Project Euler Problem 8

I guess I should warn that these Project Euler posts have spoilers, in case you want to try the problems yourself ☺. My Scala solution to problem 8:

val input = "73167176531330624919225119674426574742355349194934" +
"96983520312774506326239578318016984801869478851843" +
"85861560789112949495459501737958331952853208805511" +
"12540698747158523863050715693290963295227443043557" +
"66896648950445244523161731856403098711121722383113" +
"62229893423380308135336276614282806444486645238749" +
"30358907296290491560440772390713810515859307960866" +
"70172427121883998797908792274921901699720888093776" +
"65727333001053367881220235421809751254540594752243" +
"52584907711670556013604839586446706324415722155397" +
"53697817977846174064955149290862569321978468622482" +
"83972241375657056057490261407972968652414535100474" +
"82166370484403199890008895243450658541227588666881" +
"16427171479924442928230863465674813919123162824586" +
"17866458359124566529476545682848912883142607690042" +
"24219022671055626321111109370544217506941658960408" +
"07198403850962455444362981230987879927244284909188" +
"84580156166097919133875499200524063689912560717606" +
"05886116467109405077541002256983155200055935729725" +
"71636269561882670428252483600823257530420752963450"

val digits = input.map(_.asDigit).toArray

def multiply(index: Int) = digits.slice(index, index + 5)
    .foldLeft(1)(_*_)

val multiples: Stream[Int] = {
    def rec(n: Int): Stream[Int] = Stream.cons(multiply(n),
        if (n > digits.length - 5) Stream.empty else rec(n+1))
    Stream.cons(mult(0), rec(1))
}
println(Iterable.max(multiples))

For convenience, this specifies the input as a string, then uses RichChar.asDigit to create a corresponding array of integers. The multiply function uses left fold to multiply together sequences of five digits. The multiples value is a stream (lazy list) of the multiples of all groups of five consecutive digits from the input. And finally, the Iterable object provides a convenient method to find the maximum value in any Iterable containing Orderable things.