Question

我最近接到了一项我已经完成的任务，目前我需要一些帮助。

我需要实现的第一个功能是lookUp，split，combine和keyWordDefs。

然后我必须实现一个函数expand :: FileContents - ＆gt; FileContents - ＆gt; FileContents获取文本文件和信息文件的内容，并使用上述函数组合它们以构建表示输出文件的字符串。

到目前为止，这是我的代码：

module MP where

import System.Environment

type FileContents = String

type Keyword      = String
type KeywordValue = String
type KeywordDefs  = [(Keyword, KeywordValue)]

separators :: String
separators
  = " \n\t.,:;!\"\'()<>/\\"

lookUp :: String -> [(String, a)] -> [a]
-- Given a search string and a list of string/item pairs, returns
-- the list of items whose associated string matches the search string.
lookUp x y = [a|(b,a) <- y, x==b]

split :: String -> String -> (String, [String])
-- Breaks up a string.
split as [] = ("",[""])
split as (b:bs)
    | elem b as = (b:xs,"":y:ys)
    | otherwise = (xs, (b:y):ys)
         where
          (xs,y:ys) = split as bs

combine :: [Char] -> [String] -> [String]
-- Combines the components of a string from its constituent separator
-- characters and words, as generated by a call to split.
combine [] y = y
combine (x:xs)(y:ys) = y : [x] : combine xs ys

getKeywordDefs :: [String] -> KeywordDefs
-- Takes the contents of an information file in the form of a list
-- of lines and which returns a list of keyword/definition pairs.
getKeywordDefs [] = []
getKeywordDefs (x:xs) = (keyword, concat defs) : getKeywordDefs xs
  where
    (_, (keyword : def)) = split " " x
    defs = combine spaces def
    spaces = [ ' ' | s <- [2..length def]]

expand :: FileContents -> FileContents -> FileContents

扩展功能的一个例子是：

expand "The capital of $1 is $2" "$1 Peru\n$2 Lima."
"The capital of Peru is Lima."

我认为如果在输入字符串中有一个“$”，那么第一次查找（使用函数lookUp），然后拆分单词，然后用第二个输入替换以“$”开头的单词字符串，然后再将它们组合在一起？实际上我真的很困惑，我想知道这里是否有人了解函数扩展是如何工作的。

欢迎任何帮助：）

Answer 1

您的展开功能应如下所示：

-- It's probably better to change the type signature a little bit
-- because we're not returning the contents of a file, we're returning a string.
expand :: FileContents -> FileContents -> String
expand fc1 fc2 = let
    keywordDefs = getKeywordDefs fc2
    in replaceSymbols fc1 keywordDefs

然后你需要一个名为replaceSymbols的函数，它会在看到$ X时拆分fc1，然后用$ X代替在keywordDefs中查找$ X的结果。

replaceSymbols :: FileContents  -> KeywordDefs -> String

如果您仍需要帮助，请继续执行该功能并回复此答案：）。

Haskell扩展功能

1 个答案: