diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6f61887..3a9650f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,6 +3,7 @@ include_directories(.)
 add_definitions("-std=c++1y")
 
 add_executable(peglint lint/peglint.cc)
+add_executable(playground lint/playground/main.cc)
 add_executable(test-main test/test.cc)
 
 add_executable(calc example/calc.cc)
diff --git a/lint/playground/httplib.h b/lint/playground/httplib.h
new file mode 100644
index 0000000..69fe6d0
--- /dev/null
+++ b/lint/playground/httplib.h
@@ -0,0 +1,959 @@
+//
+//  httplib.h
+//
+//  Copyright (c) 2012 Yuji Hirose. All rights reserved.
+//  The Boost Software License 1.0
+//
+
+#ifndef _CPPHTTPLIB_HTTPSLIB_H_
+#define _CPPHTTPLIB_HTTPSLIB_H_
+
+#ifdef _MSC_VER
+#define _CRT_SECURE_NO_WARNINGS
+#define _CRT_NONSTDC_NO_DEPRECATE
+
+#ifndef SO_SYNCHRONOUS_NONALERT
+#define SO_SYNCHRONOUS_NONALERT 0x20;
+#endif
+#ifndef SO_OPENTYPE
+#define SO_OPENTYPE 0x7008
+#endif
+#ifndef snprintf
+#define snprintf _snprintf_s
+#endif
+
+#define S_ISREG(m)  (((m)&S_IFREG)==S_IFREG)
+#define S_ISDIR(m)  (((m)&S_IFDIR)==S_IFDIR)
+
+#include <fcntl.h>
+#include <io.h>
+#include <winsock2.h>
+#include <ws2tcpip.h>
+
+#undef min
+#undef max
+
+typedef SOCKET socket_t;
+#else
+#include <pthread.h>
+#include <unistd.h>
+#include <netdb.h>
+#include <cstring>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+typedef int socket_t;
+#endif
+
+#include <fstream>
+#include <functional>
+#include <map>
+#include <memory>
+#include <regex>
+#include <string>
+#include <sys/stat.h>
+#include <assert.h>
+
+namespace httplib
+{
+
+typedef std::map<std::string, std::string>      Map;
+typedef std::multimap<std::string, std::string> MultiMap;
+typedef std::smatch                             Match;
+
+struct Request {
+    std::string method;
+    std::string url;
+    MultiMap    headers;
+    std::string body;
+    Map         params;
+    Match       matches;
+
+    bool has_header(const char* key) const;
+    std::string get_header_value(const char* key) const;
+    void set_header(const char* key, const char* val);
+
+    bool has_param(const char* key) const;
+};
+
+struct Response {
+    int         status;
+    MultiMap    headers;
+    std::string body;
+
+    bool has_header(const char* key) const;
+    std::string get_header_value(const char* key) const;
+    void set_header(const char* key, const char* val);
+
+    void set_redirect(const char* url);
+    void set_content(const char* s, size_t n, const char* content_type);
+    void set_content(const std::string& s, const char* content_type);
+
+    Response() : status(-1) {}
+};
+
+class Server {
+public:
+    typedef std::function<void (const Request&, Response&)> Handler;
+    typedef std::function<void (const Request&, const Response&)> Logger;
+
+    Server();
+
+    void get(const char* pattern, Handler handler);
+    void post(const char* pattern, Handler handler);
+
+    bool set_base_dir(const char* path);
+
+    void set_error_handler(Handler handler);
+    void set_logger(Logger logger);
+
+    bool listen(const char* host, int port);
+    void stop();
+
+private:
+    typedef std::vector<std::pair<std::regex, Handler>> Handlers;
+
+    void process_request(FILE* fp_read, FILE* fp_write);
+    bool read_request_line(FILE* fp, Request& req);
+    bool routing(Request& req, Response& res);
+    bool handle_file_request(Request& req, Response& res);
+    bool dispatch_request(Request& req, Response& res, Handlers& handlers);
+
+    socket_t    svr_sock_;
+    std::string base_dir_;
+    Handlers    get_handlers_;
+    Handlers    post_handlers_;
+    Handler     error_handler_;
+    Logger      logger_;
+};
+
+class Client {
+public:
+    Client(const char* host, int port);
+
+    std::shared_ptr<Response> get(const char* url);
+    std::shared_ptr<Response> head(const char* url);
+    std::shared_ptr<Response> post(const char* url, const std::string& body, const char* content_type);
+    std::shared_ptr<Response> post(const char* url, const Map& params);
+
+    bool send(const Request& req, Response& res);
+
+private:
+    bool read_response_line(FILE* fp, Response& res);
+
+    const std::string host_;
+    const int         port_;
