diff --git a/Cargo.toml b/Cargo.toml
index 1970159..a7c89d8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,7 +27,8 @@ array_tool = "1.0.3"
 [lib]
 name = "jsonpath_lib"
 path = "src/lib.rs"
+crate-type = ["cdylib", "rlib"]
 
 [profile.release]
 #debug = true
-#lto = false
+#lto = false
\ No newline at end of file
diff --git a/benchmark/benches_lua_vs_rust/bench_lua_vs_rust.sh b/benchmark/benches_lua_vs_rust/bench_lua_vs_rust.sh
deleted file mode 100755
index dee47a0..0000000
--- a/benchmark/benches_lua_vs_rust/bench_lua_vs_rust.sh
+++ /dev/null
@@ -1,25 +0,0 @@
-#!/bin/bash
-
-set -e
-
-# http://luajit.org/index.html
-
-cargo clean && \
-cargo build --release
-
-export JSONPATH_LIB_PATH="${PWD}/../../target/release"
-export LUA_PATH="${PWD}/../../lua/?.lua;"
-
-echo
-time cargo run --release -- 1000
-echo
-time luajit example.lua 1000
-echo
-time cargo run --release -- 5000
-echo
-time luajit example.lua 5000
-echo
-time cargo run --release -- 10000
-echo
-time luajit example.lua 10000
-
diff --git a/benchmark/benches_lua_vs_rust/lib.rs b/benchmark/benches_lua_vs_rust/lib.rs
deleted file mode 100644
index e69de29..0000000
diff --git a/benchmark/benches_lua_vs_rust/.gitignore b/lua/.gitignore
similarity index 100%
rename from benchmark/benches_lua_vs_rust/.gitignore
rename to lua/.gitignore
diff --git a/benchmark/benches_lua_vs_rust/Cargo.toml b/lua/Cargo.toml
similarity index 66%
rename from benchmark/benches_lua_vs_rust/Cargo.toml
rename to lua/Cargo.toml
index a4523f2..fe05a10 100644
--- a/benchmark/benches_lua_vs_rust/Cargo.toml
+++ b/lua/Cargo.toml
@@ -1,13 +1,14 @@
 [package]
-name = "lua_vs_rust_benchmark"
+name = "jsonpath_lua"
 version = "0.1.0"
 authors = ["Changseok Han <freestrings@gmail.com>"]
 license = "MIT"
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0", features = ["preserve_order"] }
-jsonpath_lib = { path = "../../" }
+jsonpath_lib = { path = "../" }
 
 [[bin]]
-name = "lua_vs_rust_benchmark"
-path = "example.rs"
\ No newline at end of file
+name = "bench"
+path = "bench_lua_vs_rust/example.rs"
+
diff --git a/lua/bench_lua_vs_rust.sh b/lua/bench_lua_vs_rust.sh
new file mode 100755
index 0000000..668d7f5
--- /dev/null
+++ b/lua/bench_lua_vs_rust.sh
@@ -0,0 +1,25 @@
+#!/bin/bash
+
+set -e
+
+# http://luajit.org/index.html
+
+#cargo clean && \
+cargo build --release
+
+export JSONPATH_LIB_PATH="${PWD}/target/release/deps"
+export LUA_PATH="${PWD}/?.lua;"
+
+echo
+time cargo run --release --bin bench -- 1000
+echo
+time luajit bench_lua_vs_rust/example.lua 1000
+echo
+time cargo run --release --bin bench -- 5000
+echo
+time luajit bench_lua_vs_rust/example.lua 5000
+echo
+time cargo run --release --bin bench -- 10000
+echo
+time luajit bench_lua_vs_rust/example.lua 10000
+
diff --git a/benchmark/benches_lua_vs_rust/example.lua b/lua/bench_lua_vs_rust/example.lua
similarity index 62%
rename from benchmark/benches_lua_vs_rust/example.lua
rename to lua/bench_lua_vs_rust/example.lua
index 759ec9f..cd833da 100644
--- a/benchmark/benches_lua_vs_rust/example.lua
+++ b/lua/bench_lua_vs_rust/example.lua
@@ -9,12 +9,12 @@ end
 
 print(string.format("%s - %u", "lua iter", iter));
 
