equal? -- r7rs Definition

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Kind

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comparator;

Extended by

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• equivalent-by-value-strict-recursive? (from vonuvoli);

Procedure signature

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Procedure variants:

• ((any any) -> (boolean))
  • inputs:
    • a value of type any;
    • a value of type any;
  • output: a value of type boolean;

Exports

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• scheme:base -- (scheme base);

Exports recursive

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• scheme -- (scheme);

Description

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(equal? obj_1 obj_2)

The equal? procedure, when applied to pairs, vectors, strings and bytevectors, recursively compares them, returning #t when the unfoldings of its arguments into (possibly infinite) trees are equal (in the sense of equal?) as ordered trees, and #f otherwise. It returns the same as eqv? when applied to booleans, symbols, numbers, characters, ports, procedures, and the empty list. If two objects are eqv?, they must be equal? as well. In all other cases, equal? may return either #t or #f.

Note that records are equal? if their record types are the same and their correspondingly named fields are equal?.

Even if its arguments are circular data structures, equal? must always terminate.

(equal? 'a 'a)                  ===>  #t
(equal? '(a) '(a))              ===>  #t
(equal? '(a (b) c)
        '(a (b) c))             ===>  #t
(equal? "abc" "abc")            ===>  #t
(equal? 2 2)                    ===>  #t
(equal? (make-vector 5 'a)
        (make-vector 5 'a))     ===>  #t
(equal? '#1=(a b . #1#)
        '#2=(a b a b . #2#))    ===>  #t
(equal? (lambda (x) x)
        (lambda (y) y))         ===>  #unspecified

Note: A rule of thumb is that objects are generally equal? if they print the same.

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The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.

Referenced-types

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• any;
• boolean;