在haskell中打印2D列表

Question

如果我有列表列表，并且我想要创建一个表，那么它们都对齐了，所有的列都对齐了。我开始了，但不知道怎么继续。

table xxs
    | length (nub [length xs | xs <- xxs])/=1 = error "not simetric"
    | otherwise = (mapM_ print) [ xs | xs <- xxs]

bignumber xxs = maximum [length (show (maximum xs))| xs<-xxs]

示例：

table [[1,2,456],[34,2,34]-->

  1   1 456
 34   2  34

Answer 1

您可以使用printf进行打印，也可以使用transpose计算列的maxlen。

import Text.Printf
import Data.List (transpose)

table = undefined

showtable xxs = mapM_ (showrow. zip maxlens) xxs
  where
    maxlens = map (show . (+ 1)) $ foldr (max.length.show) 0 $ transpose xxs
    showcell (maxl,c) = printf ("%" ++ ml ++ "s") $ show c
    showrow xs = mapM_ showcell xs >> putStrLn "" 

Answer 2

不如：

import Data.List

print_ x =  putStr $ (show x) ++ "\t" 

table xxs 
    | length (nub [length xs | xs <- xxs])/=1 = error "not simetric"
    | otherwise = mapM_ printRow xxs 
        where printRow xs =  (mapM_ print_) xs >> putStrLn "" 

演示：

table [[1,2,456],[34,2,34]]
1   2   456  
34  2   34