+};
+
+// Implementation
+namespace detail {
+
+template <class Fn>
+void split(const char* b, const char* e, char d, Fn fn)
+{
+    int i = 0;
+    int beg = 0;
+
+    while (e ? (b + i != e) : (b[i] != '\0')) {
+        if (b[i] == d) {
+            fn(&b[beg], &b[i]);
+            beg = i + 1;
+        }
+        i++;
+    }
+
+    if (i) {
+        fn(&b[beg], &b[i]);
+    }
+}
+
+template <typename T>
+inline bool read_and_close_socket(socket_t sock, T callback)
+{
+    FILE* fp_read;
+    FILE* fp_write;
+#ifdef _MSC_VER
+    int osfhandle = _open_osfhandle(sock, _O_RDONLY);
+    fp_read = _fdopen(osfhandle, "rb");
+    fp_write = _fdopen(osfhandle, "wb");
+#else
+    fp_read = fdopen(sock, "rb");
+    fp_write = fdopen(sock, "wb");
+#endif
+
+    auto ret = callback(fp_read, fp_write);
+
+#ifdef _MSC_VER
+    sock = osfhandle;
+#else
+    fclose(fp_read);
+    fclose(fp_write);
+#endif
+
+    return ret;
+}
+
+inline int shutdown_socket(socket_t sock)
+{
+#ifdef _MSC_VER
+    return shutdown(sock, SD_BOTH);
+#else
+    return shutdown(sock, SHUT_RDWR);
+#endif
+}
+
+inline int close_socket(socket_t sock)
+{
+#ifdef _MSC_VER
+    return closesocket(sock);
+#else
+    return close(sock);
+#endif
+}
+
+template <typename Fn>
+socket_t create_socket(const char* host, int port, Fn fn)
+{
+#ifdef _MSC_VER
+    int opt = SO_SYNCHRONOUS_NONALERT;
+    setsockopt(INVALID_SOCKET, SOL_SOCKET, SO_OPENTYPE, (char*)&opt, sizeof(opt));
+#endif
+
+    // Get address info
+    struct addrinfo hints;
+    struct addrinfo *result;
+
+    memset(&hints, 0, sizeof(struct addrinfo));
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+    hints.ai_flags = 0;
+    hints.ai_protocol = 0;
+
+    auto service = std::to_string(port);
+
+    if (getaddrinfo(host, service.c_str(), &hints, &result)) {
+        return -1;
+    }
+
+    for (auto rp = result; rp; rp = rp->ai_next) {
+       // Create a socket
+       auto sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
+       if (sock == -1) {
+          continue;
+       }
+
+       // Make 'reuse address' option available
+       int yes = 1;
+       setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char*)&yes, sizeof(yes));
+
+       // bind or connect
+       if (fn(sock, *rp)) {
+          freeaddrinfo(result);
+          return sock;
+       }
+
+       close_socket(sock);
+    }
+
+    freeaddrinfo(result);
+    return -1;
+}
+
+inline socket_t create_server_socket(const char* host, int port)
+{
+    return create_socket(host, port, [](socket_t sock, struct addrinfo& ai) -> socket_t {
+        if (::bind(sock, ai.ai_addr, ai.ai_addrlen)) {
+              return false;
+        }
+        if (listen(sock, 5)) { // Listen through 5 channels
+            return false;
+        }
+        return true;
+    });
+}
+
+inline socket_t create_client_socket(const char* host, int port)
+{
+    return create_socket(host, port, [](socket_t sock, struct addrinfo& ai) -> socket_t {
+        if (connect(sock, ai.ai_addr, ai.ai_addrlen)) {
+            return false;
+        }
+        return true;
+    });
+}
+
+inline bool is_file(const std::string& s)
+{
+    struct stat st;
+    return stat(s.c_str(), &st) >= 0 && S_ISREG(st.st_mode);
+}
+
+inline bool is_dir(const std::string& s)
+{
+    struct stat st;
+    return stat(s.c_str(), &st) >= 0 && S_ISDIR(st.st_mode);
+}
+
+inline void read_file(const std::string& path, std::string& out)
+{
+    auto fs = std::ifstream(path, std::ios_base::binary);
+    fs.seekg(0, std::ios_base::end);
+    auto size = fs.tellg();
+    fs.seekg(0);
+   out.resize(size);
+    fs.read(&out[0], size);
+}
+
+inline std::string get_file_extention(const std::string& path)
+{
+    std::smatch m;
+    auto pat = std::regex("\\.([a-zA-Z0-9]+)$");
+    auto ret = std::regex_search(path, m, pat);
+    std::string content_type;
+    if (ret) {
+        return m[1].str();
+    }
+    return std::string();
+}
+
+inline const char* get_content_type_from_file_extention(const std::string& ext)
+{
+    if (ext == "html") {
+        return "text/html";
+    }
+    return "text/plain";
+}
+
+inline const char* status_message(int status)
+{
+    switch (status) {
+    case 200: return "OK";
