使用具有两个列表而非一个列表的地图。你可以窝窝吗？ [英] Using map with two lists rather than one. Can you nest?

问题描述

我需要运行一个多次使用两个参数的函数。我有两个包含这些参数的列表，我希望能够使用 map 或类似的东西来调用具有相应参数的函数。

我想要调用的函数有这样的类型：

  runParseTest :: String  - >字符串 - > IO（）
  

这些列表是这样创建的：

   - 获取库目录中的文件列表
文件<  -  getDirectoryContentstests / libraries
  - 过滤掉..和 。并添加路径
 let names = filter（\ x  - > head x / ='。'）files 
 let libs = [tests / libraries /++ f | f < -  $ name> 
  

因此可以说名称包含 [test1.js，test2.js，test3.js] 和 libs 包含 [tests / libraries / test1.js，tests / libraries / test2.js，tests / libraries / test3.js]

我想这样称呼他们：

  runParseTesttest1.js tests / libraries / test1.js
 runParseTesttest2.jstests / libraries / test2.js
 runParseTesttest3.jstests / libraries / test3.js
  

我知道我可以创建一个辅助函数，它可以很容易地完成这项工作，但出于兴趣，是否可以在一行使用 map ？

这是我迄今为止的内容，但显然第一个参数始终是test ：

  mapM_（runParseTesttest）libs 
  

如果不清楚，我很抱歉。我可以提供更多的信息，如果有必要的话。

解决方案

c> [test1.js，test2.js，test3.js]
和libs包含 [tests / libraries / test1.js ，tests / libraries / test2.js，tests / libraries / test3.js]

我想给他们打电话这：

runParseTesttest1.jstests / libraries / test1.js
runParseTesttest2.jstests / libraries / test2.js
runParseTesttest3.jstests / libraries / test3。 js

可以用 zip ：

$ $ p $ map（\（a，b） - > runParseTest ab）$ zip名称库lib


也许 uncurry runParseTest ：

  map（uncurry runParseTest）$ zip名称库
  

或与 zipWith ：

  zipWith runParseTest names libs 
  

像Ozgur 表示，monads有一些类似物：

 > ：t zipWithM 
 zipWithM :: Monad m => （a  - > b  - > m c） - > [a]  - > [b]  - > m [c] 
> ：t zipWithM_ 
 zipWithM_ :: Monad m => （a  - > b  - > m c） - > [a]  - > [b]  - > m（）
  

I need to run a function that takes two arguments several times. I have two lists containing these arguments and I'd like to be able to use map or something similar to call the function with the corresponding args.

The function I want to call has this type:

runParseTest :: String -> String -> IO()

The lists are created like this:

-- Get list of files in libraries directory
files <- getDirectoryContents "tests/libraries"
-- Filter out ".." and "." and add path
let names = filter (\x -> head x /= '.') files
let libs = ["tests/libraries/" ++ f | f <- names]

So lets say that names contains ["test1.js", "test2.js", "test3.js"] and libs contains ["tests/libraries/test1.js", "tests/libraries/test2.js", "tests/libraries/test3.js"]

I want to call them like this:

runParseTest "test1.js" "tests/libraries/test1.js"
runParseTest "test2.js" "tests/libraries/test2.js"
runParseTest "test3.js" "tests/libraries/test3.js"

I know I could create a helper function that does this fairly easily, but out of interest, is it possible to do in one line using map?

This is what I have so far, but obviously the first argument is always "test":

mapM_ (runParseTest "test") libs

I apologise if this is unclear. I can provide more info if necessary.

解决方案

So lets say that names contains ["test1.js", "test2.js", "test3.js"] and libs contains ["tests/libraries/test1.js", "tests/libraries/test2.js", "tests/libraries/test3.js"]

I want to call them like this:

runParseTest "test1.js" "tests/libraries/test1.js" runParseTest "test2.js" "tests/libraries/test2.js" runParseTest "test3.js" "tests/libraries/test3.js"

It's possible to do that with zip:

map (\(a,b) -> runParseTest a b) $ zip names libs

Or maybe uncurry runParseTest:

 map (uncurry runParseTest) $ zip names libs

Or with zipWith:

 zipWith runParseTest names libs

And like Ozgur said, there are some analogues for monads:

> :t zipWithM
zipWithM :: Monad m => (a -> b -> m c) -> [a] -> [b] -> m [c]
> :t zipWithM_
zipWithM_ :: Monad m => (a -> b -> m c) -> [a] -> [b] -> m ()

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