Haskell IO system is super hard to understand for me so i have question : How to read from standard input to list ? I know that there is function getLine :: IO String and interact. But i do not know how to convert the input to list so I can use it in this three functions :

```
powerset [] = [[]]
powerset (x:xs) = xss ++ map (x:) xss
where xss = powerset xs
main = print $ powerset([1,2])
import Control.Monad(filterM)
p = filterM(const[True,False])
main = p[1,2]
main = subsequences([1,2])
```

I want to be able to write 1 2 3 and pass this values to the function. Can you tell/show how to do it ?

**Extra question**

Haskell is full of magic so i was wondering if it possible to use input directly in the function like this :

```
main = subsequences(some input magic here)
```

Answer:

You may write:

```
main = readLn >>= print . subsequences
```

You will need to nail down the type to be read, for example by having a monomorphic `subsequences`

or by annotating `readLn`

. In ghci:

```
Data.List> (readLn :: IO [Integer]) >>= print . subsequences
[1,2,3]
[[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]
```

(I typed in the first and second lines -- both followed by enter -- and the third line was the result.)

For more details, you may enjoy one of the excellent resources below:

- The IO Monad for People who Simply Don't Care
- You Could Have Invented Monads (And Maybe You Already Have)
- All About Monads

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