mindent.hs

-- Naïve indenter

space = repeat ' '

_indent :: Int -> [Int] -> [Char] -> [Char]
_indent _ _ [] = ""
_indent w k@(t:_) (',':s) = '\n' : take t space ++ ',' : _indent (t+1) k s
_indent w k (c:s) = c : _indent (w+1) (f c) s
  where
    f v
      | c == '{' || c == '[' = (w:k)
      | c == '}' || c == ']' = drop 1 k
      | otherwise = k

indent :: String -> String
indent = _indent 0 []