Is there a way to "unwrap" IO monad in Haskell inside another io action?-CodePudding

In particular I want to use pure Haskell functions on the results on console input. I'm curious if exists something like ? operator from rust. this snippet complains that words expect the type String, while its supplied wrapped into an io action. But i can't even use >>= operator since as far as i understand i cannot instantiate IO constructor directly. So, does it mean all the standard library functions can't work with io even in the scope of io action?

thing :: IO ()
thing = do
    let mbwords = words $ getLine ;

CodePudding user response：

Since Haskell is not designed to be totally useless, there must be a way. And there is more than one indeed.

What you looking for is something like this

main = do
  line <- getLine
  let mbwords = words line

or perhaps

main = do
  mbwords <- fmap words getLine

Note you use <- to "open" the monadic value inside the do-block, not let.

Also note instantiating IO constructors is not necessary as long as you have functions that return IO actions, such as print. You can express the same idea with

main = fmap words getLine >>= print

(of course you can use an arbitrary action of the right type instead of print).