Visit for all nodes in the AST The visitor can call "next()" to continue traversal of child nodes.

Branch Nodes have this struct embedded, as these fields can be used to pass evaluation results from children.

Directional Matches: * anything that has further sub commands or accepts fancy data * no direction * several dedicated Match structs for different data types and sub commands.

The overall structure of this grammar.

Regular Matches: * anything that has further sub commands or accepts fancy data * no direction * several dedicated Match structs for different data types and sub commands.

Node is an interface implemented by all AST nodes.

Basic data type nodes which are mostly just aliases.

FIXME: pseudo "negative" Number used by the printer visitor only, for emitting a "-" between children.