userError package:rebase

userError :: String -> IOError
rebase Rebase.Prelude
Construct an IOException value with a string describing the error. The fail method of the IO instance of the Monad class raises a userError, thus: 
instance Monad IO where
...
fail s = ioError (userError s)
UserError :: IOErrorType
rebase Rebase.Prelude
userErrorType :: IOErrorType
rebase Rebase.Prelude
I/O error that is programmer-defined.
isUserError :: IOError -> Bool
rebase Rebase.Prelude
A programmer-defined error value constructed using userError.
isUserErrorType :: IOErrorType -> Bool
rebase Rebase.Prelude
I/O error that is programmer-defined.