Initial data commit

Task/Middle-three-digits/Haskell/middle-three-digits.hs

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+------------------- MIDDLE THREE DIGITS ------------------
+
+mid3 :: Int -> Either String String
+mid3 n
+  | m < 100 = Left "too small"
+  | even lng = Left "even number of digits"
+  | otherwise = Right . take 3 $ drop ((lng - 3) `div` 2) s
+  where
+    m = abs n
+    s = show m
+    lng = length s
+
+--------------------------- TEST -------------------------
+main :: IO ()
+main = do
+  let xs =
+        [ 123
+        , 12345
+        , 1234567
+        , 987654321
+        , 10001
+        , -10001
+        , -123
+        , -100
+        , 100
+        , -12345
+        , 1
+        , 2
+        , -1
+        , -10
+        , 2002
+        , -2002
+        , 0
+        ]
+      w = maximum $ length . show <$> xs
+  (putStrLn . unlines) $
+    (\n ->
+       justifyRight w ' ' (show n) <>
+       " -> " <> either (concat . ("(" :) . (: [")"])) id (mid3 n)) <$>
+    xs
+
+justifyRight :: Int -> Char -> String -> String
+justifyRight n c = (drop . length) <*> (replicate n c <>)