Add zebra puzzle example

examples/zebra_puzzle.py

@@ -0,0 +1,80 @@
+# Zebra Puzzle https://en.wikipedia.org/wiki/Zebra_Puzzle
+from neuralogic.core import R, V, Template
+from neuralogic.inference import InferenceEngine
+
+color_vars = [V.Blue, V.Yellow, V.Ivory, V.Green, V.Red]
+drink_vars = [V.OrangeJuice, V.Water, V.Tea, V.Milk, V.Coffee]
+pet_vars = [V.Horse, V.Zebra, V.Fox, V.Dog, V.Snails]
+smoke_vars = [V.Kools, V.Chesterfield, V.LuckyStrike, V.OldGold, V.Parliament]
+person_vars = [V.Norwegian, V.Spaniard, V.Ukrainian, V.Japanese, V.Englishman]
+
+template = Template()
+
+# 1. There are five houses.
+template += [R.house(i) for i in range(1, 6)]
+
+# We need to add 0 and 6 house, e.g., so that we can do R.special._in(1, Left, Right), where left is 0 (non existent)
+template += R.tmp(0, 6)
+
+template += R.solve(*person_vars, V.Zebra, V.Water) <= [
+    *[R.house(var) for var in color_vars],
+    *[R.house(var) for var in drink_vars],
+    *[R.house(var) for var in pet_vars],
+    *[R.house(var) for var in smoke_vars],
+    *[R.house(var) for var in person_vars],
+    # 2. The Englishman lives in the red house.
+    R.special.eq(V.Englishman, V.Red),
+    # 3. The Spaniard owns the dog.
+    R.special.eq(V.Spaniard, V.Dog),
+    # 4. Coffee is drunk in the green house.
+    R.special.eq(V.Coffee, V.Green),
+    # 5. The Ukrainian drinks tea.
+    R.special.eq(V.Ukrainian, V.Tea),
+    # 6. The green house is immediately to the right of the ivory house.
+    R.special.next(V.Ivory, V.RightOfIvory),
+    R.special.eq(V.Green, V.RightOfIvory),
+    # 7. The Old Gold smoker owns snails.
+    R.special.eq(V.OldGold, V.Snails),
+    # 8. Kools are smoked in the yellow house.
+    R.special.eq(V.Kools, V.Yellow),
+    # 9. Milk is drunk in the middle house.
+    R.special.eq(V.Milk, 3),
+    # 10. The Norwegian lives in the first house.
+    R.special.eq(V.Norwegian, 1),
+    # 11. The man who smokes Chesterfields lives in the house next to the man with the fox.
+    R.special.next(V.Fox, V.RightToFox),
+    R.special.next(V.LeftToFox, V.Fox),
+    R.special._in(V.Chesterfield, V.LeftToFox, V.RightToFox),
+    # 12. Kools are smoked in a house next to the house where the horse is kept.
+    R.special.next(V.Horse, V.RightToHorse),
+    R.special.next(V.LeftToHorse, V.Horse),
+    R.special._in(V.Kools, V.LeftToHorse, V.RightToHorse),
+    # 13. The Lucky Strike smoker drinks orange juice.
+    R.special.eq(V.LuckyStrike, V.OrangeJuice),
+    # 14. The Japanese smokes Parliaments.
+    R.special.eq(V.Japanese, V.Parliament),
+    # 15. The Norwegian lives next to the blue house.
+    R.special.next(V.Blue, V.RightToBlue),
+    R.special.next(V.LeftToBlue, V.Blue),
+    R.special._in(V.Norwegian, V.LeftToBlue, V.RightToBlue),
+    # In one house can live only one person, house can have only one color etc.
+    R.special.alldiff(color_vars),
+    R.special.alldiff(drink_vars),
+    R.special.alldiff(pet_vars),
+    R.special.alldiff(smoke_vars),
+    R.special.alldiff(person_vars),
+]
+
+inferene_engine = InferenceEngine(template)
+
+for solution in inferene_engine.query(R.solve(*person_vars, V.Zebra, V.Water)):
+    print("Solution:", solution)
+    for person in person_vars:
+        if solution[person] == solution[V.Zebra]:
+            print(f"Zebra owner is {person}")
+        if solution[person] == solution[V.Water]:
+            print(f"Water drinker is {person}")
+
+# Solution: {'Norwegian': '1', 'Spaniard': '4', 'Ukrainian': '2', 'Japanese': '5', 'Englishman': '3', 'Zebra': '5', 'Water': '1'}
+# Water drinker is Norwegian
+# Zebra owner is Japanese