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Re: Scheme is too complicated

On Fri, 30 Oct 1998, Maciej Stachowiak wrote:

> (define (hash->keys mytab)
>   (let ((real-tab (cdr mytab))
> 	(entry->key cadr)
> 	(end (vector-length real-tab)))
>     (let loop-over-tab ((index 0)
> 			  (accum ()))
>       (if (= index end)
> 	  accum
> 	  (loop-over-tab (+ index 1)
> 			 (let loop-over-bucket ((l (vector-ref real-tab index))
> 						(accum accum))
> 			   (if (null? l)
> 			       accum
> 			       (loop-over-bucket (cdr l)
> 						 (cons (car l) accum)))))))))

hrmm.  functional, pretty, and sleek.  But I bet this guy is faster:

> (define (hash->keys mytab)
>   (let ((real-tab (cdr mytab))
> 	(entry->key cadr)
> 	(end (vector-length real-tab)))
>     (do ((index 0 (+ 1 index))
> 	   (accum () (do ((l (vector-ref real-tab index) (cdr l))
> 			  (accum accum (cons (car l) accum)))
> 		         ((null? l))
> 		       accum)))
> 	  ((= index end))
>       accum)))

functional, pretty, sleek, and fast.

> ... rewriting working simple-minded code to functional but efficient
> code is not hard even by hand, and smart compilers do exist. 

I guess it takes practice  ;)

	Jay
	jglascoe@jay.giss.nasa.gov