haskell: add [p12, p17]

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

haskell/Lib.hs

@@ -1,19 +1,39 @@
-module Lib (fib, primes, primeFactors) where
+module Lib
+  ( factors,
+    fib,
+    primes,
+    primeFactors,
+    sumOfDigits,
+  )
+where
+
+import Data.List (nub)
+
+factors :: Integral a => a -> [a]
+factors n = concat [if mod n f == 0 then nub [f, div n f] else [] | f <- [1 .. flsqrt n]]
 
 fib :: [Integer]
 fib = 1 : 2 : zipWith (+) fib (tail fib)
 
-isPrime :: Integer -> Bool
-isPrime n = n > 1 && null [[] | k <- [2 .. (floor $ sqrt $ fromIntegral n)], mod n k == 0]
+flsqrt :: Integral a => a -> a
+flsqrt n = floor $ sqrt $ fromIntegral n
+
+isPrime :: Integral a => a -> Bool
+isPrime n = n > 1 && null [[] | k <- [2 .. flsqrt n], mod n k == 0]
 
 primes :: [Integer]
 primes = 2 : filter isPrime [3, 4 ..]
 
-primeFactors :: Integer -> [Integer]
+primeFactors :: Integral a => a -> [a]
 primeFactors n = genPrimeFactors n 2
   where
-    genPrimeFactors :: Integer -> Integer -> [Integer]
+    genPrimeFactors :: Integral a => a -> a -> [a]
     genPrimeFactors n c
       | c * c > n = [n]
       | mod n c /= 0 = genPrimeFactors n (c + 1)
       | otherwise = c : genPrimeFactors (div n c) c
+
+sumOfDigits :: Integral a => a -> a
+sumOfDigits n
+  | n == 0 = 0
+  | otherwise = mod n 10 + sumOfDigits (div n 10)