| 1 | |
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| 2 | % example adapted from: |
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| 3 | % Programming Language Prolog Part 2, Modules |
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| 4 | % Committee Draft - January 14, 1998 X3J17/97/5 |
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| 5 | |
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| 6 | :- object(tracer). |
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| 7 | |
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| 8 | :- info([ |
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| 9 | version is 2.1, |
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| 10 | author is 'Paulo Moura', |
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| 11 | date is 2006/9/17, |
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| 12 | comment is 'Tracer for a goal call, exit, and fail ports.']). |
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| 13 | |
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| 14 | :- public(trace/1). |
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| 15 | :- meta_predicate(trace(::)). % changes interpretation of meta-calls on trace/1 clauses |
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| 16 | :- mode(trace(+callable), zero_or_more). |
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| 17 | :- info(trace/1, [ |
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| 18 | comment is 'Traces goal execution.', |
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| 19 | argnames is ['Goal']]). |
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| 20 | |
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| 21 | trace(Goal) :- |
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| 22 | write('call: '), writeq(Goal), nl, |
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| 23 | call(Goal), % Goal is called in the context of the object sending the message trace/1 |
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| 24 | write('exit: '), writeq(Goal), nl. |
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| 25 | |
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| 26 | trace(Goal) :- |
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| 27 | write('fail: '), writeq(Goal), nl, |
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| 28 | fail. |
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| 29 | |
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| 30 | :- end_object. |
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| 31 | |
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| 32 | |
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| 33 | % sort code adapted from an example on the SICStus Prolog User Manual |
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| 34 | % meta-predicate example taken from Prolog Part 2, Modules - Committee Draft |
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| 35 | |
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| 36 | :- object(sort(_Type)). |
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| 37 | |
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| 38 | :- info([ |
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| 39 | version is 1.0, |
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| 40 | author is 'Paulo Moura', |
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| 41 | date is 2000/7/24, |
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| 42 | comment is 'List sorting parameterized by the type of the list elements.']). |
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| 43 | |
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| 44 | :- uses(list, [append/3]). % calls to append(...) will be translated to list::append(...) |
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| 45 | :- uses(tracer, [trace/1]). % calls to trace(...) will be translated to tracer::trace(...) |
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| 46 | |
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| 47 | :- calls(comparingp). |
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| 48 | |
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| 49 | :- public(sort/2). |
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| 50 | :- mode(sort(+list, -list), one). |
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| 51 | :- info(sort/2, [ |
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| 52 | comment is 'Sorts a list in ascending order (quicksort algorithm).', |
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| 53 | argnames is ['List', 'Sorted']]). |
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| 54 | |
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| 55 | :- private(partition/4). |
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| 56 | :- mode(partition(+list, +nonvar, -list, -list), one). |
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| 57 | :- info(partition/4, [ |
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| 58 | comment is 'Partition a list in two lists containing the elements smaller and larger than a pivot.', |
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| 59 | argnames is ['List', 'Pivot', 'Small', 'Large']]). |
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| 60 | |
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| 61 | sort([], []). |
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| 62 | |
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| 63 | sort([Head| Tail], Sorted) :- |
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| 64 | trace(partition(Tail, Head, Small, Large)), |
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| 65 | trace(sort(Small, Sorted1)), |
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| 66 | trace(sort(Large, Sorted2)), |
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| 67 | append(Sorted1, [Head| Sorted2], Sorted). |
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| 68 | |
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| 69 | partition([], _, [], []). |
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| 70 | |
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| 71 | partition([Head| Tail], Pivot, Small, Large) :- |
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| 72 | parameter(1, Type), |
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| 73 | ( Type::(Head < Pivot) -> |
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| 74 | Small = [Head| Small1], Large = Large1 |
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| 75 | ; Small = Small1, Large = [Head| Large1] |
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| 76 | ), |
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| 77 | partition(Tail, Pivot, Small1, Large1). |
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| 78 | |
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| 79 | :- end_object. |
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