LOGO-L> Re: Xmas - The Gift of Life - Conway's +...

[bh@anarres.CS.Berkeley.EDU (Brian Harvey)]

Bob Gorman <bgorman@kncell.org> writes:
>to b.sum :a :b
>if :debug [show (LIST ">b.sum :a :b)]
>output b.add :a :b 0
>if :debug [show (LIST "<b.sum :a :b)]
>end
>
>I made the same modification to each routine, with the same result, entrance
>works, but exit doesn't.

OUTPUT in Logo terminates the procedure it's in.  Once the procedure
has output a result, it's finished!  Try this:

to b.sum :a :b
if :debug [show (LIST ">b.sum :a :b)]
localmake "result b.add :a :b 0
if :debug [show (LIST "<b.sum :a :b "==> :result)]
output :result
end

(If you're not using UCBLogo or MSWLogo, just say MAKE instead of
LOCALMAKE.)

Footnote: The cost of this is that the call to b.add is no longer
a tail call, so more space is needed for temporary storage of local
variables.  But if you don't run out of memory, that's unimportant.

Footnote 2:  If you *are* using UCBLogo or MSWLogo, then instead of
all this effort you can just say

        trace "b.sum

and Logo will print these messages on its own.
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