[m-dev.] for review: add `do_while/4' to std_util.m

[Tyson Dowd]

On 19-Oct-1999, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> Estimated hours taken: 2
> 
> library/std_util.m:
> 	Implement `do_while/4'.
> 
> samples/README:
> samples/all_solutions.m:
> samples/committed_choice.m:
> samples/solutions/all_solutions.m:
> samples/solutions/one_solution.m:
> samples/solutions/some_solutions.m:
> 	Move the all_solutions.m and committed_choice.m samples
> 	into a new subdirectory `solutions', renaming committed_choice.m
> 	as `one_solution.m', and add a new file `some_solutions.m'
> 	illustrating the use of `do_while/4'.
> 	(Also fix some documentation rot in samples/README.)
> 
> NEWS:
> 	Mention the new predicate std_util__do_while/4.
> 

Just one comment.

> @@ -182,6 +182,37 @@
>  :- mode unsorted_aggregate(pred(muo) is nondet, pred(mdi, di, uo) is det,
>  		di, uo) is cc_multi.
>  
> +	% This is a generalization of unsorted_aggregate which allows the
> +	% iteration to stop before all solutions have been found.
> +	% Declaratively, the specification is as follows:
> +	%
> +	%	do_while(Generator, Filter) -->
> +	%		{ solutions(Generator, Solutions) },
> +	%		do_while_2(Solutions, Filter).
> +	%
> +	%	do_while_2([], _) --> [].
> +	%	do_while_2([X|Xs], Filter) :-
> +	%		Filter(X, More),
> +	%		(if { More = yes } then
> +	%			do_while_2(Xs, Filter)
> +	%		else
> +	%			{ true }
> +	%		).

I was about to write complaining that I don't think declarative
semantics should be defined using DCG notation (because it looks a
little sloppy and confusing) but then I realized that
you have a bug in your specification anyway because of the use of :-
instead of -->.

So I think at least fix the bug, and maybe remove the DCG notation.

Apart from that the change is fine.

-- 
       Tyson Dowd           # 
                            #  Surreal humour isn't eveyone's cup of fur.
     trd at cs.mu.oz.au        # 
http://www.cs.mu.oz.au/~trd #
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