This operation expects a string, to be interpreted as a ticker symbol for a stock, and returns a current quote for that stock, a float value.
该操作等待一个字符串，被解释为股票的报价机符号，然后返回当前该股票报价，一个浮点值。
Historical quote: the consumer passes in a stock symbol and a date; the provider returns a complex quote for the indicated stock and date.
历史报价：使用者传入股票代码和日期；提供程序返回指定股票和日期的复杂报价。
The result is then combined with the symbol quote into a list so that Scheme will treat it as a literal value when it becomes code.
然后，结果与符号 quote 合并到一个列表中，这样 Scheme 就会在将其转换成代码时将其作为一个文本值进行处理。
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