======= AST Display =========================
Package
  ClassDeclList [1]
  . ClassDecl
  .   "A" classname
  .   FieldDeclList [0]
  .   MethodDeclList [1]
  .   . (public) MethodDecl
  .   .   INT BaseType
  .   .   "f" methodname
  .   .   ParameterDeclList [0]
  .   .   StmtList [1]
  .   .   . VarDeclStmt
  .   .   .   VarDecl
  .   .   .     BOOLEAN BaseType
  .   .   .     "x" varname
  .   .   .   BinaryExpr
  .   .   .     "&&" Operator
  .   .   .       BinaryExpr
  .   .   .         "<" Operator
  .   .   .           LiteralExpr
  .   .   .             "2" IntLiteral
  .   .   .           LiteralExpr
  .   .   .             "1" IntLiteral
  .   .   .       BinaryExpr
  .   .   .         ">=" Operator
  .   .   .           LiteralExpr
  .   .   .             "3" IntLiteral
  .   .   .           LiteralExpr
  .   .   .             "4" IntLiteral
=============================================