The writer adapter class
Individual switch class. Not important to the user.
Defined within Switch are several Switch-derived classes: NoArgument, RequiredArgument, etc.
Raises when there is an argument for a switch which takes no argument.
Raises when a switch with mandatory argument has no argument.
Raises when the given argument does not match required format.
Raises when the given argument word can’t be completed uniquely.
LALR item. A set of rule and its lookahead tokens.