IO操作嵌套在其他单元未执行 [英] IO action nested in other monads not executing
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问题描述
foobar :: IO（ParseResult [（String，String）]）
code> ParseResult是这里定义的monad： https://hackage.haskell.org/package/haskell-src-exts-1.13。 5 / docs / Language-Haskell-Exts-Parser.html＃t：ParseResult
运行此函数将导致不创建文件。
writeReport2 :: [Char] - > IO（ParseResult（IO（）））
writeReport2 name = do x< - foobar
return $ do y< - x
return $ do z< - （execLaTeXT.docAndGraph） y
renderFile fileName z
其中
fileName = name ++.tex
然而，代码：
writeReport :: t - > LaTeXT IO a - > IO（）
writeReport name report = createLatex>> = renderFile fileName
where
createLatex = execLaTeXT report
fileName =AAAAA++.tex
testFoo = [（| HaskellExample Example File \\\
|两个例子如下：\\\
\\\
>>> fib 10 \ 55 \\ n \\ n>>> putStrLn \foo \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\''是一件事：，fib = undefined），（\\\
|这是一件事：\\\
，fibar :: String - > Float）]
itWorks = writeReportAAAA.txt$ docAndGraph testFoo
将创建一个新文件。
两套代码类型检查。
解决方案
我可以在不修改的情况下使用 writeReport2
我认为你的问题可能是嵌套IO动作，它的返回值是 writeResport2 ！
为了使嵌套的 IO 动作变平，我不得不使用功能 join :: Monad m => m（m a） - > ： Control.Monad
<$ ma c $ c> main :: IO（）
main = join $ fromParseResult< $> writeReport2test
以下是我的完整代码：
{ - ＃LANGUAGE OverloadedStrings＃ - }
模块Main其中
import Language.Haskell.Exts.Parser
import Text.LaTeX.Base.Writer
import Text.LaTeX
import Data.String
import Control.Monad
foobar :: IO（ParseResult [（ String，String）]）
foobar = return（ParseOk testFoo）
testFoo = [（| HaskellExample示例File \\\
|下面给出了两个示例：\\\
\\\
>>>>>>>>>>>>>< putStrLn \foo \\ ，fib :: Int - > Int
）
，（\\\
| This is a thing：，fib = undefined）
，（\\\
|这是一件事：\ n，fibar :: String - > Float）
]
docAndGraph :: Monad m => [（String，String）] - > LaTeXT m（）
docAndGraph x = do
documentclass [] article
document $
raw（fromString（show x））
writeReport2 :: [ Char] - > IO（ParseResult（IO（）））
writeReport2 name = do
x< - foobar
return $ do
y< - x
return $ do
z< - （execLaTeXT。docAndGraph）y
renderFile fileName z
其中
fileName = name ++.tex
$ b $ main :: IO（）
main = join $ fromParseResult< $> writeReport2test
加载到GHCi：
$ stack ghci
io-action-nested-in-other-monads-not-executed-0.1.0.0：initial-build-steps（exe）
使用以下软件包配置GHCi：io-action-nested-in-other-monads-not-executed
使用主模块：1.打包'io-action-nested-in-other-monads-not-execution'组件exe：io-action-nested-in-other-monads-not-executable with main-is file：/ home / sven / dev / stackoverflow-questions / io-action-nested-in-other-monads-not-execution /src/Main.hs
GHCi，版本8.0.2：http://www.haskell.org/ghc/：？寻求帮助
从/home/sven/.ghc/ghci.conf加载GHCi配置
编译主（/ home / sven / dev / stackoverflow-questions / io-action-nested- in-other-monads-not-executed / src / Main.hs，解释）
好了，加载模块：Main。
从/ tmp / ghci22616 / ghci-script加载的GHCi配置
运行它：
λ主
创建此文件：
$ cat test.tex
\documentclass {article} \begin {document} [（| HaskellExample Example File \\\
|两个例子如下：\\\
\\\
>>> fib 10 \\\
55 \\\
\\\
>>> putStrLn \foo\\\\
bar\\\\
foo\\\
bar，fib :: Int - > Int），（\\\
| This is a thing：，fib =undefined），（\\\
|这是一件事：\ n，fibar :: String - > Float）] \end {document}％
我知道这不是问题的范围，但是您可以绕过嵌套 IO 如果你想的话，通过doinf这样做，例如：
writeReport3 :: [Char] - > IO（）
writeReport3 name = do
let fileName = name ++.tex
x < - foobar
case x of
ParseOk y - > do $ b $ z< - execLaTeXT（docAndGraph y）
renderFile fileName z
ParseFailed _ _ - >
return（）
main :: IO（）
main = writeReport3test
I have a
foobar :: IO (ParseResult [(String,String)])
ParseResult is a monad defined here: https://hackage.haskell.org/package/haskell-src-exts-1.13.5/docs/Language-Haskell-Exts-Parser.html#t:ParseResult
I want to take those strings and write them to a LaTeXT m () defined in https://hackage.haskell.org/package/HaTeX-3.17.1.0/docs/Text-LaTeX-Base-Writer.html
Running this function results in no file being created.
