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我正在尝试制作一个让用户操作数据库(文本文件)的程序。使io程序更模块化
在我发布的代码中,我只显示了2个菜单选项,即“createdb”和“deletedb”,以及一些我拼命使功能更紧凑的功能。但我的问题是该模式与所有其他菜单选项类似。我要求用户输入数据库的名称或“b”返回到菜单,然后检查文件是否存在。
有没有一种方法可以很容易地分开这个,使我的代码更紧凑?我尝试在菜单中做这个部分,并有选择功能类型
FilePath -> IO()
但是,然后我的菜单看起来非常可怕。以下是一小部分代码:
type Choice = (String, String, IO())
choices :: [Choice]
choices =
[("a", "create a database", createdb),
("b", "delete a database", deletedb),
("c", "insert an entry to a database", insert),
("d", "print a database", selectall),
("e", "select entries from a database", select),
-- more similiar choices
menu :: IO()
menu = do
(mapM_ putStrLn . map showChoice) choices
c <- get "Enter the letter corresonding to the action of choice:"
case filter ((== c) . fst3) choices of
[] -> back "Not a valid choice. Try again"
(_, _, f) : _ -> f
createdb :: IO()
createdb = do
n <- maybeName
if isNothing n then menu else do
let name = fromJust n
fp <- maybeFile name
if isJust fp
then back $ "Error: \"" ++ name ++ "\" already exist."
else do
cols <- get "Enter unique column names in the form n1,n2,...,n (No spaces):"
let spl = (splitOnComma . toLower') cols
case filter (== True) (hasDuplicates spl : map (elem ' ') spl) of
[] -> writeFile (name ++ ".txt") (cols ++ "\n")
_ -> back "Error: Column names must be unique and have no spaces."
deletedb :: IO()
deletedb = do
n <- maybeName
if isNothing n then menu else do
let name = fromJust n
fp <- maybeFile name
if isJust fp
then removeFile (fromJust fp)
else back $ "Error: Could not find " ++ name
maybeName :: IO (Maybe String)
maybeName = do
input <- get "Enter database name or 'b' to go back to the menu."
return $ case input of
"b" -> Nothing
_ -> Just input
maybeFile :: String -> IO (Maybe FilePath)
maybeFile name = do
let fn = name ++ ".txt"
exists <- doesFileExist fn
return $ if exists then Just fn else Nothing
back :: String -> IO()
back msg = do
putStrLn msg
menu
get :: String -> IO String
get msg = do
putStrLn msg
getLine
[代码评论](http://codereview.stackexchange.com/)可能是您的问题更好的地方。 – MasterMastic
谢谢! @MasterMastic – Amoz