我可以在Show中使用表格和换行符之类的特殊字符吗? [英] Can I use special characters like tabulations and newlines in Show?

问题描述

data Pair = P Int Int

instance Show Pair where
  show (P n1 n2) = (show n1) ++ "\t" ++ (show n2)

结果:

GHCi, version 7.6.3: http://www.haskell.org/ghc/  :? for help
\Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( labn.hs, interpreted )
Ok, modules loaded: Main.
*Main> show (P 5 6)
"5\t6"

好了，这可能是一个人为的问题，但是我的实际用例是尝试漂亮地打印一棵树-在其中换行符和选项卡似乎有助于可读性.

OK for a pair of ints this might be an artificial problem, but my actual use case is trying to pretty print a tree - where newlines and tabs seem instrumental for readability.

我可以在 show 中以某种方式使用这些字符吗?

Can I somehow use these characters with show?

推荐答案

show 返回一个字符串，然后将其放在GHCi中时，它会执行 print.显示$(P 5 6)，它等效于 putStrLn.表演 .显示$(P 5 6)，它将打印所有字符.

show returns a string, and then when you put that in GHCi, it does print . show $ (P 5 6), which is equivalent to putStrLn . show . show $ (P 5 6) which will print all the characters.

问题在于双重演出.

您要做的是仅使用打印，如 print(P 5 6).如果您使用的是GHCi，则 print 会自动应用于每个表达式，因此您只需要键入

What you want to do is use print only, as print (P 5 6). If you're using the GHCi, print is automatically applied to every expression, so you only need to type

Prelude> P 5 6

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