-- :cmd accepts an expr of type 'IO String'
let cmd = return "0"
:cmd cmd

-- works with multiline mode, handles indention correctly
:{
:cmd return $ unlines
  [ "1"
  , "2"
  ]
:}

-- it should work even 'IO' or 'String' is not in scope
import Prelude ()
:cmd cmd

-- or even when a different 'String' is in scope
import Prelude
type String = ShowS
:def macro \_ -> return id
:macro