-local file = io.open("../../benchmark/example.json", "r");
+local file = io.open("../benchmark/example.json", "r");
 io.input(file)
 local data = io.read("*a");
 io.close(file);
-local cb = compile("$..book[?(@.price<30 && @.category==\"fiction\")]");
+local template = compile("$..book[?(@.price<30 && @.category==\"fiction\")]");
 for i = 0, iter do
-    local r = cb(data);
+    local r = template(data);
 --    print(r);
 end
diff --git a/benchmark/benches_lua_vs_rust/example.rs b/lua/bench_lua_vs_rust/example.rs
similarity index 95%
rename from benchmark/benches_lua_vs_rust/example.rs
rename to lua/bench_lua_vs_rust/example.rs
index 68f63b2..7c48910 100644
--- a/benchmark/benches_lua_vs_rust/example.rs
+++ b/lua/bench_lua_vs_rust/example.rs
@@ -14,7 +14,7 @@ fn read_json(path: &str) -> String {
 }
 
 fn get_string() -> String {
-    read_json("../../benchmark/example.json")
+    read_json("../benchmark/example.json")
 }
 
 fn get_json() -> Value {
diff --git a/lua/lib.lua b/lua/lib.lua
index 446b024..20eafd2 100644
--- a/lua/lib.lua
+++ b/lua/lib.lua
@@ -8,10 +8,10 @@ else
     ext = 'dylib'
 end
 
-ffi.cdef[[
+ffi.cdef [[
 const char* ffi_select(const char *json_str, const char *path);
 void *ffi_path_compile(const char *path);
-const char* ffi_select_with_compiled(void *ptr, const char *json_str);
+const char* ffi_select_with_compiled_path(void *ptr, const char *json_str);
 ]]
 
 local jsonpathLibPath = os.getenv("JSONPATH_LIB_PATH");
@@ -20,6 +20,6 @@ local jsonpath = ffi.load(jsonpathLibPath .. '/libjsonpath_lib.' .. ext);
 function compile(path)
     local compiledPath = jsonpath.ffi_path_compile(path);
     return function(jsonStr)
-        return ffi.string(jsonpath.ffi_select_with_compiled(compiledPath, jsonStr));
+        return ffi.string(jsonpath.ffi_select_with_compiled_path(compiledPath, jsonStr));
     end
 end
\ No newline at end of file
diff --git a/src/ffi/mod.rs b/src/ffi/mod.rs
new file mode 100644
index 0000000..ab160bb
--- /dev/null
+++ b/src/ffi/mod.rs
@@ -0,0 +1,57 @@
+use std::ffi::{CStr, CString};
+use std::os::raw::{c_char, c_void};
+
+use {parser, select, select_as_str};
+
+const INVALID_PATH: &str = "invalid path";
+const INVALID_JSON: &str = "invalud json";
+
+fn to_str(v: *const c_char, err_msg: &str) -> &str {
+    unsafe { CStr::from_ptr(v) }.to_str().expect(err_msg)
+}
+
+fn to_char_ptr(v: &str) -> *const c_char {
+    let s = CString::new(v).expect(&format!("invalid string: {}", v));
+    let ptr = s.as_ptr();
+    std::mem::forget(s);
+    ptr
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_select(json_str: *const c_char, path: *const c_char) -> *const c_char {
+    let json_str = to_str(json_str, INVALID_JSON);
+    let path = to_str(path, INVALID_PATH);
+    match select_as_str(json_str, path) {
+        Ok(v) => to_char_ptr(v.as_str()),
+        Err(e) => {
+            panic!("{:?}", e);
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_path_compile(path: *const c_char) -> *mut c_void {
+    let path = to_str(path, INVALID_PATH);
+    let ref_node = Box::into_raw(Box::new(parser::Parser::compile(path).unwrap()));
+    let ptr = ref_node as *mut c_void;
+    std::mem::forget(ref_node);
+    ptr
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_select_with_compiled_path(
+    path_ptr: *mut c_void,
+    json_ptr: *const c_char,
+) -> *const c_char {
+    let node = unsafe { Box::from_raw(path_ptr as *mut parser::Node) };
+    let json_str = to_str(json_ptr, INVALID_JSON);
+    let json = serde_json::from_str(json_str).expect(&format!("invalid json string: {}", json_str));
+
+    let mut selector = select::Selector::default();
+    let found = selector.compiled_path(&node).value(&json).select().unwrap();
+    std::mem::forget(node);
+
+    let result =
+        serde_json::to_string(&found).expect(&format!("json serialize error: {:?}", found));
+    to_char_ptr(result.as_str())
+}
diff --git a/src/lib.rs b/src/lib.rs
index f2a138e..355a1a6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -135,9 +135,9 @@ use serde_json::Value;
 pub use parser::Parser;
 pub use select::JsonPathError;
 pub use select::{Selector, SelectorMut};
-use std::ffi::{CStr, CString};
-use std::os::raw::{c_char, c_void};
 
