brokenCalc.hs

getHalves :: Int -> [Int]
getHalves = takeWhile (/=0) . iterate (\x -> if x `mod` 2 == 0 then x `div` 2 else 0)

brokenCalc :: Int -> Int -> Int
brokenCalc s t = brokenCalc' 0 s t

brokenCalc' :: Int -> Int -> Int -> Int
brokenCalc' i s t
  | s == t = i
  | s `elem` halves   = brokenCalc' i' (s*2) t
  | s > (last halves) = brokenCalc' i' (s-1) t
  | otherwise         = brokenCalc' i' (s*2) t
  where halves = getHalves t
        i' = i+1

main = do
  print $ brokenCalc 3 10

gistfile1.txt

➜ runhaskell brokenCalc.hs
3