Formatting cells

Cell.hs

class Cell a where
    -- | Drop a number of characters from the left side. Treats negative numbers
    -- as zero.
    dropLeft :: Int -> a -> a

    -- | Drop a number of characters from the right side. Treats negative
    -- numbers as zero.
    dropRight :: Int -> a -> a

    -- | Drop characters from both sides. Treats negative numbers as zero.
    dropBoth :: Int -> Int -> a -> a
    dropBoth l r = dropRight r . dropLeft l

    -- | Returns the length of the visible characters as displayed on the
    -- output medium.
    visibleLength :: a -> Int

    -- | Measure the preceeding and following characters
    measureAlignment :: (Char -> Bool) -> a -> AlignInfo

    buildCell :: StringBuilder b => a -> b

class Semigroup a => StringBuilder a where
    stringB :: String -> a
    charB :: Char -> a
    replicateCharB :: Int -> Char -> a
    
instance StringBuilder String where
    string = id
    char = (: [])
    replicateChar = replicate

instance Cell String where
    dropLeft = drop
    dropRight n = reverse . drop n . reverse
    visibleLength = length
    measureAlignment p xs = case break p xs of
        (ls, s : rs) -> AlignInfo (length ls) $ Just (length rs)
        (ls, []) -> AlignInfo (length ls) Nothing

    buildCell = string