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Loop without Loops
Posted: Wed Apr 20, 2011 6:29 pm
by newdep
I was wondering how many functions inside newlisp are useable to a create a functional loop with.
So.. thats without the use of 'until 'while 'for (the existing repeat/loop functions)..etc..
Here a very basic example
functions themselfs can loop i.e. running either of these will return the looped function of (print y).
Code: Select all
(define (loop x) (or (zero? x) (go x)) )
(define (go y) (print y) (loop (dec y)))
(go 10)
or
(loop 10)
Now im wondering what's more to use? I would love to see a 'map or 'apply functional loop without
the use of the pre-defined loop/repeat functions in it.
...did not figure it out yet ;-) Anyone ?
Re: Loop without Loops
Posted: Wed Apr 20, 2011 7:57 pm
by Kazimir Majorinc
Code: Select all
(eval (setf code '(when (< counter 40)
(inc counter)
(println counter)
(eval code))))
or even better, "crawler-tractor"
Code: Select all
(set 'f (lambda()
(if (< counter2 50)
(begin (println "Hi for the " (inc counter2) ". time. ")
(push (last f) f -1)
(if (> (length f) 3) (pop f 1))))))
(f)
This last is particularly charmy because it doesn't use recursion and Lutz actually made some change so it doesn't result in stack overflow at all.
I tried to do same with map,
Code: Select all
(setf L '(1 2))
(map (lambda(x)(when (< x 10)
(push (+ x 2) L -1))
(println L))
L)
but it doesn't work, i.e. original version of L is used, not modified version, perhaps some optimization. I guess that other functions are optimized on the same way. One can always use (sequence 1 50), but it looks too trivial, I think.
Finally, Lutz implemented Y-combinator from lambda-calculus in Newlisp:
http://www.newlisp.org/index.cgi?Y_Function
Re: Loop without Loops
Posted: Wed Apr 20, 2011 9:04 pm
by newdep
ahaaaaa...I thought you like this topic and i was almost certain you had your mind set to it already...Yes i remembered your crawer-tractor... realy nice ! I was close in finalizing them almost..almost near these examples you just post here, but i could not get my mind to finish it ..1 level too deep..;-) These are actualy very nice brain crackers! Well done.. love them... I missed out on the Y-combinator Ill study that Thanks!....
Re: Loop without Loops
Posted: Thu Apr 21, 2011 7:18 am
by newdep
Mind set to the right frequency and it flows again...
..more on map..
Code: Select all
# loops y * 1-second
(define (loop y)
(map (fn(x) (sleep (mul x 1000)) (println (++ y)) ) (dup 1 y)) )
#loops backwards from y to z
(setf loop (lambda(y z)
(map (fn(x) (println (dup "@" x) )) (sequence y z))
true ))
#loops backwards to 1
(setf loop (lambda(y)
(map (fn(x) (println (dup "@" x) )) (sequence y 1))
true ))
> (loop 10)
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true
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