September 2017 Update

Task/Repeat-a-string/Haskell/repeat-a-string-6.hs

@@ -0,0 +1,9 @@
+repString :: String -> Int -> String
+repString s n =
+  let rep x = xs
+        where
+          xs = mappend x xs
+  in take (n * length s) (rep s)
+
+main :: IO ()
+main = print $ repString "ha" 5

Task/Repeat-a-string/Haskell/repeat-a-string-7.hs

@@ -0,0 +1,25 @@
+import Data.Tuple (swap)
+import Data.List (unfoldr)
+import Control.Monad (join)
+
+-- BY RHIND PAPYRUS 'EGYPTIAN' OR 'ETHIOPIAN' MULTIPLICATION ------------------
+repString :: Int -> String -> String
+repString n s =
+  foldr
+    (\(d, x) a ->
+        if d > 0 -- Is this power of 2 needed for the binary recomposition ?
+          then mappend a x
+          else a)
+    mempty $
+  zip
+    (unfoldr
+       (\h ->
+           if h > 0
+             then Just $ swap (quotRem h 2) -- Binary decomposition of n
+             else Nothing)
+       n)
+    (iterate (join mappend) s) -- Iterative duplication ( mappend to self )
+
+-- TEST -----------------------------------------------------------------------
+main :: IO ()
+main = print $ repString 500 "ha"