Rebase laster some tests

src/3n+1/Main.hs

@@ -3,29 +3,17 @@ The Simplest Math Problem No One Can Solve - Collatz Conjecture
 https://youtu.be/094y1Z2wpJg
 -}
 
-import           Control.Parallel.Strategies (parMap, rdeepseq, rpar)
 import           Data.Set    (fromList)
 import           Debug.Trace (trace)
 
 main :: IO ()
 main = do
-  let results =
-            parMap rdeepseq f [10^100_000..10^100_000+100] :: [Integer]
+  let results = map f [10^1_000..10^1_000+100] :: [Integer]
   print (fromList results)
--- main = print $ fromList $ dxs
--- main = print $ fromList $ take 300 $ map f [2^100_000..]
-  -- fromList [100001,717859]
-
--- main = print $ fromList $ take 3 $ map f [2^310997..]
--- main = print $ f $ 2^310997 + 2
 
 lst :: [Integer]
 lst = take 300 [2^100_000..]
 
-dxs :: [Integer]
-dxs = parMap rpar f lst
-
-
 f :: Integer -> Integer
 f n = s 1 n
   where
@@ -71,3 +59,5 @@ cc n = cc' [] n
       | even n = cc' acc' (n `div` 2)
       | odd  n = cc' acc' (3*n + 1)
       where acc' = acc <> [n]
+
+x = map (length . cc) [2^1_000+10..]

src/3n+1/collatzChainPost.lhs

@@ -0,0 +1,81 @@
+= Collatz Chains in Haskell
+
+== Title header
+
+This is a literate haskell blog post. You can load and run this code!
+
+The Simplest Math Problem No One Can Solve - Collatz Conjecture
+<https://youtu.be/094y1Z2wpJg>
+
+Why do we want to do this?
+
+> collatzStep :: Integer -> Integer
+> collatzStep n
+>   | even n = n `div` 2
+>   | odd  n = 3 * n + 1
+
+With this, we can iterate over it.
+
+> collatzStep' :: Integer -> Integer
+> collatzStep' n
+>   | n == 1 = error "done"
+>   | even n = n `div` 2
+>   | odd  n = 3 * n + 1
+
+> result :: [Integer]
+> result = iterate collatzStep' 5
+
+
+collatz collect
+generate the collatz sequence and return it
+
+> cc :: Integer -> [Integer]
+> cc n = cc' [] n
+>   where
+>     cc' :: [Integer] -> Integer -> [Integer]
+>     cc' acc n
+>       | n ==    1  = acc <>   [1]
+>       | n ==    0  = acc <>   [0]
+>       | n ==  (-1) = acc <>  [-1]
+>       | n ==  (-5) = acc <>  [-5]
+>       | n == (-17) = acc <> [-17]
+>       | even n = cc' acc' (n `div` 2)
+>       | odd  n = cc' acc' (3*n + 1)
+>       where acc' = acc <> [n]
+
+> a :: [Integer]
+> a = reverse $ cc $ 2^1_000+1
+
+> b :: [Integer]
+> b = reverse $ cc $ 2^1_000+2
+
+> comparingChains :: [Bool]
+> comparingChains = zipWith (==) a b
+
+Now if we collect the chain lengths of large numbers we see something slightly horrifying:
+
+> x = map (length . cc) [2^1_000+10..]
+
+This prints us the list of lengths of the chain as:
+[7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7430,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249,7249...]
+
+λ> cc 13
+[13,40,20,10,5,16,8,4,2,1]
+λ> cc 12
+[12,6,3,10,5,16,8,4,2,1]
+
+Now this makes sense with small numbers.
+But I find it weird with large numbers.
+
+> f :: Integer -> Integer
+> f n = s 1 n
+>   where
+>     s :: Integer -> Integer -> Integer
+>     s i n
+>       | n ==    1  = i
+>       | n ==    0  = i
+>       | n ==  (-1) = i
+>       | n ==  (-5) = i
+>       | n == (-17) = i
+>       | even n = s (succ i) (n `div` 2)
+>       | odd  n = s (succ i) (3 * n + 1)