Data commit

Task/Anonymous-recursion/Haskell/anonymous-recursion-1.hs

@@ -0,0 +1,7 @@
+fib :: Integer -> Maybe Integer
+fib n
+  | n < 0 = Nothing
+  | otherwise = Just $ real n
+              where real 0 = 1
+                    real 1 = 1
+                    real n = real (n-1) + real (n-2)

Task/Anonymous-recursion/Haskell/anonymous-recursion-2.hs

@@ -0,0 +1,6 @@
+import Data.Function (fix)
+
+fib :: Integer -> Maybe Integer
+fib n
+  | n < 0 = Nothing
+  | otherwise = Just $ fix (\f -> (\n -> if n > 1 then f (n-1) + f (n-2) else 1)) n

Task/Anonymous-recursion/Haskell/anonymous-recursion-3.hs

@@ -0,0 +1,2 @@
+ghci> map fib [-4..10]
+[Nothing,Nothing,Nothing,Nothing,Just 1,Just 1,Just 2,Just 3,Just 5,Just 8,Just 13,Just 21,Just 34,Just 55,Just 89]

Task/Anonymous-recursion/Haskell/anonymous-recursion-4.hs

@@ -0,0 +1,23 @@
+fib :: Integer -> Maybe Integer
+fib n
+  | n < 0 = Nothing
+  | otherwise =
+    Just $
+    (\f ->
+        let x = f x
+        in x)
+      (\f n ->
+          if n > 1
+            then f (n - 1) + f (n - 2)
+            else 1)
+      n
+
+-- TEST ----------------------------------------------------------------------
+main :: IO ()
+main =
+  print $
+  fib <$> [-4 .. 10] >>=
+  \m ->
+     case m of
+       Just x -> [x]
+       _ -> []