2016 Update

Task/First-class-environments/Haskell/first-class-environments-1.hs

@@ -0,0 +1,4 @@
+hailstone n
+  | n == 1 = 1
+  | even n = n `div` 2
+  | odd n  = 3*n + 1

Task/First-class-environments/Haskell/first-class-environments-2.hs

@@ -0,0 +1,2 @@
+data Environment = Environment { count :: Int, value :: Int }
+                 deriving Eq

Task/First-class-environments/Haskell/first-class-environments-3.hs

@@ -0,0 +1 @@
+environments = [ Environment 0 n | n <- [1..12] ]

Task/First-class-environments/Haskell/first-class-environments-4.hs

@@ -0,0 +1,2 @@
+process (Environment c 1) = Environment c 1
+process (Environment c n) = Environment (c+1) (hailstone n)

Task/First-class-environments/Haskell/first-class-environments-5.hs

@@ -0,0 +1,5 @@
+process = execState $ do
+  n <- gets value
+  c <- gets count
+  when (n > 1) $ modify $ \env -> env { count = c + 1 }
+  modify $ \env -> env { value = hailstone n }

Task/First-class-environments/Haskell/first-class-environments-6.hs

@@ -0,0 +1,13 @@
+fixedPoint f x
+  | fx == x = [x]
+  | otherwise = x : fixedPoint f fx
+  where fx = f x
+
+prettyPrint field = putStrLn . foldMap (format.field)
+  where format n = (if n < 10 then " " else "") ++ show n ++ " "
+
+main = do
+  let result = fixedPoint (map process) environments
+  mapM_ (prettyPrint value) result
+  putStrLn (replicate 36 '-')
+  prettyPrint count (last result)

Task/First-class-environments/Haskell/first-class-environments-7.hs

@@ -0,0 +1,6 @@
+main = do
+  let result = map (fixedPoint process) environments
+  mapM_ (prettyPrint value) result
+  putStrLn (replicate 36 '-')
+  putStrLn "Counts: "
+  prettyPrint (count . last) result