hash-by-identity

example.scm

(use srfi-69)
(define h (make-hash-table eq? hash-by-identity))
(define a (cons 'a 'b))
(define b (cons 'a 'b))

(hash-table-set! h a 10)
(hahs-table-set! h b 20)

(hash-table-ref h a)
; ==> 10

(hash-table-ref h b)
; ==> 20

(hash-table-ref h (cons 'a 'b))
; ==> error!