Reducers in newlisp?

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jopython
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Joined: Tue Sep 14, 2010 3:08 pm

Reducers in newlisp?

Post by jopython »

Is it possible to have to have reducers in newlisp too as mentioned in this http://adambard.com/blog/Reducers-expla ... gh-Python/ ?

The key takeaway from the article is
This is the idea behind reducers. If you take your mapping function (map, filter, flatten, etc.), and have it modify the reducing function, you can perform any number and combination of mappings without having to repeatedly iterate through the list.

TedWalther
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Re: Reducers in newlisp?

Post by TedWalther »

Thanks, that is a very cool URL.

I sure could have used Reducers when I implemented the (combinations) function.

To make it efficient, I had to switch from map to dolist to avoid that exact problem that the Reducer functions address.

http://www.newlisp.org/index.cgi?page=Code_Snippets

Code: Select all

   (define (combinations n k (r '()))
     (if (= (length r) n)
       (list (sort r <))
       (apply append (map 
                (fn (x) (combinations n ((+ 1 $idx) k) (cons x r))) k))))

 ; (combinations 2 '(a b c))
 ; =>  ((a b) (a c) (b c))
I'd really like to know how that would look using Reducers instead of dolist. dolist did do the job very efficiently, map blew up my computer.
Cavemen in bearskins invaded the ivory towers of Artificial Intelligence. Nine months later, they left with a baby named newLISP. The women of the ivory towers wept and wailed. "Abomination!" they cried.

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