def each(io)
      if block_given?
        filter = BELParser::ASTFilter.new(
          BELParser::ASTGenerator.new(io),
          *TYPES)
        filter.each do |results|
          yield results
        end
      else
        enum_for(:each, io)
      end
    end
def each(io)
      if block_given?
        filter = BELParser::ASTFilter.new(
          BELParser::ASTGenerator.new(io),
          *TYPES)
        filter.each do |results|
          yield results
        end
      else
        enum_for(:each, io)
      end
    end
Yields Term AST to the block argument or provides an enumerator of
 Term AST.