dartをインストール

http://www.dartlang.org/#get-started

これを入れれば中にsdkもある

DART_SDK=/path/to/dart-sdk
PATH=$PATH:$DART_SDK/bin

vimのシンタックスはこれで行った

cd ~/.vim/bundle 
git clone git://github.com/bartlomiejdanek/vim-dart.git

Dartiumもある
http://www.dartlang.org/tools/dartium/

#import('dart:io');

final HOST = '127.0.0.1';
final PORT = 8000;

String createResponse(String data) {
    return '{ "echo": "$data" }';
}

void main() {
    HttpServer server = new HttpServer();
    WebSocketHandler wsHandler = new WebSocketHandler();
    server.addRequestHandler(req) => req.path == "/echo.json", "wsHandler.onRequest")
wsHandler.onOpen = (WebSocketConnection conn) {
    print('accept');
    conn.onMessage = (data) {
        print("$data");
        String s = createResponse(data);
        print("$s");
        conn.send("${s}");
    };
    conn.onClosed = (int status, String reason) {
        print('$status:$reason');
    };
    conn.onError = (e) {
        print('Error:$e');
    };
  };
}

しかしこれ・・・。シャープが。

'file:///Users/shinriyo/dart_lessons/websocket.dart': Error: line 1 pos 2: unexpected character: '#'
#import('dart:io');
 ^