Add two more keys for the MonteCarlo Lock puzzle.

docs/source/primer.rst

@@ -203,6 +203,19 @@ grandfather toy example:
     >>> run(fresh(lambda rel, p, s: grand_father(p, s) & unify([p, s], rel)))
     [['paul', 'tom'], ['jason', 'peter'], ['tom', 'brian']]
 
+Introducing guided search:
+
+.. doctest::
+
+    >>> def recuro(e):
+    ...     return fresh(lambda a, b: conde([unify(e, ['x']), succeed],
+    ...                                     [unify(e, ['b']+a), recuro(a)],
+    ...                                     [unify(e, ['a']+b), recuro(b)]))
+    ...
+    >>> run(fresh(recuro), n=5)
+    [['x'], ['b', 'x'], ['b', 'b', 'x'], ['b', 'b', 'b', 'x'], ['b', 'b', 'b', 'b', 'x']]
+
+
 
 η-inversion
 ~~~~~~~~~~~

src/mclock.py

@@ -4,7 +4,7 @@
 
 def machine(*, rules):
     def M(α, β):
-        return condi(*[[r(α, β, machine=M), succeed] for r in rules])
+        return condi(*[[r(α, β, machine=M), succeed] for r in rules], dovetail=True)
     return M
 
 def nullo(l):

src/mclock_test.py

@@ -279,10 +279,13 @@ def test_fergusson_law_chapter(self):
                                           unify([χ, ψ], out))), n=1), []) # 6
 
     def test_the_key_chapter(self):
-        self.assertEqual(run(fresh(lambda α: mcculloch___o(α, α)), n=3), 
-                         [[5, 4, 6, 4, 2, 5, 4, 6, 4, 2],
-                          [4, 5, 6, 4, 2, 4, 5, 6, 4, 2],
-                          [5, 4, 4, 4, 6, 4, 2, 5, 4, 4, 4, 6, 4, 2]]) # the keys!!!
+        with recursion_limit(100000):
+            self.assertEqual(run(fresh(lambda α: mcculloch___o(α, α)), n=5), 
+                             [[5, 4, 6, 4, 2, 5, 4, 6, 4, 2],
+                              [4, 5, 6, 4, 2, 4, 5, 6, 4, 2],
+                              [5, 4, 4, 4, 6, 4, 2, 5, 4, 4, 4, 6, 4, 2],
+                              [4, 6, 5, 4, 2, 4, 6, 5, 4, 2, 2],
+                              [5, 4, 6, 4, 4, 4, 2, 5, 4, 6, 4, 4, 4, 2]]) # the keys!!!