+    case 400: return "Bad Request";
+    case 404: return "Not Found";
+    default:
+        case 500: return "Internal Server Error";
+    }
+}
+
+inline const char* get_header_value(const MultiMap& map, const char* key, const char* def)
+{
+    auto it = map.find(key);
+    if (it != map.end()) {
+        return it->second.c_str();
+    }
+    return def;
+}
+
+inline int get_header_value_int(const MultiMap& map, const char* key, int def)
+{
+    auto it = map.find(key);
+    if (it != map.end()) {
+        return std::stoi(it->second);
+    }
+    return def;
+}
+
+inline bool read_headers(FILE* fp, MultiMap& headers)
+{
+    static std::regex re("(.+?): (.+?)\r\n");
+
+    const auto BUFSIZ_HEADER = 2048;
+    char buf[BUFSIZ_HEADER];
+
+    for (;;) {
+        if (!fgets(buf, BUFSIZ_HEADER, fp)) {
+            return false;
+        }
+        if (!strcmp(buf, "\r\n")) {
+            break;
+        }
+        std::cmatch m;
+        if (std::regex_match(buf, m, re)) {
+            auto key = std::string(m[1]);
+            auto val = std::string(m[2]);
+            headers.insert(std::make_pair(key, val));
+        }
+    }
+
+    return true;
+}
+
+template <typename T>
+bool read_content(T& x, FILE* fp)
+{
+    auto len = get_header_value_int(x.headers, "Content-Length", 0);
+    if (len) {
+        x.body.assign(len, 0);
+        if (!fread(&x.body[0], x.body.size(), 1, fp)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+template <typename T>
+inline void write_headers(FILE* fp, const T& res)
+{
+    fprintf(fp, "Connection: close\r\n");
+
+    for (const auto& x: res.headers) {
+        if (x.first != "Content-Type" && x.first != "Content-Length") {
+            fprintf(fp, "%s: %s\r\n", x.first.c_str(), x.second.c_str());
+        }
+    }
+
+    auto t = get_header_value(res.headers, "Content-Type", "text/plain");
+    fprintf(fp, "Content-Type: %s\r\n", t);
+    fprintf(fp, "Content-Length: %ld\r\n", res.body.size());
+    fprintf(fp, "\r\n");
+}
+
+inline void write_response(FILE* fp, const Request& req, const Response& res)
+{
+    fprintf(fp, "HTTP/1.0 %d %s\r\n", res.status, status_message(res.status));
+
+    write_headers(fp, res);
+
+    if (!res.body.empty() && req.method != "HEAD") {
+        fprintf(fp, "%s", res.body.c_str());
+    }
+}
+
+inline std::string encode_url(const std::string& s)
+{
+    std::string result;
+
+    for (auto i = 0; s[i]; i++) {
+        switch (s[i]) {
+        case ' ':  result += "+"; break;
+        case '\'': result += "%27"; break;
+        case ',':  result += "%2C"; break;
+        case ':':  result += "%3A"; break;
+        case ';':  result += "%3B"; break;
+        default:
+            if (s[i] < 0) {
+                result += '%';
+                char hex[4];
+                size_t len = snprintf(hex, sizeof(hex), "%02X", (unsigned char)s[i]);
+                assert(len == 2);
+                result.append(hex, len);
+            } else {
+                result += s[i];
+            }
+            break;
+        }
+   }
+
+    return result;
+}
+
+inline bool is_hex(char c, int& v)
+{
+    if (0x20 <= c && isdigit(c)) {
+        v = c - '0';
+        return true;
+    } else if ('A' <= c && c <= 'F') {
+        v = c - 'A' + 10;
+        return true;
+    } else if ('a' <= c && c <= 'f') {
+        v = c - 'a' + 10;
+        return true;
+    }
+    return false;
+}
+
+inline int from_hex_to_i(const std::string& s, int i, int cnt, int& val)
+{
+    val = 0;
+    for (; s[i] && cnt; i++, cnt--) {
+        int v = 0;
+        if (is_hex(s[i], v)) {
+            val = val * 16 + v;
+        } else {
+            break;
+        }
+    }
+    return --i;
+}
+
+inline size_t to_utf8(int code, char* buff)
+{
+    if (code < 0x0080) {
+        buff[0] = (code & 0x7F);
+        return 1;
+    } else if (code < 0x0800) {
+        buff[0] = (0xC0 | ((code >> 6) & 0x1F));
+        buff[1] = (0x80 | (code & 0x3F));
+        return 2;
+    } else if (code < 0xD800) {
+        buff[0] = (0xE0 | ((code >> 12) & 0xF));
+        buff[1] = (0x80 | ((code >> 6) & 0x3F));
+        buff[2] = (0x80 | (code & 0x3F));
+        return 3;
+    } else if (code < 0xE000)  { // D800 - DFFF is invalid...
