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-- constraint solving (simple generate and test) in Curry:
-- graph coloring
-- negation of =:=
diff :: a -> a -> Success
diff x y = (x == y) =:= False
{-
This is our actual map:
------------------
| | |
| | L2 |
| | |
| L1 |--------|
| | |
| | L3 |
| | |
------------------
-}
data Color = Red | Green | Yellow
isColor :: Color -> Success
isColor Red = success
isColor Green = success
isColor Yellow = success
-- possible colorings:
coloring :: Color -> Color -> Color -> Success
coloring l1 l2 l3 = isColor l1 & isColor l2 & isColor l3
-- correct coloring:
correct :: Color -> Color -> Color -> Success
correct l1 l2 l3 = diff l1 l2 & diff l1 l3 & diff l2 l3
-- test+generate solution:
goal :: Color -> Color -> Color -> Success
goal l1 l2 l3 = PEVAL (correct l1 l2 l3 & coloring l1 l2 l3)
main :: (Color, Color, Color)
main = goal l1 l2 l3 &> (l1, l2, l3) where l1, l2, l3 free
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