Find the smallest number of coins to represent all numbers between 1 and 99

coinset.hs

import Data.List

coins :: [Int]
coins = [1, 2, 5, 10, 20, 50]

type CoinSet = [Int]

-- | All coinsets of a given length
draw :: Int -> [CoinSet]
draw 0 = [[]]
draw n = [ c:cs | c <- coins, cs <- draw (n-1) ]

-- | Can a given coinset represent the number s?
represent :: CoinSet -> Int -> Bool
represent cs s = any (\css -> sum css == s) (subsequences cs)

-- | Can it represent all numbers from 1..99?
representAll :: CoinSet -> Bool
representAll cs = all (represent cs) [1..99]

-- | Find shortest coinset
shortest :: Maybe CoinSet
shortest = find representAll allCS
    where allCS = concatMap draw [1..]

main = print shortest