+        return 0;
+    } else if (code < 0x10000) {
+        buff[0] = (0xE0 | ((code >> 12) & 0xF));
+        buff[1] = (0x80 | ((code >> 6) & 0x3F));
+        buff[2] = (0x80 | (code & 0x3F));
+        return 3;
+    } else if (code < 0x110000) {
+        buff[0] = (0xF0 | ((code >> 18) & 0x7));
+        buff[1] = (0x80 | ((code >> 12) & 0x3F));
+        buff[2] = (0x80 | ((code >> 6) & 0x3F));
+        buff[3] = (0x80 | (code & 0x3F));
+        return 4;
+    }
+
+    // NOTREACHED
+    return 0;
+}
+
+inline std::string decode_url(const std::string& s)
+{
+    std::string result;
+
+    for (int i = 0; s[i]; i++) {
+        if (s[i] == '%') {
+            i++;
+            assert(s[i]);
+
+            if (s[i] == '%') {
+                result += s[i];
+            } else if (s[i] == 'u') {
+                // Unicode
+                i++;
+                assert(s[i]);
+
+                int val = 0;
+                i = from_hex_to_i(s, i, 4, val);
+
+                char buff[4];
+                size_t len = to_utf8(val, buff);
+
+                if (len > 0) {
+                    result.append(buff, len);
+                }
+            } else {
+                // HEX
+                int val = 0;
+                i = from_hex_to_i(s, i, 2, val);
+                result += val;
+            }
+        } else if (s[i] == '+') {
+            result += ' ';
+        } else {
+            result += s[i];
+        }
+    }
+
+    return result;
+}
+
+inline void write_request(FILE* fp, const Request& req)
+{
+    auto url = encode_url(req.url);
+    fprintf(fp, "%s %s HTTP/1.0\r\n", req.method.c_str(), url.c_str());
+
+    write_headers(fp, req);
+
+    if (!req.body.empty()) {
+        if (req.has_header("application/x-www-form-urlencoded")) {
+            fprintf(fp, "%s", encode_url(req.body).c_str());
+        } else {
+            fprintf(fp, "%s", req.body.c_str());
+        }
+    }
+}
+
+inline void parse_query_text(const std::string& s, Map& params)
+{
+    split(&s[0], &s[s.size()], '&', [&](const char* b, const char* e) {
+        std::string key;
+        std::string val;
+        split(b, e, '=', [&](const char* b, const char* e) {
+            if (key.empty()) {
+                key.assign(b, e);
+            } else {
+                val.assign(b, e);
+            }
+        });
+        params[key] = detail::decode_url(val);
+    });
+}
+
+#ifdef _MSC_VER
+class WSInit {
+public:
+    WSInit::WSInit() {
+        WSADATA wsaData;
+        WSAStartup(0x0002, &wsaData);
+    }
+
+    WSInit::~WSInit() {
+        WSACleanup();
+    }
+};
+
+static WSInit wsinit_;
+#endif
+
+} // namespace detail
+
+// Request implementation
+inline bool Request::has_header(const char* key) const
+{
+    return headers.find(key) != headers.end();
+}
+
+inline std::string Request::get_header_value(const char* key) const
+{
+    return detail::get_header_value(headers, key, "");
+}
+
+inline void Request::set_header(const char* key, const char* val)
+{
+    headers.insert(std::make_pair(key, val));
+}
+
+inline bool Request::has_param(const char* key) const
+{
+    return params.find(key) != params.end();
+}
+
+// Response implementation
+inline bool Response::has_header(const char* key) const
+{
+    return headers.find(key) != headers.end();
+}
+
+inline std::string Response::get_header_value(const char* key) const
+{
+    return detail::get_header_value(headers, key, "");
+}
+
+inline void Response::set_header(const char* key, const char* val)
+{
+    headers.insert(std::make_pair(key, val));
+}
+
+inline void Response::set_redirect(const char* url)
+{
+    set_header("Location", url);
+    status = 302;
+}
+
+inline void Response::set_content(const char* s, size_t n, const char* content_type)
+{
+    body.assign(s, n);
+    set_header("Content-Type", content_type);
+}
+
+inline void Response::set_content(const std::string& s, const char* content_type)
+{
+    body = s;
+    set_header("Content-Type", content_type);
+}
+
+// HTTP server implementation
+inline Server::Server()
+    : svr_sock_(-1)
+{
+}
+
+inline void Server::get(const char* pattern, Handler handler)
+{
+    get_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+}
+
+inline void Server::post(const char* pattern, Handler handler)
+{
+    post_handlers_.push_back(std::make_pair(std::regex(pattern), handler));
+}
+
+inline bool Server::set_base_dir(const char* path)
+{
+    if (detail::is_dir(path)) {
+        base_dir_ = path;
+        return true;
+    }
+    return false;
+}
+
+inline void Server::set_error_handler(Handler handler)
+{
+    error_handler_ = handler;
+}
+
+inline void Server::set_logger(Logger logger)
+{
+    logger_ = logger;
+}
+
+inline bool Server::listen(const char* host, int port)
+{
+    svr_sock_ = detail::create_server_socket(host, port);
+    if (svr_sock_ == -1) {
+        return false;
+    }
+
+    auto ret = true;
+
+    for (;;) {
+        socket_t sock = accept(svr_sock_, NULL, NULL);
+
+        if (sock == -1) {
+            if (svr_sock_ != -1) {
+                detail::close_socket(svr_sock_);
+                ret = false;
+            } else {
+                ; // The server socket was closed by user.
