Haskell

Question

这是the problem的要点：

check_if_proceed configFolders = do
  let emacsdf = "/home/jacek/.emacs.d"
  traceM ("calling check_if_proceed " ++ show ("ccc",configFolders))
  exists <- doesDirectoryExist emacsdf
  symlink <- pathIsSymbolicLink emacsdf
  let confemp = configFolders == []
  let result = False
  if exists
    then do
    {
      if symlink
      then do
        {
          putStrLn ("This action will overwrite the existing symlink\n"++
                    "poinitng to " ++ "SOMEWHERE-FINISH ME\n\n" )
        }
      else do
        {
          putStrLn (emacsdf ++ " is not a symlink\n"++
                    "to use this utility, in your terminal do soemthing like:\n"++
                    "$ mv " ++ emacsdf ++ " " ++ emacsdf ++ "-alternative-config\n" ++
                    "exiting..." )
        }
    }
    else do
    {
      putStrLn ("no " ++ emacsdf ++ "found in your home folder")
      if confemp
      then do
        {
          putStrLn ("nor folders with the alternative emacs config\n" ++
                    "exiting..." )

        }
      else
        do {
          putStrLn "will try to symlink one of the found folders"
          }
    }

指示如何向其中添加 return 语句的奖励积分。

工作代码

这个 link 显示了一个可以工作的代码，它允许我使用命令式风格探索问题 space。

Answer 1

您缺少一个分号，在 line 31 上，在 putStrLn 和 if 之间：

    ....
    else do
    {
      putStrLn ("no " ++ emacsdf ++ "found in your home folder")
    ;                                                            -- HERE
      if confemp
      then do
        {
          putStrLn ("nor folders with the alternative emacs config\n" ++
                    "exiting..." )

        }
    ....

要遵循的模板是

    do { ... ; ... ; ... }

显式大括号和分号将防止由于代码中的错误缩进（可能是由于 tabs/spaces 问题）导致的任何解析错误。

完全显式 表示法总是在每个 do 块语句之间使用 ;。 if ... then ... else ... 弥补了一个表达式 / do 语句，即使分布在多行代码中也是如此。

Haskell - 如何嵌套包含多个 putStrLn 语句的多个 if 语句

Haskell - How do I nest multiple if statements containing multiple putStrLn satatements

syntax

do-notation

工作代码