Question

Hey。关于本周的辅导,其中一个问题要求采用其他功能格式Line和格式List编制一个行文清单,从而形成一种功能格式。

我的法典就是这样做的。

type Line = String

formatLine :: Line -> String
formatLine l = l ++ "
"

formatList :: (a -> String) -> [a] -> String
formatList f [] = []
formatList f xs = f (head xs) ++ formatList f (tail xs)

formatLines :: [Line] -> String
formatLines xs = formatList formatLine xs

The code seems (to me, at least) like it should work, but instead of creating a new line where " " is, gets appended to the string.

任何帮助都将受到高度赞赏。

Answer 1

这是因为你可能使用印刷结果。相反,使用putStr。观察:

Prelude> print "test
test
"
"test
test"
Prelude> putStr "test
test
"
test
test

除此以外,您可使用对应方式在以下网址上填写:formatList,但>>>>>>>> >>>>>>>>>>>和

formatList :: (a -> String) -> [a] -> String
formatList f [] = []
formatList f (x:xs) = f x ++ formatList f xs

但是,实际上没有必要界定<代码>formatList yourself,因为它与。

formatList :: (a -> String) -> [a] -> String
formatList = concatMap

Combining all this, you can also just write (note that (++ " ") is a section):

formatLines :: [String] -> String
formatLines = concatMap (++ "
")

http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3Aunlines”rel=“noreferer”>unlines:

formatLines :: [String] -> String
formatLines = unlines

Answer 2

公正的审判

formatLines = unwords

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