Re: [eclipse-clp-users] Increment variable

On 05/03/2013 15:39, Cédric Moonen wrote:
> Hello,
>
> First, I am sorry to post such a newbie question but I'm very new to Eclipse-clp and I've been
> reading a bit in the tutorial but couldn't find an answer to my question.
>
> So, I'm using a Java program which is actually executing a query via the OutOfProcessEclipse::rcp
> method. This is a very simple query which calls a predicate to find a solution and then output this
> solution to a file:
>
> findSolution(X), generateFile("Solution.txt", X)
>
> I need to modify this query so that not only the first solution gets generated to a file, but all
> solutions (to different files: Solution1.txt, Solution2.txt, ... ). So, I've found that I can use
> findall in this way:
>
> findall(X, findSolution(X), List), ( foreach(Inst, List) do ( sprintf(FileName,
> "Solution%d.txt",[Index]), generateFile(FileName, Inst) ) )
>
> So, I need to have the Index variable to reflect the iteration count. I tried several things (use
> foreachelem, count, ...) but I didn't succeed in finding a way to do that.

You add a 'count'-iterator to the loop:

     ...
     ( foreach(Inst, List), count(Index,1,_) do
         sprintf(FileName, "Solution%d.txt",[Index]),
         generateFile(FileName, Inst) )
     )


Having said that, using findall plus iterating through the results is
not the most efficient way to do this.  You can do it more directly,
but it needs a "failure-driven loop" and a non-logical counter ("shelf"):

solutions_to_files :-
     shelf_create(count(0), Handle),
     (
         findSolution(X),  % possibly multiple solutions

         shelf_inc(Handle, 1),
         shelf_get(Handle, 1, Index),
         sprintf(FileName, "Solution%d.txt",[Index]),
         generateFile(FileName, X),

         fail  % to find the next solution
     ;
         true  % no more solution
     ).


And finally, you should probably consider not to use files at all...


-- Joachim