Reverse hash quest

reverse.hs

abc = "acdegilmnoprstuw"
pnum = 37

-- Solution 1
reverse_hash1 _ 0 = []
reverse_hash1 x len = (reverse_hash1 x' len') ++ [abc !! m]
  where 
    m = x `mod` pnum
    x' = (x - m) `div` pnum
    len' = len - 1

-- Solution 2
reverse_hash2 x len = map (abc !!) (base [] x) 
  where
    base a x
      | x == 0 = a
      | x == len = a
      | otherwise = base (r:a) q where (q,r) = x `divMod` pnum