val) {
+  explr_->OnDouble(val);
+  PostItem();
+}
+
+void InterpreterReplier::SendBulkString(string_view str) {
+  explr_->OnString(str);
+  PostItem();
+}
+
+void InterpreterReplier::StartArray(unsigned len) {
+  explr_->OnArrayStart(len);
+
+  if (len == 0) {
+    explr_->OnArrayEnd();
+    PostItem();
+  } else {
+    array_len_.emplace_back(num_elems_ + 1, len);
+    num_elems_ = 0;
+  }
+}
+
 bool IsSHA(string_view str) {
   for (auto c : str) {
     if (!absl::ascii_isxdigit(c))
@@ -355,8 +499,12 @@ void Service::Multi(CmdArgList args, ConnectionContext* cntx) {
 }
 
 void Service::CallFromScript(CmdArgList args, ObjectExplorer* reply, ConnectionContext* cntx) {
-  // reply->OnInt(42);
+  InterpreterReplier replier(reply);
+  ReplyBuilderInterface* orig = cntx->Inject(&replier);
+
   DispatchCommand(std::move(args), cntx);
+
+  cntx->Inject(orig);
 }
 
 void Service::Eval(CmdArgList args, ConnectionContext* cntx) {
@@ -475,7 +623,7 @@ void Service::EvalInternal(const EvalArgs& eval_args, Interpreter* interpreter,
 
   Interpreter::RunResult result = interpreter->RunFunction(eval_args.sha, &error);
 
-  cntx->conn_state.script_info.reset(); // reset script_info
+  cntx->conn_state.script_info.reset();  // reset script_info
 
   if (result == Interpreter::RUN_ERR) {
     string resp = absl::StrCat("Error running script (call to ", eval_args.sha, "): ", error);
diff --git a/server/reply_builder.cc b/server/reply_builder.cc
index 37cf972..ffc8e00 100644
--- a/server/reply_builder.cc
+++ b/server/reply_builder.cc
@@ -36,6 +36,8 @@ void SinkReplyBuilder::CloseConnection() {
 }
 
 void SinkReplyBuilder::Send(const iovec* v, uint32_t len) {
+  DCHECK(sink_);
+
   if (should_batch_) {
     // TODO: to introduce flushing when too much data is batched.
     for (unsigned i = 0; i < len; ++i) {