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ifix bad performance in backtracking nth and th0.

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git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1336 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
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vsc
2005-07-05 18:29:25 +00:00
parent bbfed93774
commit d62a9e2ffa
1 changed files with 12 additions and 24 deletions
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36
library/lists.yap
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@@ -112,7 +112,7 @@ nextto(X,Y, [_|List]) :-
% 1, that is nth(1, [H|_], H).
nth0(V, In, Element) :- var(V), !,
generate_nth0(V, In, Element).
generate_nth(0, V, In, Element).
nth0(0, [Head|_], Head) :- !.
nth0(N, [_|Tail], Elem) :-
M is N-1,
@@ -124,14 +124,8 @@ find_nth0(N, [_|Tail], Elem) :-
find_nth0(M, Tail, Elem).
generate_nth0(0, [Head|_], Head).
generate_nth0(I, [_|List], El) :-
generate_nth0(I1, List, El),
I is I1+1.
nth(V, In, Element) :- var(V), !,
generate_nth(V, In, Element).
generate_nth(1, V, In, Element).
nth(1, [Head|_], Head) :- !.
nth(N, [_|Tail], Elem) :-
nonvar(N), !,
@@ -144,10 +138,10 @@ find_nth(N, [_|Tail], Elem) :-
find_nth(M, Tail, Elem).
generate_nth(1, [Head|_], Head).
generate_nth(I, [_|List], El) :-
generate_nth(I1, List, El),
I is I1+1.
generate_nth(I, I, [Head|_], Head).
generate_nth(I, IN, [_|List], El) :-
I1 is I+1,
generate_nth(I1, IN, List, El).
@@ -160,7 +154,7 @@ generate_nth(I, [_|List], El) :-
% can be used to insert Elem after the Nth element of Rest.
nth0(V, In, Element, Tail) :- var(V), !,
generate_nth0(V, In, Element, Tail).
generate_nth(0, V, In, Element, Tail).
nth0(0, [Head|Tail], Head, Tail) :- !.
nth0(N, [Head|Tail], Elem, [Head|Rest]) :-
M is N-1,
@@ -172,14 +166,9 @@ find_nth0(N, [Head|Tail], Elem, [Head|Rest]) :-
find_nth0(M, Tail, Elem, Rest).
generate_nth0(0, [Head|Rest], Head, Rest).
generate_nth0(I, [Head|List], El, [Head|Rest]) :-
generate_nth0(I1, List, El, Rest),
I is I1+1.
nth(V, In, Element, Tail) :- var(V), !,
generate_nth(V, In, Element, Tail).
generate_nth(1, V, In, Element, Tail).
nth(1, [Head|Tail], Head, Tail) :- !.
nth(N, [Head|Tail], Elem, [Head|Rest]) :-
M is N-1,
@@ -191,11 +180,10 @@ find_nth(N, [Head|Tail], Elem, [Head|Rest]) :-
find_nth(M, Tail, Elem, Rest).
generate_nth(1, [Head|Rest], Head, Rest).
generate_nth(I, [Head|List], El, [Head|Rest]) :-
generate_nth(I1, List, El, Rest),
I is I1+1.
generate_nth(I, I, [Head|Tail], Head, Tail).
generate_nth(I, IN, [_|List], El, Tail) :-
I1 is I+1,
generate_nth(I1, IN, List, El, Tail).