recursion - Recursive numeric equality in Scheme -


it seems scheme considers integer , floating point versions of number different when using equal?, same when using = compare them:

(equal? 2 2.0)  ; => #f (= 2 2.0)       ; => #t

however, if have recursive structure numeric parts (or simple list of numbers), there method compare them uses = numeric comparisons?

(equal? '(2 3) '(2.0 3.0))  ; => #f (= '(2 3) '(2.0 3.0))       ; error: contract violation

i can write own equality checker, this:

(define myequal?   (lambda (x y)     (cond ((and (null? x) (null? y)) #t)           ((or (null? x) (null? y)) #f)           ((and (pair? x) (pair? y))            (and (myequal? (car x) (car y))                 (myequal? (cdr x) (cdr y))))           ((or (pair? x) (pair? y)) #f)           ((and (number? x) (number? y)) (= x y))           ((or (number? x) (number? y)) #f)           (else (equal? x y)))))

but seems common enough task scheme might have builtin method this.

in racket can build notion of equality want of equal?/recur built-in procedure:

;; equalish? : any -> boolean ;; equal?, use = numbers (including within compound data) (define (equalish? b)   (if (and (number? a) (number? b))       (= b)       (equal?/recur b equalish?)))  (equalish? '(2 3) '(2.0 3.0)) ;; => #t

the equal?/recur procedure handles recurring through pairs, structures, etc.


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