+            }
+            break;
+        }
+
+        // TODO: should be async
+        detail::read_and_close_socket(sock, [this](FILE* fp_read, FILE* fp_write) {
+            process_request(fp_read, fp_write);
+            return true;
+        });
+    }
+
+    return ret;
+}
+
+inline void Server::stop()
+{
+    detail::shutdown_socket(svr_sock_);
+    detail::close_socket(svr_sock_);
+    svr_sock_ = -1;
+}
+
+inline bool Server::read_request_line(FILE* fp, Request& req)
+{
+    const auto BUFSIZ_REQUESTLINE = 2048;
+    char buf[BUFSIZ_REQUESTLINE];
+    if (!fgets(buf, BUFSIZ_REQUESTLINE, fp)) {
+        return false;
+    }
+
+    static std::regex re("(GET|HEAD|POST) ([^?]+)(?:\\?(.+?))? HTTP/1\\.[01]\r\n");
+
+    std::cmatch m;
+    if (std::regex_match(buf, m, re)) {
+        req.method = std::string(m[1]);
+        req.url = detail::decode_url(m[2]);
+
+        // Parse query text
+        auto len = std::distance(m[3].first, m[3].second);
+        if (len > 0) {
+            detail::parse_query_text(m[3], req.params);
+        }
+
+        return true;
+    }
+
+    return false;
+}
+
+inline bool Server::handle_file_request(Request& req, Response& res)
+{
+    if (!base_dir_.empty()) {
+        std::string path = base_dir_ + req.url;
+
+        if (!path.empty() && path.back() == '/') {
+            path += "index.html";
+        }
+
+        if (detail::is_file(path)) {
+            detail::read_file(path, res.body);
+            res.set_header("Content-Type", 
+                detail::get_content_type_from_file_extention(
+                    detail::get_file_extention(path)));
+            res.status = 200;
+            return true;
+        }
+    }
+
+    return false;
+}
+
+inline bool Server::routing(Request& req, Response& res)
+{
+    if (req.method == "GET" && handle_file_request(req, res)) {
+        return true;
+    }
+
+    if (req.method == "GET" || req.method == "HEAD") {
+        return dispatch_request(req, res, get_handlers_);
+    } else if (req.method == "POST") {
+        return dispatch_request(req, res, post_handlers_);
+    }
+    return false;
+}
+
+inline bool Server::dispatch_request(Request& req, Response& res, Handlers& handlers)
+{
+    for (const auto& x: handlers) {
+        const auto& pattern = x.first;
+        const auto& handler = x.second;
+
+        if (std::regex_match(req.url, req.matches, pattern)) {
+            handler(req, res);
+            return true;
+        }
+    }
+    return false;
+}
+
+inline void Server::process_request(FILE* fp_read, FILE* fp_write)
+{
+    Request req;
+    Response res;
+
+    if (!read_request_line(fp_read, req) ||
+        !detail::read_headers(fp_read, req.headers)) {
+        return;
+    }
+
+    if (req.method == "POST") {
+        if (!detail::read_content(req, fp_read)) {
+            return;
+        }
+        static std::string type = "application/x-www-form-urlencoded";
+        if (!req.get_header_value("Content-Type").compare(0, type.size(), type)) {
+            detail::parse_query_text(req.body, req.params);
+        }
+    }
+
+    if (routing(req, res)) {
+        if (res.status == -1) {
+            res.status = 200;
+        }
+    } else {
+        res.status = 404;
+    }
+    assert(res.status != -1);
+
+    if (400 <= res.status && error_handler_) {
+        error_handler_(req, res);
+    }
+
+    detail::write_response(fp_write, req, res);
+    fflush(fp_write);
+
+    if (logger_) {
+        logger_(req, res);
+    }
+}
+
+// HTTP client implementation
+inline Client::Client(const char* host, int port)
+    : host_(host)
+    , port_(port)
+{
+}
+
+inline bool Client::read_response_line(FILE* fp, Response& res)
+{
+    const auto BUFSIZ_RESPONSELINE = 2048;
+    char buf[BUFSIZ_RESPONSELINE];
+    if (!fgets(buf, BUFSIZ_RESPONSELINE, fp)) {
+        return false;
+    }
+
+    const static std::regex re("HTTP/1\\.[01] (\\d+?) .+\r\n");
+
+    std::cmatch m;
+    if (std::regex_match(buf, m, re)) {
+        res.status = std::stoi(std::string(m[1]));
+    }
+
+    return true;
+}
+
+inline bool Client::send(const Request& req, Response& res)
+{
+    auto sock = detail::create_client_socket(host_.c_str(), port_);
+    if (sock == -1) {
+        return false;
+    }
+
+    return detail::read_and_close_socket(sock, [&](FILE* fp_read, FILE* fp_write) {
+        // Send request
