Re: More extensive (variable) style checking

Dear Jan, all,

These all seem very welcome changes and infrastructure.
Just a couple of points:

On Fri, 2 Aug 2013 17:41:02 +0200
Jan Wielemaker <[email protected]> wrote:

> The next one is less clear. A user complained to often initialise
> variables in one branch, forgetting to do so in another one. The check
> verifies that variables introduced in a disjunction and used after it
> are introduced in both branches. Thus,
> 
> 	t :-
> 	    (   hello(X)
> 	    ;   world
> 	    ),
> 	    writeln(X).
> 
> is considered something to warn about. This gives some warnings on the
> SWI-Prolog libraries. Most of them concern indeed ugly code, but not
> errornous. The question is whether this a meaningful warning? And, if

	it probably ought to be controlled by a flag. 
	the default value is debatable. probably false as to not alert inexperienced users?
   
> so, how one can avoid the warning after validating that the code is
> correct? One option for the latter is
> 
> 	t :-
> 	    (   hello(X)
> 	    ;   world,
> 		X=_
> 	    ),
> 	    writeln(X).
> 
> Now, only the compiler will complain that X=_ is pointless, which in
> itself is good because it will replace it with the VM instruction TRUE.
> The open question is how to silence this though ...
> 
	wouldn't a solution be to have a special predicate that does 
	nothing but saying that X is safe to be left out of the branch ?
		{non_}singleton(X)
		var_safe(X)
		true(X)
 
       It Is not ideal, but better than X=_ I think.

	(as mentioned elsewhere in this thread)
	How would your above example/system deal with the following ?

	p(Opts,X) :-
		( memberchk(X,Opts) -> true; X = default ).


Regards,


Nicos Angelopoulos
---
http://bioinformatics.nki.nl/~n.angelopoulos