Common Lisp 中的 eq、eql、equal 和 equalp 有什么区别? [英] What's the difference between eq, eql, equal and equalp, in Common Lisp?

问题描述

Common Lisp 中的 eq、eql、equal 和 equalp 有什么区别?我知道他们中的一些人检查类型，他们中的一些人检查类型以及所有这些，但哪个是哪个?什么时候比其他的更好用?

What's the difference between eq, eql, equal and equalp, in Common Lisp? I understand that some of them check types, some of them check across types an all that, but which is which? When is one better to use than the others?

推荐答案

来自 Common Lisp:相等谓词

(eq x y) 为真当且仅当 x 和 y 是同一个对象.

(eq x y) is true if and only if x and y are the same identical object.

eql 谓词如果其参数是 eq，或者它们是具有相同值的相同类型的数字，或者它们是表示相同的字符.

The eql predicate is true if its arguments are eq, or if they are numbers of the same type with the same value, or if they are character objects that represent the same character.

如果 equal 谓词的参数是结构相似(同构)的对象，则该谓词为真.一个粗略的经验法则是，当且仅当它们的打印表示相同时，两个对象才相等.

The equal predicate is true if its arguments are structurally similar (isomorphic) objects. A rough rule of thumb is that two objects are equal if and only if their printed representations are the same.

如果两个对象相等，则它们是equalp；如果它们是字符并且满足char-equal，则忽略字母大小写和字符的某些其他属性；如果它们是数字并且具有相同的数值，即使它们是不同的类型；或者如果它们的组件都是 equalp.

Two objects are equalp if they are equal; if they are characters and satisfy char-equal, which ignores alphabetic case and certain other attributes of characters; if they are numbers and have the same numerical value, even if they are of different types; or if they have components that are all equalp.

以下是我在上面链接到的同一页面中的一些示例:

Here are some examples from the same page I linked to above:

(eq 'a 'b) is false. 
(eq 'a 'a) is true. 
(eq 3 3) might be true or false, depending on the implementation. 
(eq 3 3.0) is false. 
(eq 3.0 3.0) might be true or false, depending on the implementation. 
(eq #c(3 -4) #c(3 -4)) 
  might be true or false, depending on the implementation. 
(eq #c(3 -4.0) #c(3 -4)) is false. 
(eq (cons 'a 'b) (cons 'a 'c)) is false. 
(eq (cons 'a 'b) (cons 'a 'b)) is false. 
(eq '(a . b) '(a . b)) might be true or false. 
(progn (setq x (cons 'a 'b)) (eq x x)) is true. 
(progn (setq x '(a . b)) (eq x x)) is true. 
(eq #A #A) might be true or false, depending on the implementation. 
(eq "Foo" "Foo") might be true or false. 
(eq "Foo" (copy-seq "Foo")) is false. 
(eq "FOO" "foo") is false.


(eql 'a 'b) is false. 
(eql 'a 'a) is true. 
(eql 3 3) is true. 
(eql 3 3.0) is false. 
(eql 3.0 3.0) is true. 
(eql #c(3 -4) #c(3 -4)) is true. 
(eql #c(3 -4.0) #c(3 -4)) is false. 
(eql (cons 'a 'b) (cons 'a 'c)) is false. 
(eql (cons 'a 'b) (cons 'a 'b)) is false. 
(eql '(a . b) '(a . b)) might be true or false. 
(progn (setq x (cons 'a 'b)) (eql x x)) is true. 
(progn (setq x '(a . b)) (eql x x)) is true. 
(eql #A #A) is true. 
(eql "Foo" "Foo") might be true or false. 
(eql "Foo" (copy-seq "Foo")) is false. 
(eql "FOO" "foo") is false.


(equal 'a 'b) is false. 
(equal 'a 'a) is true. 
(equal 3 3) is true. 
(equal 3 3.0) is false. 
(equal 3.0 3.0) is true. 
(equal #c(3 -4) #c(3 -4)) is true. 
(equal #c(3 -4.0) #c(3 -4)) is false. 
(equal (cons 'a 'b) (cons 'a 'c)) is false. 
(equal (cons 'a 'b) (cons 'a 'b)) is true. 
(equal '(a . b) '(a . b)) is true. 
(progn (setq x (cons 'a 'b)) (equal x x)) is true. 
(progn (setq x '(a . b)) (equal x x)) is true. 
(equal #A #A) is true. 
(equal "Foo" "Foo") is true. 
(equal "Foo" (copy-seq "Foo")) is true. 
(equal "FOO" "foo") is false.


(equalp 'a 'b) is false. 
(equalp 'a 'a) is true. 
(equalp 3 3) is true. 
(equalp 3 3.0) is true. 
(equalp 3.0 3.0) is true. 
(equalp #c(3 -4) #c(3 -4)) is true. 
(equalp #c(3 -4.0) #c(3 -4)) is true. 
(equalp (cons 'a 'b) (cons 'a 'c)) is false. 
(equalp (cons 'a 'b) (cons 'a 'b)) is true. 
(equalp '(a . b) '(a . b)) is true. 
(progn (setq x (cons 'a 'b)) (equalp x x)) is true. 
(progn (setq x '(a . b)) (equalp x x)) is true. 
(equalp #A #A) is true. 
(equalp "Foo" "Foo") is true. 
(equalp "Foo" (copy-seq "Foo")) is true. 
(equalp "FOO" "foo") is true.

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