+        detail::write_request(fp_write, req);
+        fflush(fp_write);
+
+        // Receive response
+        if (!read_response_line(fp_read, res) ||
+            !detail::read_headers(fp_read, res.headers)) {
+            return false;
+        }
+        if (req.method != "HEAD") {
+            if (!detail::read_content(res, fp_read)) {
+                return false;
+            }
+        }
+
+        return true;
+    });
+}
+
+inline std::shared_ptr<Response> Client::get(const char* url)
+{
+    Request req;
+    req.method = "GET";
+    req.url = url;
+
+    auto res = std::make_shared<Response>();
+
+    return send(req, *res) ? res : nullptr;
+}
+
+inline std::shared_ptr<Response> Client::head(const char* url)
+{
+    Request req;
+    req.method = "HEAD";
+    req.url = url;
+
+    auto res = std::make_shared<Response>();
+
+    return send(req, *res) ? res : nullptr;
+}
+
+inline std::shared_ptr<Response> Client::post(
+    const char* url, const std::string& body, const char* content_type)
+{
+    Request req;
+    req.method = "POST";
+    req.url = url;
+    req.set_header("Content-Type", content_type);
+    req.body = body;
+
+    auto res = std::make_shared<Response>();
+
+    return send(req, *res) ? res : nullptr;
+}
+
+inline std::shared_ptr<Response> Client::post(
+    const char* url, const Map& params)
+{
+    std::string query;
+    for (auto it = params.begin(); it != params.end(); ++it) {
+        if (it != params.begin()) {
+            query += "&";
+        }
+        query += it->first;
+        query += "=";
+        query += it->second;
+    }
+
+    return post(url, query, "application/x-www-form-urlencoded");
+}
+
+} // namespace httplib
+
+#endif
+
+// vim: et ts=4 sw=4 cin cino={1s ff=unix
diff --git a/lint/playground/main.cc b/lint/playground/main.cc
new file mode 100644
index 0000000..9f857e4
--- /dev/null
+++ b/lint/playground/main.cc
@@ -0,0 +1,110 @@
+
+#include "httplib.h"
+#include "peglib.h"
+#include <cstdio>
+#include <functional>
+
+using namespace httplib;
+using namespace std;
+
+void open_url(const char* url)
+{
+    string cmd;
+#ifdef _MSC_VER
+    cmd += "start ";
+#else
+    cmd += "open ";
+#endif
+    cmd += url;
+    system(cmd.c_str());
+}
+
+function<void (size_t, size_t, const string&)> makeJSONFormatter(string& json)
+{
+    auto init = make_shared<bool>(true);
+
+    return [&json, init](size_t ln, size_t col, const string& msg) mutable {
+        if (!init) {
+            json += ",";
+        }
+        json += "{";
+        json += R"("ln":)" + to_string(ln) + ",";
+        json += R"("col":)" + to_string(col) + ",";
+        json += R"("msg":")" + msg + R"(")";
+        json += "}";
+        *init = false;
+    };
+}
+
+bool parse_grammar(const string& text, peglib::peg& peg, string& json)
+{
+    peg.log = makeJSONFormatter(json);
+    json += "[";
+    auto ret = peg.load_grammar(text.data(), text.size());
+    json += "]";
+    return ret;
+}
+
+bool parse_code(const string& text, peglib::peg& peg, string& json)
+{
+    peg.log = makeJSONFormatter(json);
+    json += "[";
+    auto ret = peg.parse_n(text.data(), text.size());
+    json += "]";
+    return ret;
+}
+
+int main(void)
+{
+    Server svr;
+
+    if (!svr.set_base_dir("./www")) {
+        cerr << "invalid 'www' directory." << endl;
+        return -1;
+    }
+
+    svr.post("/parse", [](const Request& req, Response& res) {
+        const auto& grammarText = req.params.at("grammar");
+
+        string grammarResult;
+        string codeResult;
+
+        peglib::peg peg;
+        auto ret = parse_grammar(grammarText, peg, grammarResult);
+
+        if (ret && peg) {
+            const auto& codeText = req.params.at("code");
+            parse_code(codeText, peg, codeResult);
+        }
+
+        string json;
+        json += "{";
+        json += "\"grammar\":" + grammarResult;
+        if (!codeResult.empty()) {
+            json += +",";
+            json += "\"code\":" + codeResult;
+        }
+        json += "}";
+
+        res.set_content(json, "application/json");
+    });
+
+    svr.get("/stop", [&](const Request& req, Response& res) {
+        svr.stop();
+    });
+
+    svr.set_error_handler([](const Request& req, Response& res) {
+        const char* fmt = "<p>Error Status: <span style='color:red;'>%d</span></p>";
+        char buf[BUFSIZ];
+        snprintf(buf, sizeof(buf), fmt, res.status);
