======= AST Display =========================
Package
  ClassDeclList [1]
  . ClassDecl
  .   "id" classname
  .   FieldDeclList [0]
  .   MethodDeclList [1]
  .   . (private) MethodDecl
  .   .   INT BaseType
  .   .   "f" methodname
  .   .   ParameterDeclList [2]
  .   .   . ParameterDecl
  .   .   .   INT BaseType
  .   .   .   "x"parametername 
  .   .   . ParameterDecl
  .   .   .   BOOLEAN BaseType
  .   .   .   "b"parametername 
  .   .   StmtList [0]
  .   .   LiteralExpr
  .   .     "3" IntLiteral
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