Parse nested generic type expressions

A message type is written like a generic type: a name, optionally followed by angle brackets holding one or more comma-separated child types, nested to any depth, for example Map<String, List<Pose>>, with spaces allowed between tokens. Parse such a string into a tree and print it back in a canonical form such as Map(String,List(Pose)), keeping the children in order. Write it as a recursive-descent parser and say how you would report malformed input.