:- object(numberlist,
implements(numberlistp),
extends(list)).
:- info([
version is 1.0,
author is 'Paulo Moura',
date is 2000/7/24,
comment is 'List of numbers predicates.']).
average([], 0).
average([N| Ns], Average) :-
average([N| Ns], 0, 0, Average).
average([], Length, Sum, Average) :-
Average is Sum / Length.
average([N| Ns], Lacc, Sacc, Average) :-
Lacc2 is Lacc + 1,
Sacc2 is Sacc + N,
average(Ns, Lacc2, Sacc2, Average).
min([N| Ns], Min) :-
min(Ns, N, Min).
min([], Min, Min).
min([N| Ns], Aux, Min) :-
N < Aux ->
min(Ns, N, Min)
;
min(Ns, Aux, Min).
max([N| Ns], Max) :-
max(Ns, N, Max).
max([], Max, Max).
max([N| Ns], Aux, Max) :-
N > Aux ->
max(Ns, N, Max)
max(Ns, Aux, Max).
sum(List, Sum) :-
sum(List, 0, Sum).
sum([], Sum, Sum).
sum([N| Ns], Acc, Sum) :-
Acc2 is Acc + N,
sum(Ns, Acc2, Sum).
valid(List) :-
nonvar(List),
\+ \+ valid2(List).
valid2([]).
valid2([Head| Tail]) :-
number(Head),
valid2(Tail).
:- end_object.
