:: Monad m => String -> m a -package:universum

Fail with a message. This operation is not part of the mathematical definition of a monad, but is invoked on pattern-match failure in a do expression. As part of the MonadFail proposal (MFP), this function is moved to its own class MonadFail (see Control.Monad.Fail for more details). The definition here will be removed in a future release.

throws ExpectFailed. This is nice for writing your own abstractions.

Throw an error, escaping the current computation up to the nearest catchError (if any).

runThrow (throwError e >>= k) = runThrow (throwError e)

Like throwEnvelopeErr but without providing a message.

>>> import Control.Monad.Except (runExcept)

>>> throwEnvelopeErr "BAD_ERROR" "a very bad error occurred!" :: Either (Err String) Int
Left (Err {errErr = "BAD_ERROR", errExtra = Just "a very bad error occurred!"})

A higher-order generalisation of replicate. For example

foo :: IO (String, String, String)
foo = replicateT getLine

> foo
Hello
world
!
("Hello","world","!")

Use sequenceT instead. It has a better name.

A higher-order generalisation of sequenceA. For example

> sequenceT (print 3110, putStrLn World) :: IO ((), ())
3110
World
((),())

A convenience function for throwing a user error. This is useful for cases where it would be too high a burden to define your own exception type. This throws an exception of type StringException. When GHC supports it (base 4.9 and GHC 8.0 and onward), it includes a call stack.

Lifted throwErrno.

Lifted version of die.

>>> die "Goodbye!"
Goodbye!
*** Exception: ExitFailure 1

When you encounter an error where the only sane way to handle it is to write an error to the log and die messily, use fatalError. This is a good candidate for things like not being able to find configuration files on startup.