Why do Lisps have symbols? Well, it s largely an artifact of the fact that Lisps embed their own syntax as a data type of the language. Compilers and interpreters use symbols to represent identifiers in a program; since Lisp allows you to represent a program s syntax as data, it provides symbols because they re part of the representation.

除此以外,它们有什么用处? 好的是:

• Lisp is commonly used to implement embedded domain-specific languages. Many of the techniques used for that come from the compiler world, so symbols are an useful tool here.
• Macros in Common Lisp usually involve dealing with symbols in more detail than this answer provides. (Though in particular, generation of unique identifiers for macro expansions requires being able to generate a symbol that s guaranteed never to be equal to any other.)
• Fixed enumeration types are better implemented as symbols than strings, because symbols can be compared by reference equality.
• There are many data structures you can construct where you can get a performance benefit from using symbols and reference equality.

From Structure and Interpretation of Computer Programs Second Edition by Harold Abelson and Gerald Jay Sussman 1996:

In order to manipulate symbols we need a new element in our language: the ability to quote a data object. Suppose we want to construct the list (a b). We can’t accomplish this with (list a b), because this expression constructs a list of the values of a and b rather than the symbols themselves. This issue is well known in the context of natural languages, where words and sentences may be regarded either as semantic entities or as character strings (syntactic entities). The common practice in natural languages is to use quotation marks to indicate that a word or a sentence is to be treated literally as a string of characters. For instance, the first letter of “John” is clearly “J.” If we tell somebody “say your name aloud,” we expect to hear that person’s name. However, if we tell somebody “say ‘your name’ aloud,” we expect to hear the words “your name.” Note that we are forced to nest quotation marks to describe what somebody else might say. We can follow this same practice to identify lists and symbols that are to be treated as data objects rather than as expressions to be evaluated. However, our format for quoting differs from that of natural languages in that we place a quotation mark (traditionally, the single quote symbol ’) only at the beginning of the object to be quoted. We can get away with this in Scheme syntax because we rely on blanks and parentheses to delimit objects. Thus, the meaning of the single quote character is to quote the next object. Now we can distinguish between symbols and their values:

(define a 1)

(define b 2)

(list a b)
(1 2)

(list ’a ’b)
(a b)

(list ’a b)
(a 2)