Add solution for problem 60.

Problem060.hs

@@ -0,0 +1,24 @@
+-- Find the lowest sum for a set of five primes for which any two primes
+-- concatenate to produce another prime.
+
+import Euler
+import Debug.Trace
+import Data.Array.Unboxed ((!))
+
+nDigits n = ceiling $ logBase 10 $ max 1 $ fromIntegral n
+a ## b = (a * (10 ^ nDigits b)) + b
+
+main = print $ head $ do
+   a <- drop 4 primes
+   b <- takeWhile (< a) primes
+   guard $ all isPrime $ [(## b), (b ##)] <*> [a]
+   --traceM $ show (a,b)
+   c <- takeWhile (< b) primes
+   guard $ all isPrime $ [(## c), (c ##)] <*> [a,b]
+   --traceM $ show (a,b,c)
+   d <- takeWhile (< c) primes
+   guard $ all isPrime $ [(## d), (d ##)] <*> [a,b,c]
+   e <- takeWhile (< d) primes
+   guard $ all isPrime $ [(## e), (e ##)] <*> [a,b,c,d]
+   let xs = [a,b,c,d,e]
+   return (sum xs, xs)