Data commit

Task/Look-and-say-sequence/Haskell/look-and-say-sequence.hs

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+import Control.Monad (liftM2)
+import Data.List (group)
+
+-- this function is composed out of many functions; data flows from the bottom up
+lookAndSay :: Integer -> Integer
+lookAndSay = read                                   -- convert digits to integer
+           . concatMap                              -- concatenate for each run,
+               (liftM2 (++) (show . length)         --    the length of it
+                            (take 1))               --    and an example member
+           . group                                  -- collect runs of the same digit
+           . show                                   -- convert integer to digits
+
+-- less comments
+lookAndSay2 :: Integer -> Integer
+lookAndSay2 = read . concatMap (liftM2 (++) (show . length)
+                                            (take 1))
+            . group . show
+
+
+-- same thing with more variable names
+lookAndSay3 :: Integer -> Integer
+lookAndSay3 n = read (concatMap describe (group (show n)))
+  where describe run = show (length run) ++ take 1 run
+
+main = mapM_ print (iterate lookAndSay 1)           -- display sequence until interrupted