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From: an...@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.lang.forth
Subject: Re: Recursion
Date: Fri, 06 Apr 2012 14:47:32 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Andrew Haley <andre...@littlepinkcloud.invalid> writes:
>Paul Rubin <no.em...@nospam.invalid> wrote:
>> This relates to Euler problem 303.  Enumerate in increasing order, the
>> numbers that can be written in base 10 using just the digits 0, 1, and 2.
>> 
>>  : r ( n -- n ) 3 /mod dup if recurse 10 * + else drop then ;
>>  : test ( -- ) 50 0 do i r . loop ;
>
>Surely for a recursion exaple to be meaningful it has to be something
>that actually requires backtracking, such as a tree walk.  This
>example is better done with a loop:
>
>: test   3 base !  50 0 do i . loop ;

If you want just the printout, that's a solution, but in Euler303 you
want to do something else with the numbers; note the "in base 10" in
the partial problem statement above.

I used BASE, <# #s #> and >number to do this part, but my code is not
smaller (and probably slower), so one can argue that recursion is used
productively here.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
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