Add backtracking to the evaluator. This means we have to keep track of choicepoints which is implemented the easy but wasteful way for now.

I have also added a number which is used to differentiate variables from different application of the clauses.

1 files changed, 7 insertions, 1 deletions

diff --git a/example.pl b/example.pl
index bf30ba6..64f08ab 100644
--- a/example.pl
+++ b/example.pl
@@ -25,4 +25,10 @@ curly(A) :- A = {one,two,three}.
 
 =(A,A).
 
-:- initialization(could_be_friends(bob, sam)).
\ No newline at end of file
+length([], zero).
+length([Head|Tail], suc(Length)) :-
+	length(Tail, Length).
+
+:- initialization(could_be_friends(bob, sam)).
+
+:- initialization(length([a,b,c,d], Len)).