Is there any way to use IO Bool in if-statement without binding to a name in haskell?

Question

If I've got a function that returns IO Bool (specifically an atomically), is there any way to use the return value directly in the if statement, without binding?

So currently I've got

ok <- atomically $ do
  ...
if (ok) then do
  ...
else do
  ...

Is it at all possible to write this as something like

if (*some_operator_here* atomically $ do
      ...) then do
  ...
else do
  ...

I was hoping there'd be a way to use something like <- anonymously, i.e., if (<- atomically ...) but so far no such luck.

Similarly on getLine, is it possible to write something like

if ((*operator* getLine) == "1234") then do ...

Related addendum--what is the type of (<-)? I can't get it to show up in ghci. I'm assuming it's m a -> a, but then that would mean it could be used outside of a monad to escape that monad, which would be unsafe, right? Is (<-) not a function at all?

Answer 1

You can use ifM from Control.Conditional if that suits your purpose and its not even hard to write a similar function.

Just to give you example

import Control.Conditional
import Control.Monad

(==:) :: ( Eq a,Monad m) => m a -> m a -> m Bool
(==:) = liftM2 (==)

main = ifM (getLine ==: getLine) (print "hit") (print "miss")

I think there are ways using rebindable syntax extension that you can even use if c then e1 else e2 like syntax for ifM but it is not worth the effort to try that.