Prolog permutation extracting solutions

permutation([], []).
permutation(L, [X|Xs]) :- select(X, L, Rest), permutation(Rest, Xs).

If I type permutation([1,2,3],R), the first solution is "[1,2,3]" but how to get to the second one without using ";" or "fail". I need to use the 2nd solution like "开发者_开发问答[1,3,2]" or so in order compare it to another list.

What I mean is:

permutation([], []).
permutation(L, [X|Xs]) :- select(X, L, Rest), permutation(Rest, Xs).

go_perm(L,P) :-     
        L = P,
        write(P),nl.

go_perm(L,P) :- 
        permutation(P,P2), % in this case i wanna get the next solution -.- 
        go_perm(L,P2).

If L = P then it finishes. Permutation of the first solution for "[1,2,3]" is "[1,2,3]". But that pulls me into stackoverflow because it runs into never-endless thing. Perhaps you understand me. Thanks!

Assuming you want to loop over the solutions to print them

One standard way to accomplish this is to fail and backtrack, as in:

print_all_permutations(X)
  :- permutation(X, Y), print(Y), nl, fail ; true.

Assuming you just want to check if a given solution is correct

You are already done. Just call the function with the reference list and the list you want to test:

permutation([1, 2, 3], [2, 1, 3]).

will return true, because [2, 1, 3] is a permutation of [1, 2, 3]. If the second argument is not a permutation, the goal will evaluate to false.

This is the magic of prolog: finding a solution, or checking if a given solution is correct, are the same thing.

In between: partial solution

The same reasoning still applies:

permutation([1, 2, 3], [2, X, 3]).

will display the only possible value for X.

Or, if you want the whole list to be the result:

X = [2, X, 3], permutation([1, 2, 3], X).

You need to look at various aggregate predicates. Here, findall would work nicely. you can invoke it:

ListIn=[1,2,3], findall(Perm, permutation(ListIn, Perm), Permutations).

This will call permutation on ListIn until it fails. Each Perm returned by permutation will be collected into the Permutations variable.

permutation is a predicate that succeeds when one list is a permutation of the other. You don't actually need to enumerate them; just write permutation([1, 2, 3], [2, 1, 3]) and Prolog will tell you "true".