+        res.set_content(buf, "text/html");
+    });
+
+    open_url("http://localhost:1234");
+
+    svr.listen("localhost", 1234);
+
+    return 0;
+}
+
+// vim: et ts=4 sw=4 cin cino={1s ff=unix
diff --git a/lint/playground/playground.sln b/lint/playground/playground.sln
new file mode 100644
index 0000000..7809f4a
--- /dev/null
+++ b/lint/playground/playground.sln
@@ -0,0 +1,26 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 2013
+VisualStudioVersion = 12.0.31101.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "playground", "playground.vcxproj", "{F85B641A-7538-4809-8175-C528FF632CF6}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Win32 = Debug|Win32
+		Release|Win32 = Release|Win32
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{F85B641A-7538-4809-8175-C528FF632CF6}.Debug|Win32.ActiveCfg = Debug|Win32
+		{F85B641A-7538-4809-8175-C528FF632CF6}.Debug|Win32.Build.0 = Debug|Win32
+		{F85B641A-7538-4809-8175-C528FF632CF6}.Release|Win32.ActiveCfg = Release|Win32
+		{F85B641A-7538-4809-8175-C528FF632CF6}.Release|Win32.Build.0 = Release|Win32
+		{1D09607B-E1C0-4D62-8AB4-9E2D2C2DC6E4}.Debug|Win32.ActiveCfg = Debug|Win32
+		{1D09607B-E1C0-4D62-8AB4-9E2D2C2DC6E4}.Debug|Win32.Build.0 = Debug|Win32
+		{1D09607B-E1C0-4D62-8AB4-9E2D2C2DC6E4}.Release|Win32.ActiveCfg = Release|Win32
+		{1D09607B-E1C0-4D62-8AB4-9E2D2C2DC6E4}.Release|Win32.Build.0 = Release|Win32
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+EndGlobal
diff --git a/lint/playground/playground.vcxproj b/lint/playground/playground.vcxproj
new file mode 100644
index 0000000..11b4075
--- /dev/null
+++ b/lint/playground/playground.vcxproj
@@ -0,0 +1,94 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <ItemGroup>
+    <ClCompile Include="main.cc" />
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="httplib.h" />
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="www\index.html" />
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>{F85B641A-7538-4809-8175-C528FF632CF6}</ProjectGuid>
+    <Keyword>Win32Proj</Keyword>
+    <ProjectName>playground</ProjectName>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v120</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+    <PlatformToolset>v120</PlatformToolset>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <LinkIncremental>true</LinkIncremental>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <LinkIncremental>false</LinkIncremental>
+  </PropertyGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <ClCompile>
+      <PrecompiledHeader>
+      </PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>Disabled</Optimization>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <AdditionalIncludeDirectories>../..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>Ws2_32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <PrecompiledHeader>
+      </PrecompiledHeader>
+      <Optimization>MaxSpeed</Optimization>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <AdditionalIncludeDirectories>../..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+      <AdditionalDependencies>Ws2_32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+    </Link>
+  </ItemDefinitionGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  </ImportGroup>
+</Project>
\ No newline at end of file
diff --git a/lint/playground/www/index.html b/lint/playground/www/index.html
new file mode 100644
index 0000000..dd9618c
--- /dev/null
+++ b/lint/playground/www/index.html
@@ -0,0 +1,193 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+<title>PEG Playground</title>
+<style>
+* {
+    box-sizing: border-box;
+    margin: 0;
+    padding: 0;
+    text-decoration: none;
+    list-style: none;
+}
+body {
+    display: flex;
+    flex-direction: column;
+    height: 100vh;
+}
+#main {
+    flex: 1;
+    display: none;
+}
+.editor-container {
+    flex: 1;
+    width: 100%;
+    display: flex;
+    flex-direction: column;
+    margin: 8px;
+}
+.editor-container:first-child {
+    margin-right: 0;
+}
+.editor-header {
+    display: flex;
+    height: 48px;
+    padding: 4px 8px;
+}
+.editor-header > li:last-child {
+    margin-left: auto;
+}
+.editor-header > li > span {
+    height: 38px;
+    line-height: 38px;
+}
+.editor-header > li > a {
+    height: 38px;
+    line-height: 38px;
+    padding: .3em .5em;
+    border: 1px solid red;
+}
+.editor-validation {
+    height: 38px;
+    line-height: 38px;
