弗雷格';s相当于Haskell';让我们来读一读
在标准库的控制台中,是否有类似于Haskell的弗雷格';s相当于Haskell';让我们来读一读,haskell,functional-programming,jvm-languages,frege,Haskell,Functional Programming,Jvm Languages,Frege,在标准库的控制台中,是否有类似于Haskell的getLine和read的Frege方法来解析输入 目前我是这样做的: import frege.IO getLine :: IO String getLine = do isin <- stdin isrin <- IO.InputStreamReader.new isin brin <- IO.BufferedReader.fromISR isrin line <- brin.readLine return
getLine
和read
的Frege方法来解析输入
目前我是这样做的:
import frege.IO
getLine :: IO String
getLine = do
isin <- stdin
isrin <- IO.InputStreamReader.new isin
brin <- IO.BufferedReader.fromISR isrin
line <- brin.readLine
return $ fromExceptionMaybe line
fromExceptionMaybe :: Exception (Maybe a) -> a
fromExceptionMaybe (Right (Just r)) = r
fromExceptionMaybe (Right _) = error "Parse error on input"
fromExceptionMaybe (Left l) = error l.getMessage
pure native parseInt java.lang.Integer.parseInt :: String -> Int
main _ = do
line <- getLine
println $ parseInt line
有关更多详细信息,请参见以下Ingo的回答。更新:在更新版本的Frege中提供I/O支持
从3.21.80版开始,我们在标准库中有更好的I/O支持:
- 运行时提供
和stdout
(缓冲,UTF8编码stderr
环绕java.io.printWriter
和java.lang.System.out
)和java.lang.System.err
(UTF8解码stdin
环绕java.io.BufferedReader
)java.lang.System.in
- 函数
,print
,println
,putStr
写入putChar
stdout
和getChar
从getLine
读取,并在文件末尾抛出异常stdin
- Java类(如
、PrintWriter
等)的弗雷格等价物在模块BufferedWriter
中定义,并自动导入。这样,就支持了更基本的功能。例如,Java.IO
的返回类型为BufferedReader.readLine
,并通过返回IO(可能是字符串)
来发出文件结束的信号,与Java对应方类似,在这种情况下,Java对应方返回Nothing
null
--- A simple grep
module examples.Grep where
--- exception thrown when an invalid regular expression is compiled
data PatternSyntax = native java.util.regex.PatternSyntaxException
derive Exceptional PatternSyntax
main [] = stderr.println "Usage: java examples.Grep regex [files ...]"
main (pat:xs) = do
rgx <- return (regforce pat)
case xs of
[] -> grepit rgx stdin
fs -> mapM_ (run rgx) fs
`catch` badpat where
badpat :: PatternSyntax -> IO ()
badpat pse = do
stderr.println "The regex is not valid."
stderr.println pse.getMessage
run regex file = do
rdr <- utf8Reader file
grepit regex rdr
`catch` fnf where
fnf :: FileNotFoundException -> IO ()
fnf _ = stderr.println ("Could not read " ++ file)
grepit :: Regex -> BufferedReader -> IO ()
grepit pat rdr = loop `catch` eof `finally` rdr.close
where
eof :: EOFException -> IO ()
eof _ = return ()
loop = do
line <- rdr.getLine
when (line ~ pat) (println line)
loop
——一个简单的grep
模块示例。Grep在哪里
---编译无效正则表达式时引发异常
data PatternSyntax=本机java.util.regex.PatternSyntaxException
派生异常模式语法
main[]=stderr.println“用法:java示例.Grep regex[文件…””
main(pat:xs)=do
rgx grepit rgx stdin
fs->mapM(运行rgx)fs
`抓住巴德帕特在哪里
badpat::模式语法->IO()
badpat=do
stderr.println“正则表达式无效。”
stderr.println pse.getMessage
运行regex file=do
rdr IO()
fnf_u2;=stderr.println(“无法读取”++文件)
grepit::Regex->BufferedReader->IO()
grepit pat rdr=loop`catch`eof`finally`rdr.close
哪里
eof::EOFEException->IO()
eof=返回()
循环=do
行,我自由添加了一些标签。非常感谢。弗雷格正在取得巨大的进步,如果我能帮上什么忙,我会很乐意为之做出贡献。@Marimuthu-请给我发封邮件,你可以在弗雷格项目页面上找到我的地址。(找不到你的。)当然可以。BufferedReader类型具有readLine函数。
--- A simple grep
module examples.Grep where
--- exception thrown when an invalid regular expression is compiled
data PatternSyntax = native java.util.regex.PatternSyntaxException
derive Exceptional PatternSyntax
main [] = stderr.println "Usage: java examples.Grep regex [files ...]"
main (pat:xs) = do
rgx <- return (regforce pat)
case xs of
[] -> grepit rgx stdin
fs -> mapM_ (run rgx) fs
`catch` badpat where
badpat :: PatternSyntax -> IO ()
badpat pse = do
stderr.println "The regex is not valid."
stderr.println pse.getMessage
run regex file = do
rdr <- utf8Reader file
grepit regex rdr
`catch` fnf where
fnf :: FileNotFoundException -> IO ()
fnf _ = stderr.println ("Could not read " ++ file)
grepit :: Regex -> BufferedReader -> IO ()
grepit pat rdr = loop `catch` eof `finally` rdr.close
where
eof :: EOFException -> IO ()
eof _ = return ()
loop = do
line <- rdr.getLine
when (line ~ pat) (println line)
loop