tabular.hs

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications    #-}

import Data.Semigroup
import Control.Arrow
import Data.Align
import Data.Coerce
import Data.Tuple

newtype Stream a = Stream [a]
instance Monoid a => Monoid (Stream a) where
    mempty = Stream []
    mappend = coerce (malign @[] @a)
    
zipLeft f  = foldr (\x k ~(y:ys) -> f x y : k ys) (const [])
pad = foldr (\x k n -> x : k (n-1)) (flip replicate ' ')

tabular :: [[String]] -> String
tabular = unlines . map unwords . loop (swap . uncurry f)
  where
    f xs (Stream ys) = traverse (first Stream . unzip . flip (zipLeft g) ys) xs
    g x (Max n) = (Max (length x), pad x n)
    
ex1 :: String
ex1 = tabular
    [ [ "foo", "bar" ]
    , [ "x", "xyzzy", "foo" ]
    , [ "sik", "kik", "tik" ]
    ]