The document describes code for sending a message in a messaging system. It defines a message with a tag and recipient, adds that single message to a list of messages, and sends the list. It also describes data structures for maps that can store and retrieve values by key, and lists that can store values in a Cons cell structure with a type.

19. msg = {_tag : "main"; _recipient : _sender};
msgs = one_msg msg;
send msgs

30. Emp <key> <value>
Map[key] := <value>
Map[key1][key2] := <value>
var <- Map[key]
var <- exits Map[key]
delete Map[key]
to_list Map

32. Nil {type}
Cons {type} <newValue> <restValue>

38. Touch Bar