1		:- module(pltables_export_tools, [
2		merge_attributes/3
3		]).
4
5		:- use_module(probsrc(self_check)).
6		:- use_module(probsrc(module_information)).
7
8		:- module_info(group,pltables).
9		:- module_info(description,'Tools used by several of the export modules').
10
11		% ----
12		% internal: merging of attribute lists
13		% first list: low priority, merge in
14		% second list: high priority, keep
15		% third list: Result
16		% ----
17		:-assert_must_succeed(pltables_export_tools:merge_attributes([],[],[])).
18		:-assert_must_succeed(pltables_export_tools:merge_attributes([],[attr(x)],[attr(x)])).
19		:-assert_must_succeed(pltables_export_tools:merge_attributes([attr(x)],[attr2(y)],[attr(x),attr2(y)])).
20		:-assert_must_succeed(pltables_export_tools:merge_attributes([attr(y)],[attr(x)],[attr(x)])).
21		merge_attributes([], Res, Res).
22		merge_attributes([Attr | Attrs], HiPri, Res) :-
23		functor(Attr, AttrName, Arity),
24		functor(EmptyAttr, AttrName, Arity),
25		merge_attributes(Attrs, HiPri, Res1),
26		(member(EmptyAttr, HiPri) -> Res = Res1 ; Res = [Attr | Res1]).