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GraphLife

 

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Kevin Reid
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GraphLife

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This is a somewhat odd cellular automaton implementation in Haskell. It encodes the shape of the world, and the stepping rule, in the data structure. Briefly:

data Cell v n = Cell {
  value     :: v,
  neighbors :: n (Cell v n),
  future    :: Cell v n }

-- Build a cell and its chain of futures, given its rule, similar neighbors,
-- and initial value.
mkCell :: Functor n => (v -> n v -> v) -> v -> n (Cell v n) -> Cell v n
mkCell rule val nei = initial
  where initial = Cell val nei (calcFuture initial)
        calcFuture c = c'
          where c' = Cell (rule (value c) (fmap value (neighbors c)))
                          (fmap future (neighbors c))
                          (calcFuture c')

data Moore c = Moore c c c c c c c c

-- Conway's Life
evalLife :: Bool -> Moore Bool -> Bool
evalLife v n = f v (sumN fromEnum n)
  where f _    3 = True
        f True 2 = True
        f _    _ = False

The remainder of the code is routines for setting up worlds and displaying them.

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