CLHS: Function EQUALP

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Function EQUALP

Syntax:

equalp x y => generalized-boolean

Arguments and Values:

x---an object.

y---an object.

generalized-boolean---a generalized boolean.

Description:

Returns true if x and y are equal, or if they have components that are of the same type as each other and if those components are equalp; specifically, equalp returns true in the following cases:

Characters

  If two characters are char-equal.

Numbers

  If two numbers are the same under =.

Conses

  If the two cars in the conses are equalp and the two cdrs in the conses are equalp.

Arrays

  If two arrays have the same number of dimensions, the dimensions match, and the corresponding active elements are equalp. The types for which the arrays are specialized need not match; for example, a string and a general array that happens to contain the same characters are equalp. Because equalp performs element-by-element comparisons of strings and ignores the case of characters, case distinctions are ignored when equalp compares strings.

Structures

  If two structures S1 and S2 have the same class and the value of each slot in S1 is the same under equalp as the value of the corresponding slot in S2.

Hash Tables

  equalp descends hash-tables by first comparing the count of entries and the `:test` function; if those are the same, it compares the keys of the tables using the `:test` function and then the values of the matching keys using equalp recursively.

equalp does not descend any objects other than the ones explicitly specified above. The next figure summarizes the information given in the previous list. In addition, the figure specifies the priority of the behavior of equalp, with upper entries taking priority over lower ones.

    Type          Behavior
    number        uses =
    character     uses char-equal
    cons          descends
    bit vector    descends
    string        descends
    pathname      same as equal
    structure     descends, as described above
    Other array   descends
    hash table    descends, as described above
    Other object  uses eq

Figure 5-13. Summary and priorities of behavior of equalp

Examples:

     (equalp 'a 'b) =>  false
     (equalp 'a 'a) =>  true
     (equalp 3 3) =>  true
     (equalp 3 3.0) =>  true
     (equalp 3.0 3.0) =>  true
     (equalp #c(3 -4) #c(3 -4)) =>  true
     (equalp #c(3 -4.0) #c(3 -4)) =>  true
     (equalp (cons 'a 'b) (cons 'a 'c)) =>  false
     (equalp (cons 'a 'b) (cons 'a 'b)) =>  true
     (equalp #\A #\A) =>  true
     (equalp #\A #\a) =>  true
     (equalp "Foo" "Foo") =>  true
     (equalp "Foo" (copy-seq "Foo")) =>  true
     (equalp "FOO" "foo") =>  true

     (setq array1 (make-array 6 :element-type 'integer
                                :initial-contents '(1 1 1 3 5 7)))
    =>  #(1 1 1 3 5 7)
     (setq array2 (make-array 8 :element-type 'integer
                                :initial-contents '(1 1 1 3 5 7 2 6)
                                :fill-pointer 6))
    =>  #(1 1 1 3 5 7)
     (equalp array1 array2) =>  true
     (setq vector1 (vector 1 1 1 3 5 7)) =>  #(1 1 1 3 5 7)
     (equalp array1 vector1) =>  true

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

eq, eql, equal, =, string=, string-equal, char=, char-equal

Notes:

Object equality is not a concept for which there is a uniquely determined correct algorithm. The appropriateness of an equality predicate can be judged only in the context of the needs of some particular program. Although these functions take any type of argument and their names sound very generic, equal and equalp are not appropriate for every application.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- EQUAL-STRUCTURE:MAYBE-STATUS-QUO

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