Prolog Connected Edge of a graph

Question

I want to make a predicate that check if a node can reach another node in graph in prolog. e.g Connected(1,X,[[1,3],[3,4],[2,5]]) The first argument is the node I want to start the second is the node I want to reach and the third is a list of edges. So far I have managed to do it but I get an infinite loop when I try to get all the nodes I reach by using findall/3.

Is there any way to stop the infinite loop or I should thing the problem from the beggining?

Here is my code so far:

 match([X,Y],List):- member([X,Y], List).
 match([X,Y],List):- member([Y,X], List).


go(X,Y,List):-match([X,Y],List).
go(X,Y,List):-match([X,Z],List),go(Z,Y,List).

goes(X,List,List2):-findall(Y,go(X,Y,List),List2).

I am new in Prolog and I cannot figure out what I am doing wrong.

Answer 1

a possible correction to your code

match([X,Y], List, Rest):- select([X,Y], List, Rest).
match([X,Y], List, Rest):- select([Y,X], List, Rest).

go(X,Y,List) :- match([X,Y],List,_).
go(X,Y,List) :- match([X,Z],List,Rest), go(Z,Y,Rest).

goes(X,List,List2) :- findall(Y, go(X,Y,List), List2).

now match 'consumes' an edge, then avoid infinite looping

Answer 2

Have a look at what ?- gtrace, goes(1,[[1,3],[3,4],[2,5]], X). Does.

For all recursions go :- go you need a condition when it stops.

In you case I recommend to add an argument Traversed which is a list of all nodes(or edges) you have visited. Then you do not go over nodes again if you have visited them already. So you get less and less elements to recursively look at and the recorsion ends at some point.

Many recursions use the predicate !. Have a look at it.