PureScript By Example - Write a fold to determine the largest and smallest files in the filesystem.

gistfile2.txt

onlyFiles :: Path -> Array Path
onlyFiles file = onlyFiles' file []
  where
    onlyFiles' file files | isDirectory file = do
      child <- ls file
      onlyFiles' child files
    onlyFiles' file files = file : files


safeMin :: Maybe Path -> Maybe Path -> Maybe Path
safeMin Nothing x = x
safeMin x Nothing = x
safeMin (Just x) (Just y) | size x < size y = Just x
safeMin (Just x) (Just y) = Just y

safeMax :: Maybe Path -> Maybe Path -> Maybe Path
safeMax Nothing x = x
safeMax x Nothing = x
safeMax (Just x) (Just y) | size x > size y = Just x
safeMax (Just x) (Just y) = Just y

smallestLargestFiles path =  foldl smallestLargest [Nothing, Nothing] (onlyFiles path)
  where
  smallestLargest [smallest, largest] file = do
    let smallest' = safeMin smallest (Just file)
        largest' = safeMax largest (Just file)
    [smallest', largest']