Re: More extensive (variable) style checking

>    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. 


I find spurious information to be deleterious to development; I want to see no 

output if something proceeds as expected.  This way it's easy to spot 

anything unusual.

In this case, I like the plan, but suppose

world :-
    writeln('Oh, bother!'),
    throw('We don't know what went wrong, but it's not good.').

Then warning about X being a singleton is false.  Likewise if the later disjunct fails.