permutation.logic

国外的一套开源CRM

/*
Demonstration of creating permutations.
Usage: permutation(InList, OutList)
OutList is a permutation of InList.

Try the query:
    permutation(["get kids", "mail package", "buy milk"], toDo)
which should produce the result:
    toDo = [get kids, mail package, buy milk]
    toDo = [get kids, buy milk, mail package]
    toDo = [mail package, get kids, buy milk]
    toDo = [mail package, buy milk, get kids]
    toDo = [buy milk, get kids, mail package]
    toDo = [buy milk, mail package, get kids]
    no more results
*/
select(X, [X | Rest], Rest);
select(X, [Y | Rest1], [Y | Rest2]) :- select(X, Rest1, Rest2);
permutation(InList, [H | OutRest]) :- 
    select(H, InList, InOther), 
    permutation(InOther, OutRest);
permutation([], []);