doubleMe x = x + x

doubleUs x y = doubleMe x + doubleMe y

doubleSmallNumber x = if x > 100
                        then x
                        else x*2

doubleSmallNumber' x = (if x > 100 then x else x*2) + 1

boomBangs xs = [if x < 10 then "BOOM!" else "BANG!" | x <- xs, odd x]

length' xs = sum [1 | _ <- xs]

removeNonUppercase :: [Char] -> [Char]
removeNonUppercase st = [c | c <- st, c `elem` ['A'..'Z']]

circumference :: Float -> Float
circumference r = 2 * pi * r

circumference' :: Double -> Double
circumference' r = 2 * pi * r