2016 Update

Task/Sierpinski-triangle/Haskell/sierpinski-triangle-3.hs

@@ -0,0 +1,16 @@
+import Data.List (intersperse)
+
+sierpinski :: Int -> String
+sierpinski n = let
+
+    -- Top down, each row after the first is an XOR rewrite
+    rule90 n = (scanl next ['*'] [1..n-1]) where
+        next line _ = zipWith xor (" " ++ line) (line ++ " ")
+        xor l r | l == r = ' ' | otherwise = '*'
+
+    -- Bottom up, each line above the base is indented 1 more space
+    in fst (foldr spacing ("", "") (rule90 (2^n))) where
+        spacing x (s, w) =
+            (concat [w, intersperse ' ' x, "\n", s], w ++ " ")
+
+main = putStr $ sierpinski 4