By using return function we can turn a value into IO action. You can change String to IO String, You can change Int to Io Int etc.,
Prelude> :t return
return :: Monad m => a -> m a
Sample.hs
import Data.Char
getUpper :: String -> IO String
getUpper str = return (map toUpper str)
main = do
putStrLn "Enter String"
str <- getLine
result <- getUpper str
putStrLn $ "Result is " ++ result
$ ghc Sample.hs
[1 of 1] Compiling Main ( Sample.hs, Sample.o )
Linking Sample ...
$
$ ./Sample
Enter String
Hello Haskell
Result is HELLO HASKELL
Convert list of a to list of IO a
Sample.hs
liftToIO :: [a] -> [IO a]
liftToIO [] = []
liftToIO (x:xs) = (return x) : liftToIO xs
Prelude> :load Sample.hs
[1 of 1] Compiling Main ( Sample.hs, interpreted )
Ok, modules loaded: Main.
*Main>
*Main> let res1 = [1, 2, 3, 4]
*Main> :t res1
res1 :: Num t => [t]
*Main>
*Main> let res2 = liftToIO res1
*Main>
*Main> :t res2
res2 :: Num a => [IO a]
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