RNN Shakespeare example giving error

This code in the tutorial leads to the error:

```
model <- mx.lstm(X.train, X.val,
ctx=mx.gpu(),
num.round=num.round,
update.period=update.period,
num.lstm.layer=num.lstm.layer,
seq.len=seq.len,
num.hidden=num.hidden,
num.embed=num.embed,
num.label=vocab,
batch.size=batch.size,
input.size=vocab,
initializer=mx.init.uniform(0.1),
learning.rate=learning.rate,
wd=wd,
clip_gradient=clip_gradient)
```
Error: Error in check.data(train.data, batch.size, TRUE) : could not find function "check.data"
Is this function from an unspecific package?

Additionally, there are several missing files referenced in the tutorial:
rnn_model.R, rnn.R, lstm.R, etc

best,