80 lines
2.2 KiB
Plaintext
80 lines
2.2 KiB
Plaintext
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% example adopted from:
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% Programming Language Prolog Part 2, Modules
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% Committee Draft - January 14, 1998 X3J17/97/5
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:- object(tracer).
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:- info([
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version is 2.0,
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author is 'Paulo Moura',
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date is 2000/7/24,
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comment is 'Tracer for a goal call, exit, and fail ports.']).
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:- public(trace/1).
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:- metapredicate(trace(::)). % changes interpretation of meta-calls on trace/1 clauses
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:- mode(trace(+callable), zero_or_more).
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:- info(trace/1, [
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comment is 'Traces goal execution.',
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argnames is ['Goal']]).
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trace(Goal) :-
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write('call: '), writeq(Goal), nl,
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call(Goal), % Goal is called in the context of the object sending the message trace/1
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write('exit: '), writeq(Goal), nl.
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trace(Goal) :-
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write('fail: '), writeq(Goal), nl,
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fail.
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:- end_object.
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% sort code adopted from an example on 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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author is 'Paulo Moura',
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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, [append/3]). % calls to append(...) will be translated to list::append(...)
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:- uses(tracer, [trace/1]). % calls to trace(...) will be translated to tracer::trace(...)
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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 (quicksort algorithm).',
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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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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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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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