+    padding: .4em .6em;
+    color: green;
+    background-color: lightgreen;
+    border-radius: 5px;
+}
+.editor-validation-invalid {
+    color: red;
+    background-color: pink;
+}
+.editor-area {
+    flex: 1;
+    border: 1px solid lightgray;
+}
+.editor-info {
+    margin-top: 6px;
+    height: 160px;
+    border: 1px solid lightgray;
+    padding: 8px;
+}
+.editor-info li {
+    cursor: pointer;
+}
+</style>
+</head>
+<body>
+
+<div id="main">
+    <div class="editor-container">
+        <ul class="editor-header">
+            <li><span>Grammar:</span></li>
+            <li><span id="grammar-validation" class="editor-validation">Valid</span></li>
+        </ul>
+        <pre id="grammar-editor" class="editor-area">
+EXPRESSION       <-  _ TERM (TERM_OPERATOR TERM)*
+TERM             <-  FACTOR (FACTOR_OPERATOR FACTOR)*
+FACTOR           <-  NUMBER / '(' _ EXPRESSION ')' _
+TERM_OPERATOR    <-  < [-+] > _
+FACTOR_OPERATOR  <-  < [/*] > _
+NUMBER           <-  < [0-9]+ > _
+~_               <-  [ \t\r\n]*</pre>
+        <div id="grammar-info" class="editor-info"></div>
+    </div>
+    <div class="editor-container">
+        <ul class="editor-header">
+            <li><span>Code:</span></li>
+            <li><span id="code-validation" class="editor-validation">Valid</span></li>
+        </ul>
+        <pre id="code-editor"  class="editor-area">2 * (3 + 4)</pre>
+        <div id="code-info" class="editor-info"></div>
+    </div>
+</div>
+
+<script src="https://cdnjs.cloudflare.com/ajax/libs/ace/1.1.9/ace.js"></script>
+<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
+<script>
+	// Setup editros
+    var grammar = ace.edit("grammar-editor");
+    grammar.setShowPrintMargin(false);
+
+    var code = ace.edit("code-editor");
+    code.setShowPrintMargin(false);
+
+    var generateErrorListHTML = function (errors) {
+        var html = '<ul>';
+
+        html += $.map(errors, function (x) {
+            return '<li data-ln="' + x.ln + '" data-col="' + x.col + '"><span>' + x.ln + ':' + x.col + '</span> <span>' + x.msg + '</span></li>';
+        }).join('');
+
+        html += '<ul>';
+
+        return html;
+    };
+
+    var parse = function () {
+        var $grammarValidation = $('#grammar-validation');
+        var $grammarInfo = $('#grammar-info');
+        var grammarText = grammar.getValue();
+
+        var $codeValidation = $('#code-validation');
+        var $codeInfo = $('#code-info');
+        var codeText = code.getValue();
+
+        $.post("/parse", {
+            grammar: grammarText,
+            code: codeText
+        }).done(function (data) {
+            var isValid = data.grammar.length === 0;
+            if (isValid) {
+                $grammarInfo.html('');
+                $grammarValidation.removeClass('editor-validation-invalid').text('Valid');
+
+	            var isValid = data.code.length === 0;
+	            if (isValid) {
+	                $codeInfo.html('');
+	                $codeValidation.removeClass('editor-validation-invalid').text('Valid');
+	            } else {
+				    var html = generateErrorListHTML(data.code);
+	                $codeInfo.html(html);
+	                $codeValidation.addClass('editor-validation-invalid').text('Invalid');
+	            }
+                $codeValidation.show();
+            } else {
+			    var html = generateErrorListHTML(data.grammar);
+                $grammarInfo.html(html);
+                $grammarValidation.addClass('editor-validation-invalid').text('Invalid');
+
+                $codeValidation.hide();
+            }
+        });
+    };
+
+    // Event handing for text editiing
+    var timer;
+    var setupTimer = function () {
+        clearTimeout(timer);
+        timer = setTimeout(parse, 750);
+    };
+    grammar.getSession().on('change', setupTimer);
+    code.getSession().on('change', setupTimer);
+
+    // Event handing in the info area
+    var makeOnClickInInfo = function (editor) {
+    	return function () {
+	        var el = $(this);
+	        editor.navigateTo(el.data('ln') - 1, el.data('col') - 1);
+	        editor.focus();
+    	}
+    };
+    $('#grammar-info').on('click', 'li', makeOnClickInInfo(grammar));
+    $('#code-info').on('click', 'li', makeOnClickInInfo(code));
+
+    // Show page
+    $('#main').css('display', 'flex');
+
+    // Initial parse
+    parse();
+</script>
+</body>
+</html>
+