writeReport2 :: [Char] -> IO (ParseResult (IO ()))
writeReport2 name = do x <- foobar
return $ do y <- x
return $ do z <- (execLaTeXT.docAndGraph) y
renderFile fileName z
where
fileName = name ++ ".tex"
However the code:
writeReport :: t -> LaTeXT IO a -> IO ()
writeReport name report = createLatex >>= renderFile fileName
where
createLatex = execLaTeXT report
fileName = "AAAAA" ++ ".tex"
testFoo = [(" | HaskellExample Example File\n | Two examples are given below:\n\n >>> fib 10\n 55\n\n >>> putStrLn \"foo\\nbar\"\n foo\n bar ","fib :: Int -> Int"),("\n | This is a thing: ","fib = undefined"),("\n | This is a thing:\n","fibar :: String -> Float")]
itWorks = writeReport "AAAA.txt" $ docAndGraph testFoo
Will create a new file.
Both sets of code type check.
解决方案
I could get writeReport2 working without modification.
I think what might have been your problem is the nested IO action in the return value of writeResport2!
In order to flatten the nested IO actions, I had to use the function join :: Monad m => m (m a) -> m a from Control.Monad:
main :: IO ()
main = join $ fromParseResult <$> writeReport2 "test"
Here is my complete code:
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Language.Haskell.Exts.Parser
import Text.LaTeX.Base.Writer
import Text.LaTeX
import Data.String
import Control.Monad
foobar :: IO (ParseResult [(String, String)])
foobar = return (ParseOk testFoo)
testFoo = [ ( " | HaskellExample Example File\n | Two examples are given below:\n\n >>> fib 10\n 55\n\n >>> putStrLn \"foo\\nbar\"\n foo\n bar "
, "fib :: Int -> Int"
)
, ("\n | This is a thing: ", "fib = undefined")
, ("\n | This is a thing:\n", "fibar :: String -> Float")
]
docAndGraph :: Monad m => [(String, String)] -> LaTeXT m ()
docAndGraph x = do
documentclass [] article
document $
raw (fromString (show x))
writeReport2 :: [Char] -> IO (ParseResult (IO ()))
writeReport2 name = do
x <- foobar
return $ do
y <- x
return $ do
z <- (execLaTeXT . docAndGraph) y
renderFile fileName z
where
fileName = name ++ ".tex"
main :: IO ()
main = join $ fromParseResult <$> writeReport2 "test"
Loading into GHCi:
$ stack ghci
io-action-nested-in-other-monads-not-executing-0.1.0.0: initial-build-steps (exe)
Configuring GHCi with the following packages: io-action-nested-in-other-monads-not-executing
Using main module: 1. Package `io-action-nested-in-other-monads-not-executing' component exe:io-action-nested-in-other-monads-not-executing with main-is file: /home/sven/dev/stackoverflow-questions/io-action-nested-in-other-monads-not-executing/src/Main.hs
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/sven/.ghc/ghci.conf
[1 of 1] Compiling Main ( /home/sven/dev/stackoverflow-questions/io-action-nested-in-other-monads-not-executing/src/Main.hs, interpreted )
Ok, modules loaded: Main.
Loaded GHCi configuration from /tmp/ghci22616/ghci-script
And running it:
λ main
Creates this file:
$ cat test.tex
\documentclass{article}\begin{document}[(" | HaskellExample Example File\n | Two examples are given below:\n\n >>> fib 10\n 55\n\n >>> putStrLn \"foo\\nbar\"\n foo\n bar ","fib :: Int -> Int"),("\n | This is a thing: ","fib = undefined"),("\n | This is a thing:\n","fibar :: String -> Float")]\end{document}%
I know it is not the scope of the question, but you could circumvent the nested IO if you want, by doinf this, for example:
writeReport3 :: [Char] -> IO ()
writeReport3 name = do
let fileName = name ++ ".tex"
x <- foobar
case x of
ParseOk y -> do
z <- execLaTeXT (docAndGraph y)
renderFile fileName z
ParseFailed _ _ ->
return ()
main :: IO ()
main = writeReport3 "test"
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