Re: LOGO-L> Recursion

["Olga Tuzova" <olgatu@ort.spb.ru>]

> Date:          Wed, 18 Mar 1998 23:22:47 +1000
> From:          Bill Mackay <wmackay@scu.edu.au>
> To:            logo-l@gsn.org
> Subject:       LOGO-L> Recursion
> Reply-to:      Bill Mackay <wmackay@scu.edu.au>

> Hello,
> I've just joined the list so maybe this has been covered - but I didn't
> see it in the archives.  Can someone explain when we would use tail
> recursion or embedded recursion? Perhaps an example may suffice.
> Thanks in advance,
> Bill Mackay

Bill,

I've never met here html-files with pictures being sent as an 
attachment, so I'm not sure it will work well. Nevertheless I'm 
trying.

The attachment contains html-file and two animated pictures of 
spirals to demonstrate the difference between tail and embedded 
recursion.

These pictures are just illustrating Jim Muller's MAZE and AMAZE.
You'll see, the behaviour of SPIRAL1 (spiral1a.gif) differs from one 
of SPIRAL2 (spiral2a.gif) and the behaviour of SPIRAL2 coinsides  
with the one of SPIRAL3.

TO SPIRAL1 :A
   IF :A<10 [STOP] 
   FD :A  RT 90
   SPIRAL1 :A-10
END

TO SPIRAL2 :A
   IF :A<10 [STOP] 
   SPIRAL2 :A-10
   FD :A  RT 90
END

TO SPIRAL3 :A
   IF :A>100 [STOP] 
   FD :A  RT 90
   SPIRAL3 :A+10
END

All the best,
Olga.
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   ---- File information -----------
     File:  spir_snd.htm
     Date:  19 Mar 1998, 15:14
     Size:  1349 bytes.
     Type:  HTML-text

Title: Spirals Demo

These pictures are to display the difference between embedded recursion and a tail one.
The difference in behaviour of spiral 1 and spiral 2 is obvious, though the codes look very much alike. And, though the codes are different for spiral 2 and spiral 3, their behaviour is similar.

SPIRAL1 100	SPIRAL2 100	SPIRAL3 10
TO SPIRAL1 :A IF :A<10 [STOP] FD :A RT 90 SPIRAL1 :A-10 END	TO SPIRAL2 :A IF :A<10 [STOP] SPIRAL2 :A-10 FD :A RT 90 END	TO SPIRAL3 :A IF :A>100 [STOP] FD :A RT 90 SPIRAL3 :A+10 END

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   ---- File information -----------
     File:  spiral1a.gif
     Date:  15 Feb 1998, 17:05
     Size:  6734 bytes.
     Type:  GIF-image

spiral1a.gif

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     File:  spiral2a.gif
     Date:  15 Feb 1998, 17:07
     Size:  5561 bytes.
     Type:  GIF-image

spiral2a.gif