wl-pprint-extras中的可选空间和多个备选项 [英] Optional spaces and multiple alternatives in wl-pprint-extras

问题描述

是否有一种很好的/可接受的方式来获得两种以上的可选布局，特别是支持可选空间的方式？

特别是，我可能想要打印以下列三种方式之一列出：

  [1，2，3，4，5] 
 
 [1,2,3,4,5] 
 
 [1 
，2 
，3 
，4 
，5 
 ] 
  

按优先顺序排列。

解决方案

你可以在 group 和 flatAlt / p>

 （< |>）:: Doc e  - >文件e  - > Doc e 
 a< |> b = group $ flatAlt b a 
 
 infixl 5< |> 
  

我们将定义您的三个示例。

  { - ＃LANGUAGE OverloadedStrings＃ - } 
 
 import Text.PrettyPrint.Free 
 import System.IO 
 
 items = map char ['1'..'5'] 
 
最宽=括号。 hcat。标点符号，$ items 
 wide =括号。 hcat。标点符号，$ items 
 skinny =括号。 hcat。点缀，。 map（\ x  - ><> x> linebreak）$ items 
  

这些适合在屏幕上的宽度最大的是 widestFits ，可以用< |>

  widestFits = widest< |>宽< |>我们将尝试在三个文档上打印这些文档，其中一个文档足够宽以容纳<$ c 
 $ b  

c> widest 例子，只有一个宽度足以容纳 wide 示例，另一个不能容纳。

  main = do 
 displayIO stdout $ renderPretty 1.0 15 widestFits 
 putStrLn
 displayIO stdout $ renderPretty 1.0 14 widestFits 
 putStrLn
 displayIO stdout $ renderPretty 1.0 10 widestFits 
 putStrLn
  

  [1，2，3，4，5] 
 [ 1,2,3,4,5] 
 [1 
，2 
，3 
，4 
，5 
] 
  

Is there a good/accepted way to get more than two alternative layouts, specifically in a way which supports optional spaces?

In particular, I might want to print a list in one of three ways:

[1, 2, 3, 4, 5]

[1,2,3,4,5]

[ 1
, 2
, 3
, 4
, 5
]

in that order of preference.

解决方案

You can try one alternatives before another with group and flatAlt.

(<|>) :: Doc e -> Doc e -> Doc e
a <|> b = group $ flatAlt b a

infixl 5 <|>

We'll define your three examples.

{-# LANGUAGE OverloadedStrings #-}

import Text.PrettyPrint.Free
import System.IO

items = map char ['1'..'5']

widest = brackets . hcat . punctuate ", " $ items
wide   = brackets . hcat . punctuate ","  $ items
skinny = brackets . hcat . punctuate "," . map (\x -> " " <> x <> linebreak) $ items

The widest of these that fits on the screen, widestFits, can be defined in terms of <|> which we defined above.

widestFits = widest <|> wide <|> skinny

We will try pretty printing these on three documents, one wide enough to hold the widest example, one only wide enough to hold the wide example, and one that can't hold either.

main = do
    displayIO stdout $ renderPretty 1.0 15 widestFits
    putStrLn ""
    displayIO stdout $ renderPretty 1.0 14 widestFits   
    putStrLn "" 
    displayIO stdout $ renderPretty 1.0 10 widestFits
    putStrLn "

This results in the desired output.

[1, 2, 3, 4, 5]
[1,2,3,4,5]
[ 1
, 2
, 3
, 4
, 5
]

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