strToInt and StrToDouble

fold_excersizes.hs

import Data.Char

strToInt :: String -> Int
strToInt [] = 0
strToInt (x:xs)
  | x == '-'  = - strToInt xs
  | otherwise = foldl step 0 (x:xs)
                where step acc x = acc * 10 + (digitToInt x)

strToDouble :: String -> Double
strToDouble [] = 0
strToDouble (x:xs) 
  | x == '-'  = left - right
  | otherwise = left + right
    where broken             = break (\x -> x == '.') (x:xs)
          left               = fromIntegral . strToInt $ fst broken
          right              = fraction . tail $ snd broken
          fraction (ys)      = foldr step 0 $ strToIntAry ys
          strToIntAry []     = [] 
          strToIntAry (z:zs) = (fromIntegral $ digitToInt z) : strToIntAry zs
          step acc n         = acc * 0.1 + n * 0.1