| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Control.Effect.Error
Synopsis
- data Error exc m k
- throwError :: (Member (Error exc) sig, Carrier sig m) => exc -> m a
- catchError :: (Member (Error exc) sig, Carrier sig m) => m a -> (exc -> m a) -> m a
- runError :: forall exc sig m a. (Carrier sig m, Effect sig, Monad m) => Eff (ErrorC exc m) a -> m (Either exc a)
- newtype ErrorC e m a = ErrorC {}
Documentation
throwError :: (Member (Error exc) sig, Carrier sig m) => exc -> m a Source #
Throw an error, escaping the current computation up to the nearest catchError (if any).
run (runError (throwError a)) == Left @Int @Int a
catchError :: (Member (Error exc) sig, Carrier sig m) => m a -> (exc -> m a) -> m a Source #
Run a computation which can throw errors with a handler to run on error.
Errors thrown by the handler will escape up to the nearest enclosing catchError (if any).
Note that this effect does not handle errors thrown from impure contexts such as IO,
nor will it handle exceptions thrown from pure code. If you need to handle IO-based errors,
consider if Resource fits your use case; if not, use liftIO with
try or use Catch from outside the effect invocation.
run (runError (pure a `catchError` pure)) == Right a
run (runError (throwError a `catchError` pure)) == Right @Int @Int a
run (runError (throwError a `catchError` (throwError @Int))) == Left @Int @Int a
runError :: forall exc sig m a. (Carrier sig m, Effect sig, Monad m) => Eff (ErrorC exc m) a -> m (Either exc a) Source #