25 lines
663 B
Haskell
25 lines
663 B
Haskell
import Data.List (intersperse)
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-- Top down, each row after the first is an XOR / Rule90 rewrite.
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-- Bottom up, each line above the base is indented 1 more space.
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sierpinski :: Int -> String
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sierpinski = fst . foldr spacing ([], []) . rule90 . (2 ^)
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where
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rule90 = scanl next "*" . enumFromTo 1 . subtract 1
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where
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next =
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const
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. ( (zipWith xor . (' ' :))
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<*> (<> " ")
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)
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xor l r
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| l == r = ' '
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| otherwise = '*'
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spacing x (s, w) =
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( concat
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[w, intersperse ' ' x, "\n", s],
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w <> " "
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)
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main :: IO ()
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main = putStr $ sierpinski 4
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