Add password example

examples/basics/password.pl

@@ -0,0 +1,19 @@
+login :-
+    getdata(_, _),
+    writeln('Welcome!').
+login :-
+    repeat,
+    writeln('Sorry, you are not permitted.'),
+    getdata(_, _),
+    writeln('Welcome').
+
+getdata(Name, Password) :-
+    write('Username: '),
+    read(Name),
+    write('Password: '),
+    read(Password),
+    user(Name, Password).
+
+user(john, john1).
+user(jimmy, jimmy1).
+user(mary, mary1).

examples/basics/repeat.pl

@@ -0,0 +1,2 @@
+repeat.
+repeat :- repeat.