| Copyright | (c) 2012--2021 The University of Kansas |
|---|---|
| License | BSD3 |
| Maintainer | Neil Sculthorpe <neil.sculthorpe@ntu.ac.uk> |
| Stability | beta |
| Portability | ghc |
| Safe Haskell | Safe-Inferred |
| Language | Haskell2010 |
Language.KURE.MonadCatch
Description
This module provides classes for catch-like operations on Monads.
Synopsis
- class MonadFail m => MonadCatch m where
- data KureM a
- runKureM :: (a -> b) -> (String -> b) -> KureM a -> b
- fromKureM :: (String -> a) -> KureM a -> a
- liftKureM :: MonadFail m => KureM a -> m a
- liftAndCatchIO :: (MonadCatch m, MonadIO m) => IO a -> m a
- (<+) :: MonadCatch m => m a -> m a -> m a
- catchesM :: (Foldable f, MonadCatch m) => f (m a) -> m a
- tryM :: MonadCatch m => a -> m a -> m a
- mtryM :: (MonadCatch m, Monoid a) => m a -> m a
- attemptM :: MonadCatch m => m a -> m (Either String a)
- testM :: MonadCatch m => m a -> m Bool
- notM :: MonadCatch m => m a -> m ()
- modFailMsg :: MonadCatch m => (String -> String) -> m a -> m a
- setFailMsg :: MonadCatch m => String -> m a -> m a
- prefixFailMsg :: MonadCatch m => String -> m a -> m a
- withPatFailMsg :: MonadCatch m => String -> m a -> m a
Monads with a Catch
class MonadFail m => MonadCatch m where Source #
Monads with a catch for fail.
The following laws are expected to hold:
fail msg `catchM` f == f msg return a `catchM` f == return a
Instances
| MonadCatch IO Source # | The String is generated by |
| MonadCatch KureM Source # | |
| MonadCatch m => MonadCatch (OneR m) Source # | |
| MonadCatch m => MonadCatch (AnyR m) Source # | |
| MonadCatch m => MonadCatch (Transform c m a) Source # | Lifting through a Reader transformer, where (c,a) is the read-only environment. |
The KURE Monad
KureM is the minimal structure that can be an instance of MonadCatch.
The KURE user is free to either use KureM or provide their own monad.
KureM is essentially the same as Either String, except that it supports a MonadCatch instance which Either String does not (because its fail method calls error)
A major advantage of this is that monadic pattern match failures are caught safely.
fromKureM :: (String -> a) -> KureM a -> a Source #
Get the value from a KureM, providing a function to handle the error case.
The IO Monad
liftAndCatchIO :: (MonadCatch m, MonadIO m) => IO a -> m a Source #
Lift a computation from the IO monad, catching failures in the target monad.
Combinators
(<+) :: MonadCatch m => m a -> m a -> m a infixl 3 Source #
A monadic catch that ignores the error message.
catchesM :: (Foldable f, MonadCatch m) => f (m a) -> m a Source #
Select the first monadic computation that succeeds, discarding any thereafter.
tryM :: MonadCatch m => a -> m a -> m a Source #
Catch a failing monadic computation, making it succeed with a constant value.
mtryM :: (MonadCatch m, Monoid a) => m a -> m a Source #
Catch a failing monadic computation, making it succeed with mempty.
attemptM :: MonadCatch m => m a -> m (Either String a) Source #
Catch a failing monadic computation, making it succeed with an error message.
testM :: MonadCatch m => m a -> m Bool Source #
Determine if a monadic computation succeeds.
notM :: MonadCatch m => m a -> m () Source #
Fail if the monadic computation succeeds; succeed with () if it fails.
modFailMsg :: MonadCatch m => (String -> String) -> m a -> m a Source #
Modify the error message of a failing monadic computation. Successful computations are unaffected.
setFailMsg :: MonadCatch m => String -> m a -> m a Source #
Set the error message of a failing monadic computation. Successful computations are unaffected.
prefixFailMsg :: MonadCatch m => String -> m a -> m a Source #
Add a prefix to the error message of a failing monadic computation. Successful computations are unaffected.
withPatFailMsg :: MonadCatch m => String -> m a -> m a Source #
Use the given error message whenever a monadic pattern match failure occurs.