Could anyone tell me why this might be happening? I was trying to add some modules to the GHCi(:d +...).

    Couldn't match expected type `String -> IO String'
           against inferred type `()'
    In the expression: ()
    In the expression: () :: String -> IO String
    In the definition of `__cmCompileExpr':
        __cmCompileExpr = () :: String -> IO String

Thank you.