+(define* (intmap-prev bs #:optional i)
+ (define (visit-branch node shift i)
+ (let lp ((i i) (idx (logand (ash i (- shift)) *branch-mask*)))
+ (and (<= 0 idx)
+ (or (visit-node (vector-ref node idx) shift i)
+ (lp (1- (round-down i shift)) (1- idx))))))
+ (define (visit-node node shift i)
+ (and node
+ (if (zero? shift)
+ i
+ (visit-branch node (- shift *branch-bits*) i))))
+ (match bs
+ (($ <intmap> min shift root)
+ (let* ((i (if (and i (< i (+ min (ash 1 shift))))
+ (- i min)
+ (1- (ash 1 shift)))))
+ (and (<= 0 i)
+ (let ((i (visit-node root shift i)))
+ (and i (+ min i))))))))
+
+(define (intmap-fold f map seed)
+ (define (visit-branch node shift min seed)
+ (let ((shift (- shift *branch-bits*)))
+ (if (zero? shift)
+ (let lp ((i 0) (seed seed))
+ (if (< i *branch-size*)
+ (let ((elt (vector-ref node i)))
+ (lp (1+ i)
+ (if elt
+ (f (+ i min) elt seed)
+ seed)))
+ seed))
+ (let lp ((i 0) (seed seed))
+ (if (< i *branch-size*)
+ (let ((elt (vector-ref node i)))
+ (lp (1+ i)
+ (if elt
+ (visit-branch elt shift (+ min (ash i shift)) seed)
+ seed)))
+ seed)))))
+ (match map
+ (($ <intmap> min shift root)
+ (cond
+ ((not root) seed)
+ ((zero? shift) (f min root seed))
+ (else (visit-branch root shift min seed))))))
+
+(define* (intmap-union a b #:optional (meet meet-error))