Re: searching for closest previous element

[stephenng@xxxxxxxxxxxx]

Norm writes:
>>(define (node-list-last nl)
>>(node-list-ref nl
>>(- (node-list-length nl) 1)))

I saw node-list-ref in the spec, but it claims that it "could be 
defined" as and gives a definition that basically walks down the 
list.  I guess "could be defined" isn't the same as "is defined"; 
maybe node-list-ref is actually fast.  I'll try re-writing my code 
and see if it works better.

>From the spec:

(node-list-ref nl k)

Returns a node-list containing the kth member of nl (zero-based), if
there is such a member, and otherwise returns the empty node-list.
This could be defined as follows:
(define (node-list-ref nl i) 
(cond
    ((< i 0) 
       (empty-node-list))
     ((zero? i)
       (node-list-first nl)) 
     (else
         (node-list-ref (node-list-rest nl) (- i 1)))))


--Steve


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