+#[doc(hidden)]
+mod ffi;
 #[doc(hidden)]
 mod parser;
 #[doc(hidden)]
@@ -468,71 +468,3 @@ where
     let value = selector.str_path(path)?.value(value).replace_with(fun)?;
     Ok(value.take().unwrap_or(Value::Null))
 }
-
-
-#[no_mangle]
-pub extern "C" fn ffi_select(json_str: *const c_char, path: *const c_char) -> *const c_char {
-    let json_str = match unsafe { CStr::from_ptr(json_str) }.to_str() {
-        Ok(s) => s,
-        Err(e) => {
-            panic!("{:?}", e);
-        }
-    };
-
-    let path = match unsafe { CStr::from_ptr(path) }.to_str() {
-        Ok(s) => s,
-        Err(e) => {
-            panic!("{:?}", e);
-        }
-    };
-
-    match select_as_str(json_str, path) {
-        Ok(v) => match serde_json::to_string(&v) {
-            Ok(s) => {
-                let s = CString::new(s.as_str()).unwrap();
-                let p = s.as_ptr();
-                std::mem::forget(s);
-                p
-            }
-            Err(e) => {
-                panic!("{:?}", e);
-            }
-        },
-        Err(e) => {
-            panic!("{:?}", e);
-        }
-    }
-}
-
-
-#[no_mangle]
-pub extern "C" fn ffi_path_compile(path: *const c_char) -> *mut c_void {
-    let path = match unsafe { CStr::from_ptr(path) }.to_str() {
-        Ok(s) => s,
-        Err(e) => {
-            panic!("{:?}", e);
-        }
-    };
-
-    Box::into_raw(Box::new(Parser::compile(path).unwrap())) as *mut c_void
-}
-
-#[no_mangle]
-pub extern "C" fn ffi_select_with_compiled(
-    path_ptr: *mut c_void,
-    json_ptr: *const c_char,
-) -> *const c_char {
-    let node = unsafe { Box::from_raw(path_ptr as *mut parser::Node) };
-    let json_str = unsafe { CStr::from_ptr(json_ptr) }.to_str().expect("invalid 'json_ptr' input");
-    let json = serde_json::from_str(json_str).expect(&format!("invalid json string: {}", json_str));
-
-    let mut selector = Selector::default();
-    let found = selector.compiled_path(&node).value(&json).select().unwrap();
-    std::mem::forget(node);
-
-    let result = serde_json::to_string(&found).expect(&format!("json serialize error: {:?}", found));
-    let result_cstring = CString::new(result.as_str()).expect(&format!("empty result: {:?}", result));
-    let result_ptr = result_cstring.as_ptr();
-    std::mem::forget(result_cstring);
-    result_ptr
-}
diff --git a/src/select/mod.rs b/src/select/mod.rs
index ca2fc4d..56c4efe 100644
--- a/src/select/mod.rs
+++ b/src/select/mod.rs
@@ -2,10 +2,10 @@ use std::collections::HashSet;
 use std::fmt;
 
 use array_tool::vec::{Intersect, Union};
+use serde_json::map::Entry;
 use serde_json::{Number, Value};
 
 use parser::*;
-use serde_json::map::Entry;
 
 fn to_f64(n: &Number) -> f64 {
     if n.is_i64() {