Re: LOGO-L> QUESTION ON CONDITIONAL OUTPUTS

[George Mills <mills@softronix.com>]

There are plenty of legitimate situations where complex
recursion can be used that will output "complex"
stack dumps and is not a demonstration of being
overkill.

Also a lot of folks generalize that recursion only exists
if the calling the procedure calls itself. I think
some of the most interesting examples of recursion are
when procedure a, calls b, calls c, which then calls a.
Heuristics would again get tricky. A good example of
this is parsing expressions.

Going slightly off topic:

Also keep in mind that you can have deep recursion
in UCBLogo/MSWLogo that is detecteed as tail recursive
which is just as therectically efficient as iterative
solutions and is just an alternive interative syntax.

Think of the common example in C where folks do
something like.

for (pointer=&things;pionter!=null;pointer=pointer.next)
  {
  do stuff with pointer
  }

And in logo

to do_stuff :things
  if emptyp :things [stop]        ; pointer != null
  do something with first :things ; do stuff
  do_stuff butfirst :things       ; pointer=pointer.next
end

Chuck Shavit wrote:
> 
> At 12:44 AM 4/26/98 -0400, George Mills wrote:
> >I think your idea of a call stack of errors is great.
> >But could get a bit messy on deeply recursive procedures.
> 
> Should be easy enough to add heuristics which will print something like
>        ADD cannot add a non numeric value.  It had inputs A and 3.
>        It was called from ADDLISTS [A 6] [9 2]
>        Which was called from ADDLISTS [4 A 6] [1 9 2]
>        ... (75 nested calls to ADDLISTS)
>        Which was called from ADDLISTS [(78 members...)] [(78 members...)]
>        Which was called from MAIN
>        Which was called from the command line.
> 
> Plus (sorry Brian, I had to add this), messy traceback on deeply recursive
> calls could demonstare the suitability of for-loop style iteration to some
> cases where recursion is an overkill.
> 
> Chuck Shavit
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