Include Paulo Moura's Logtalk OO LP system

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Logtalk/examples/metapredicates/NOTES

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.8.4
+
+Copyright (c) 1998-2001 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+To load all objects in this library consult the metapredicates.loader utility
+file.
+
+You will also need to load the library/types.loader file (note that the 
+*.loader files are Prolog files).
+
+This example shows the use of metapredicates in Logtalk. Metapredicates are 
+predicates whose head contains arguments that will be called as goals in the 
+body of the predicate definition.

Logtalk/examples/metapredicates/SCRIPT

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+=================================================================
+Logtalk - Object oriented extension to Prolog
+Release 2.8.4
+
+Copyright (c) 1998-2001 Paulo Moura.  All Rights Reserved.
+=================================================================
+
+
+% note that "user" is a pseudo-object representing the Prolog database
+% this implies that the integer comparisons are done using the standard
+% Prolog built-in predicates
+
+| ?- sort(user)::sort([3, 1, 4, 2, 9], Sorted).
+
+call: partition([1,4,2,9],3,_358,_359)
+exit: partition([1,4,2,9],3,[1,2],[4,9])
+call: sort([1,2],_740)
+call: partition([2],1,_967,_968)
+exit: partition([2],1,[],[2])
+call: sort([],_1300)
+exit: sort([],[])
+call: sort([2],_1539)
+call: partition([],2,_1765,_1766)
+exit: partition([],2,[],[])
+call: sort([],_2093)
+exit: sort([],[])
+call: sort([],_2332)
+exit: sort([],[])
+exit: sort([2],[2])
+exit: sort([1,2],[1,2])
+call: sort([4,9],_2831)
+call: partition([9],4,_3058,_3059)
+exit: partition([9],4,[],[9])
+call: sort([],_3391)
+exit: sort([],[])
+call: sort([9],_3630)
+call: partition([],9,_3856,_3857)
+exit: partition([],9,[],[])
+call: sort([],_4184)
+exit: sort([],[])
+call: sort([],_4423)
+exit: sort([],[])
+exit: sort([9],[9])
+exit: sort([4,9],[4,9])
+
+Sorted = [1,2,3,4,9] ? 
+
+yes

Logtalk/examples/metapredicates/metapredicates.loader

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+
+:- initialization(
+	logtalk_load([
+		sort1, 
+		tracer])). 

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.

Logtalk/examples/metapredicates/tracer.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,
+		authors is 'Paulo Moura',
+		date is 2000/7/24,
+		comment is 'Tracer for a goal call and exit ports.']).
+
+
+	:- public(trace/1).
+	:- metapredicate(trace(::)).
+
+	:- mode(trace(+callable), zero_or_more).
+
+	:- info(trace/1, [
+		comment is '.',
+		argnames is ['Goal']]).
+
+
+	trace(Goal) :-
+		write('call: '), writeq(Goal), nl,
+		call(Goal),
+		write('exit: '), writeq(Goal), nl.
+		
+	trace(Goal) :-
+		write('fail: '), writeq(Goal), nl,
+		fail.
+
+
+:- end_object.