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Editorial Team
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Asked: 2026-06-15T11:44:52+00:00

I find adding type hints useful for debugging, but I don’t know how to

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I find adding type hints useful for debugging, but I don’t know how to do that with the result of using <- on and IO action

action :: IO ()
    foo :: String --doesnt't compile
    foo <- getLine
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1 Answer

  1. Editorial Team

    You can’t do that because <- isn’t a declaration. You can either:

    action :: IO ()
action = do
    foo <- getLine :: IO String
    ...

    Or, with {-# LANGUAGE ScopedTypeVariables #-}:

    action :: IO ()
action = do
    foo :: String <- getLine
    ...
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