======= AST Display =========================
Package
  ClassDeclList [1]
  . ClassDecl
  .   "Test" classname
  .   FieldDeclList [0]
  .   MethodDeclList [1]
  .   . (public) MethodDecl
  .   .   VOID BaseType
  .   .   "p" methodname
  .   .   ParameterDeclList [0]
  .   .   StmtList [1]
  .   .   . AssignStmt
  .   .   .   IdRef
  .   .   .     "a" Identifier
  .   .   .   RefExpr
  .   .   .     IdRef
  .   .   .       "b" Identifier
=============================================