Haskell 010

haskell/Util/Primes.hs

@@ -0,0 +1,15 @@
+module Util.Primes where
+
+is_prime :: (Integral a) => a -> Bool
+is_prime n
+    | n == 1 = False
+    | n < 4 = True
+    | n `rem` 2 == 0 = False
+    | n < 9 = True
+    | n `rem` 3 == 0 = False
+    | otherwise = do
+        let f = sqrt (fromIntegral n)
+        let checkprime x = (n `rem` x == 0 || n `rem` (x + 2) == 0)
+        not (or (map checkprime (takeWhile (<= floor f) [5,11..])))
+
+primes = filter is_prime (2:[3,5..])

haskell/e007.hs

@@ -5,20 +5,7 @@ What is the 10001st prime number?
 -}
 
 import Text.Printf
-
+import Util.Primes (primes)
-is_prime :: (Integral a) => a -> Bool
-is_prime n
-    | n == 1 = False
-    | n < 4 = True
-    | n `rem` 2 == 0 = False
-    | n < 9 = True
-    | n `rem` 3 == 0 = False
-    | otherwise = do
-        let f = sqrt (fromIntegral n)
-        let checkprime x = (n `rem` x == 0 || n `rem` (x + 2) == 0)
-        not (or (map checkprime (takeWhile (<= floor f) [5,11..])))
-
-primes = filter is_prime (2:[3,5..])
 
 main = do
     printf "    6th prime: %d\n" (primes !! 5 :: Integer)

haskell/e010.hs

@@ -0,0 +1,12 @@
+{- Calculate the sum of all the primes below two million.
+
+The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
+Find the sum of all the primes below two million.
+-}
+
+import Text.Printf (printf)
+import Util.Primes (primes)
+
+main = do
+    printf "Sum of primes below        10: %d\n" (sum (takeWhile (<10) primes))
+    printf "Sum of primes below 2,000,000: %d\n" (sum (takeWhile (<2000000) primes))