let dbhost = "localhost"; let dbname = "testdb"; let mk_db_conn = macro (host, port, db) => { conn_string = "@:@/@" % (host, port, db) host = host, port = port, db = db, }; let db_conn = mk_db_conn(host, 3306, dbame); let server_config = { dbconn = db_conn.conn_string, tmpldir = "./templates" };