Hi!
Repeatedly I need an equivalence predicate that performs structural
comparison but also compares numbers numerically (as `=' does, note
that `equal?' does not use `=' for number comparison). Common Lisp in
all its archaic cruftiness at least provides EQUALP which does basically
the right thing (but is case-insensitive).
Here my attempt:
; an actual implementation would be more efficient and would compare
; structured data by lower-level means:
(define (equal?? x y)
(let walk ((x x) (y y))
(cond ((eq? x y))
((pair? x)
(and (pair? y)
(walk (car x) (car y))
(walk (cdr x) (cdr y))))
((vector? x)
(and (vector? y)
(walk (vector->list x) (vector->list y))))
((string? x)
(and (string? y)
(string=? x y)))
((number? x)
(and (number? y)
(= x y)))
(else #f))))
Any ideas for a better name? Any considerations that
should be taken into account?
cheers,
felix
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