need a better way to do "suffix"

gistfile1.hs

humanReadable :: Double -> Double -> Integer -> String
humanReadable num base power
  | num < 0    = "Negative file size!"
  | power > 8  = "Fucking huge!"
  | num > base = humanReadable (num / base) base (power + 1)
  | otherwise  = printf pstr num (suffix power)
  where
    pstr = if num > 10 then "%.0f%s" else "%.1f%s"
    suffix 0 = ""
    suffix 1 = "K" -- kilo
    suffix 2 = "M" -- mega
    suffix 3 = "G" -- giga
    suffix 4 = "T" -- tera
    suffix 5 = "P" -- peta
    suffix 6 = "E" -- exa
    suffix 7 = "Z" -- zetta
    suffix 8 = "Y" -- yotta
    suffix _ = "?"