/// <summary>
/// Creates new grammar.
/// </summary>
/// <returns>
/// When resolved, a newly created <see cref="Grammar" /> object. When rejected, an
/// <see cref="Exception" /> with info about error that occured.
/// </returns>
public static IPromise <Grammar> CreateGrammar()
{
return(WebAPI.CreateGrammar()
.Then(grammar => {
grammarList.Add(grammar.id, grammar);
SaveGrammarList();
return grammar;
}));
}