haskell - 在 Haskell 程序之间传递数据

Question

我正在 Haskell 中编写两个程序，其中一个提供了一棵充满值的树。

另一个程序现在必须填充同一棵树。我搜索了它，但我还没有找到关于如何做类似事情的信息。

例如，我执行 ./Generate ，它会保存树的值。然后我执行 ./Work 它会使用树的值。有人可以帮我吗？

Answer 1

最简单的方法可能是

data MyData = ... deriving (Read, Show)

制作人

makeMyData :: MyData
makeMyData = ....

main = writeFile "output.data" (show makeMyData)

消费者

ioUseMyData :: MyData -> IO ()
ioUseMyData myData = ....

main = readFile "output.data" >>= ioUseMyData . read

您可以使用 getContents 和 putStrLn 来使用标准输入/输出。

完整示例:

-- probably as module
data Tree = Node { value :: Int
                 , left  :: Tree
                 , right :: Tree
                 }
          | Empty
            deriving (Read, Show)

-- your producer program
producerProgram = do

    let makeTree = Node 3 (Node 5 Empty Empty) (Node 7 Empty Empty)
    writeFile "output.data" (show makeTree)

-- your consumer program
consumerProgram = do

    let ioUseTree t = do

            let countNodes Empty = 0
                countNodes (Node _ l r) = 1 + countNodes l + countNodes r

            putStrLn $ "Tree with " ++ show (countNodes t) ++ " nodes"

    readFile "output.data" >>= ioUseTree . read

-- simulate call both
main = do

    -- produce
    producerProgram

    -- consume
    consumerProgram

结果

Tree with 3 nodes

更换

writeFile "output.data" (show makeTree)

由

print makeTree

和

readFile "output.data" >>= ioUseTree . read

由

getContents >>= ioUseTree . read

您可以使用管道(bash、cmd.exe、...)

$ ./producer | ./consumer
Tree with 3 nodes