Looking for advice. I'm adding foldl1/3 and foldr1/3 meta-predicates to the Logtalk library. These can be easily defined:
foldl1(Closure, [Head| Tail], Result) :-
foldl(Closure, Head, Tail, Result).
foldr1(Closure, [Head| Tail], Result) :-
foldr1_(Tail, Head, Closure, _, Result).
foldr1_([], Result, _, Result, Result).
foldr1_([Arg2| Args], Arg1, Closure, Acc, Result) :-
foldr1_(Args, Arg2, Closure, Acc, Acc2),
call(Closure, Arg1, Acc2, Result).
With these definitions, calling the meta-predicates with an empty list simply fail. But this doesn't allow distinguish from the case where the call fails due to one of the implicit goals constructed from the closure failing.
If you envision yourself using these meta-predicates, do you find failure on empty lists an acceptable behavior or would you prefer an exception being generated in this case?