Exactly. Data is necessary to make control flow decisions; the purely behavioural approach suffers infinite regress without some form of concrete data. I suspe

Exactly. Data is necessary to make control flow decisions; the purely behavioural approach suffers infinite regress without some form of concrete data. I suspect that this problem was one of the reasons later actor languages came to include some kind of data; in the case of Erlang, messages are the data, compared structurally; in E, object identities can be compared without sending messages to the objects.