equalp

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ANSI Common Lisp 5 Data and Control Flow 5.3 Dictionary of Data and Control Flow

5.3.36 equalp Function

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.

Summary and priorities of behavior of

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

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

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.

Allegro CL Implementation Details:

None.

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