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yap-6.3/Logtalk/examples/metapredicates/sort1.lgt

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% sort code adopted from an example in the SICStus Prolog User Manual
% metapredicate example taken from Prolog Part 2, Modules - Committee Draft
:- object(sort(_Type)).
:- info([
version is 1.0,
authors is 'Paulo Moura',
date is 2000/7/24,
comment is 'List sorting parameterized by the type of the list elements.']).
:- uses(list).
:- uses(tracer).
:- calls(comparingp).
:- public(sort/2).
:- mode(sort(+list, -list), one).
:- info(sort/2, [
comment is 'Sorts a list in ascending order.',
argnames is ['List', 'Sorted']]).
:- private(partition/4).
:- mode(partition(+list, +nonvar, -list, -list), one).
:- info(partition/4, [
comment is 'Partition a list in two lists containing the elements smaller and larger than a pivot.',
argnames is ['List', 'Pivot', 'Small', 'Large']]).
sort([], []).
sort([Head| Tail], Sorted) :-
tracer::(
trace(partition(Tail, Head, Small, Large)),
trace(sort(Small, Sorted1)),
trace(sort(Large, Sorted2))),
list::append(Sorted1, [Head| Sorted2], Sorted).
partition([], _, [], []).
partition([Head| Tail], Pivot, Small, Large) :-
parameter(1, Type),
( Type::(Head < Pivot) ->
Small = [Head| Small1], Large = Large1
; Small = Small1, Large = [Head| Large1]
),
partition(Tail, Pivot, Small1, Large1).
:- end_object.