:: IO_a_ -> _ IO_ThreadId -package:breakpoint -is:exact -package:happstack-server

Generalized version of evaluate.

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
((),())

Lift a value into the Structure.

Examples

>>> pure 1 :: Maybe Int
Just 1

>>> pure 'z' :: [Char]
"z"

>>> pure (pure ":D") :: Maybe [String]
Just [":D"]

Lift a value.

Apply the control pure over a data applicative.

Lift a value.

Inject a value into the monadic type. This function should not be different from its default implementation as pure. The justification for the existence of this function is merely historic.

Inject a value into the monadic type.

Strict version of return because usually we don't need that extra thunk.