2001-06-06 20:40:57 +01:00
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% sort code adopted from an example in the SICStus Prolog User Manual
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% metapredicate example taken from Prolog Part 2, Modules - Committee Draft
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:- object(sort(_Type)).
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:- info([
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version is 1.0,
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2003-02-05 00:15:28 +00:00
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author is 'Paulo Moura',
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2001-06-06 20:40:57 +01:00
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date is 2000/7/24,
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comment is 'List sorting parameterized by the type of the list elements.']).
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:- uses(list).
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:- uses(tracer).
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:- calls(comparingp).
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:- public(sort/2).
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:- mode(sort(+list, -list), one).
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:- info(sort/2, [
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comment is 'Sorts a list in ascending order.',
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argnames is ['List', 'Sorted']]).
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:- private(partition/4).
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:- mode(partition(+list, +nonvar, -list, -list), one).
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:- info(partition/4, [
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comment is 'Partition a list in two lists containing the elements smaller and larger than a pivot.',
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argnames is ['List', 'Pivot', 'Small', 'Large']]).
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sort([], []).
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sort([Head| Tail], Sorted) :-
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tracer::(
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trace(partition(Tail, Head, Small, Large)),
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trace(sort(Small, Sorted1)),
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trace(sort(Large, Sorted2))),
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list::append(Sorted1, [Head| Sorted2], Sorted).
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partition([], _, [], []).
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partition([Head| Tail], Pivot, Small, Large) :-
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parameter(1, Type),
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( Type::(Head < Pivot) ->
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Small = [Head| Small1], Large = Large1
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; Small = Small1, Large = [Head| Large1]
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),
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partition(Tail, Pivot, Small1, Large1).
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:- end_object.
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