Purescala BNF (WIP)

program	object id { definition * }
	classdef
definition	classdef
	fundef
classdef	abstract class id [ { fundef * } ]?
	case class id ( args ) [ extends id ]?
	case object id [ extends id ]?
fundef	def id ( decls ) : type = { [ require( expr ) ]? expr } [ ensuring( id => * expr ) ]?