Util.hs

module Test.Util (
    showPowersOf10
  , showPowersOf
  ) where

import           Data.List (find)
import           Data.Maybe (fromJust)
import           Text.Printf

showPowersOf10 :: Int -> String
showPowersOf10 = showPowersOf 10

showPowersOf :: Int -> Int -> String
showPowersOf factor n
  | factor <= 1 = error "showPowersOf: factor must be larger than 1"
  | n < 0       = "n < 0"
  | n == 0      = "n == 0"
  | otherwise   = printf "%d <= n < %d" lb ub
  where
    ub = fromJust (find (n <) (iterate (* factor) factor))
    lb = ub `div` factor