Reflect exceptions using phantom types. https://github.com/trskop/tagged-exception-core

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BSD3 licensed by Peter Trško
Maintained by peter.trsko@gmail.com

Tagged Exception Core

Hackage Hackage Dependencies [Haskell Programming Language][Haskell.org] [BSD3 License][tl;dr Legal: BSD3]



Reflect exceptions using phantom types. This library provides core API and others may build on top of it.

Usage Example

Example of reflecting reised exception in type:

{-# LANGUAGE DeriveDataTypeable #-}

import Control.Exception (Exception)

import Control.Monad.TaggedException (Throws)
import qualified Control.Monad.TaggedException as E (liftT, throw)
import Data.Typeable (Typeable)

data NotReady = NotReady String
    deriving (Show, Typeable)
        -- Both required by Exception class

instance Exception NotReady

myFunction :: Input -> Throws NotReady IO Output
myFunction input = do

    -- ... some stuff ...

    -- isReady :: Input -> IO Bool
    ready <- E.liftT $ isReady input
    unless ready
        . E.throw $ NotReady "Resource of myFunction is not ready."

    -- ... some other stuff ...


The BSD 3-Clause License, see [LICENSE][] file for details.


Contributions, pull requests and bug reports are welcome! Please don't be afraid to contact author using GitHub or by e-mail.

http://hackage.haskell.org/package/tagged-exception-core "tagged-exception-core package on Hackage" [Haskell.org]: http://www.haskell.org "The Haskell Programming Language" [LICENSE]: https://github.com/trskop/tagged-exception-core/blob/master/LICENSE "License of endo package." [tl;dr Legal: BSD3]: https://tldrlegal.com/license/bsd-3-clause-license-%28revised%29 "BSD 3-Clause License (Revised)"


ChangeLog / ReleaseNotes


  • Deprecating module Control.Monad.TaggedException.Utilities, definitions from it were moved in to Control.Monad.TaggedException.Core. (change)
  • Type Throws has now instance for Generic1, but only on GHC >=7.10, due to PolyKinds. (new)
  • HiddenException instances for AllocationLimitExceeded and Void, both defined in base >=4.8. (new)
  • HiddenException instance for TypeError, defined in base >=4.9. (new)
  • Bumped upper bound of [transformers][] package to include 0.5.* branch. (change)


  • Relaxing upper bound on exceptions package to include versions up to 0.8.*. (new)
  • Not uploaded on to [Hackage][], instead opted to modify package metadata of release.


  • Builds on GHC from 7.4 to 7.10, later with base 4.8. (change)
  • Bumping [transformers][] bounds to include 0.4.* versions. (change)
  • Dropped last threads of support for base <= 4.5; it hadn't worked anyway since exceptions ==0.6 depend on base >=4.5 && <5. (breaking change)
  • Instances for [mtl][] >=2.1 package. Package exceptions already depends on [mtl][], so it doesn't make sense to shy away from them. (new)
  • Introduced unsafe functions (new):

    ```Haskell liftCCLike :: (((a -> m b) -> m' c) -> m'' d) -> ((a -> Throws e m b) -> Throws e m' c) -> Throws e m'' d

    liftEmbedLike :: (forall a. m a -> Throws e n a) -> Throws e' m b -> Throws e n b

    liftHoistLike :: (forall a. m a -> n a) -> Throws e m b -> Throws e' n b ```

  • Documentation updates. (new)
  • Uploaded to [Hackage][]: http://hackage.haskell.org/package/tagged-exception-core-


http://hackage.haskell.org/package/exceptions "exceptions package on Hackage" [Hackage]: http://hackage.haskell.org/ "HackageDB (or just Hackage) is a collection of releases of Haskell packages." [mtl]: http://hackage.haskell.org/package/mtl "mtl package on Hackage" [transformers]: http://hackage.haskell.org/package/transformers "transformers package on Hackage"

Depends on 5 packages:
Used by 1 package:
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