Re: [stack] Re: Programming Puzzle

Very nice!

I particularly like the use of intelligible names, something I too often
fail to do.
Unless, I am mistaken I believe "dup i" or "recurse" is the classical Y
combinator.
Notice the second occurence of "dup i" hidden in the definition of
"make-recursive",
which makes sense given the name. ;-)

I am going to have to throw some harder puzzles at this gang ;-)

- Christopher


On 5/16/07, Ivan Tomac <[email protected]> wrote:
>
>   --- In [email protected] <concatenative%40yahoogroups.com>,
> "Christopher Diggins"
> <cdiggins@...> wrote:
> > Define a while loop that takes a loop body and termination predicate
> > in Joy using only the following combinators:
> >
> > "ifte","cat","swap","dup","pop","i","dip" and "unit"
> >
>
> LIBRA
>
> (* Joy doesn't appear to have unit and cat combinators - unit == [] cons
> ? *)
>
> unit == [] cons ;
> cat == concat ;
>
> (* first thing's first - define cons *)
>
> cons == [unit] dip cat ;
>
> make-recursive == [dip dup i] cons ;
> fix-predicate == [dip swap ] cons ;
>
> construct-loop == [[pop] ifte] cons cons ;
>
> recurse == dup i ;
>
> while == [fix-predicate] dip make-recursive construct-loop recurse .
>
> 10 [0 >] [dup put 1 -] while .
>
> > Cheers,
> > Christopher
> >
>
> Ivan
>
> [Non-text portions of this message have been removed]
>
> 
>


[Non-text portions of this message have been removed]