Data commit

Task/Fermat-numbers/Haskell/fermat-numbers.hs

@@ -0,0 +1,36 @@
+import Data.Numbers.Primes (primeFactors)
+import Data.Bool (bool)
+
+fermat :: Integer -> Integer
+fermat = succ . (2 ^) . (2 ^)
+
+fermats :: [Integer]
+fermats = fermat <$> [0 ..]
+
+--------------------------- TEST ---------------------------
+main :: IO ()
+main =
+  mapM_
+    putStrLn
+    [ fTable "First 10 Fermats:" show show fermat [0 .. 9]
+    , fTable
+        "Factors of first 7:"
+        show
+        showFactors
+        primeFactors
+        (take 7 fermats)
+    ]
+
+------------------------- DISPLAY --------------------------
+fTable :: String -> (a -> String) -> (b -> String) -> (a -> b) -> [a] -> String
+fTable s xShow fxShow f xs =
+  unlines $
+  s : fmap (((++) . rjust w ' ' . xShow) <*> ((" -> " ++) . fxShow . f)) xs
+  where
+    rjust n c = drop . length <*> (replicate n c ++)
+    w = maximum (length . xShow <$> xs)
+
+showFactors :: [Integer] -> String
+showFactors x
+  | 1 < length x = show x
+  | otherwise = "(prime)"