Logtalk 2.26.2 files.

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Logtalk/examples/metapredicates/metapredicates.lgt

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+
+% example adopted from:
+% Programming Language Prolog Part 2, Modules
+% Committee Draft - January 14, 1998 X3J17/97/5
+
+:- object(tracer).
+
+	:- info([
+		version is 2.0,
+		author is 'Paulo Moura',
+		date is 2000/7/24,
+		comment is 'Tracer for a goal call, exit, and fail ports.']).
+
+	:- public(trace/1).
+	:- metapredicate(trace(::)).	% changes interpretation of meta-calls on trace/1 clauses
+	:- mode(trace(+callable), zero_or_more).
+	:- info(trace/1, [
+		comment is 'Traces goal execution.',
+		argnames is ['Goal']]).
+
+	trace(Goal) :-
+		write('call: '), writeq(Goal), nl,
+		call(Goal),		% Goal is called in the context of the object sending the message trace/1
+		write('exit: '), writeq(Goal), nl.
+		
+	trace(Goal) :-
+		write('fail: '), writeq(Goal), nl,
+		fail.
+
+:- end_object.
+
+
+% sort code adopted from an example on the SICStus Prolog User Manual
+% metapredicate example taken from Prolog Part 2, Modules - Committee Draft
+
+:- object(sort(_Type)).
+
+	:- info([
+		version is 1.0,
+		author is 'Paulo Moura',
+		date is 2000/7/24,
+		comment is 'List sorting parameterized by the type of the list elements.']).
+
+	:- uses(list, [append/3]).		% calls to append(...) will be translated to list::append(...)
+	:- uses(tracer, [trace/1]).		% calls to trace(...) will be translated to tracer::trace(...)
+
+	:- calls(comparingp).
+
+	:- public(sort/2).
+	:- mode(sort(+list, -list), one).
+	:- info(sort/2, [
+		comment is 'Sorts a list in ascending order (quicksort algorithm).',
+		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) :-
+		trace(partition(Tail, Head, Small, Large)),
+		trace(sort(Small, Sorted1)),
+		trace(sort(Large, Sorted2)),
+		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.