[stack] Re: Programming Puzzle

--- In [email protected], "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



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