[plt-scheme] more possible planet functions

On Feb 7, 2007, at 9:31 AM, Corey Sweeney wrote:

> I have another function that i'm thinking of adding to my plant
> package, but I'm not confidant that the API is as clean as it could
> be, so I'm looking for any more comments...
>

This is a breadth-first search.  Why not call it that:

(define (breadth-first-search fn start-list)
   (define (sql-recur-on-loop list-to-do list-done-so-far)
     (if (null? list-to-do)
         list-done-so-far
         (begin
           (let ([currently-known-records (append list-done-so-far  
list-to-do)])
             (sql-recur-on-loop
              (remove
               (lambda (element) (member element currently-known- 
records))
               (apply append
                      (map
                       fn
                       list-to-do)))
              currently-known-records)))))
   (sql-recur-on-loop start-list `()))

(define (sql-recur-on sql-function start-list)
   (breadth-first-search
    (lambda (field)
      (sqli-query s (sql-function field))
      (sqli-fetchall s))
    start-list))


... Also, if you're using this on lists of more than a couple hundred  
elements, you're probably better off using a hash table.  I don't  
have a good feel for where the break-even point would be.  If you  
leave it as a list, I would definitely re-order the arguments to  
append to put the shorter one first.

also, you could do the filter before the append, to save yourself the  
trouble of appending elements that are about to disappear.  Yikes,  
you could also just look for a nice breadth-first search written by  
someone else.

Best of luck,

John Clements

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