{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE UnicodeSyntax #-}

{- |
Description : Projections into the Haskell exception hierarchy
Copyright   : Copyright 2022 Shea Levy.
License     : Apache-2.0
Maintainer  : shea@shealevy.com

Provides 'Exceptable' for error types which can be projected into
the Haskell exception hierarchy.
-}
module Data.Exceptable where

import Control.Exception
import Data.Typeable
import Data.Void

-- | Types which can be projected into the Haskell exception hierarchy
class Exceptable e where
  toSomeException ∷ e → SomeException

instance Exceptable SomeException where
  toSomeException :: SomeException -> SomeException
toSomeException = forall a. a -> a
id

instance Exceptable Void where
  toSomeException :: Void -> SomeException
toSomeException = forall a. Void -> a
absurd

-- | An 'Exception' representing a failure in the 'Either' monad.
newtype EitherException e = EitherException e deriving stock (Int -> EitherException e -> ShowS
forall e. Show e => Int -> EitherException e -> ShowS
forall e. Show e => [EitherException e] -> ShowS
forall e. Show e => EitherException e -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [EitherException e] -> ShowS
$cshowList :: forall e. Show e => [EitherException e] -> ShowS
show :: EitherException e -> String
$cshow :: forall e. Show e => EitherException e -> String
showsPrec :: Int -> EitherException e -> ShowS
$cshowsPrec :: forall e. Show e => Int -> EitherException e -> ShowS
Show)

instance (Show e, Typeable e) ⇒ Exception (EitherException e)

instance (Show e, Typeable e) ⇒ Exceptable (EitherException e) where
  toSomeException :: EitherException e -> SomeException
toSomeException = forall e. Exception e => e -> SomeException
toException

-- | An 'Exception' representing the 'Nothing' case in a 'Maybe' monad.
data NothingException = NothingException deriving (Int -> NothingException -> ShowS
[NothingException] -> ShowS
NothingException -> String
forall a.
(Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
showList :: [NothingException] -> ShowS
$cshowList :: [NothingException] -> ShowS
show :: NothingException -> String
$cshow :: NothingException -> String
showsPrec :: Int -> NothingException -> ShowS
$cshowsPrec :: Int -> NothingException -> ShowS
Show)

instance Exception NothingException

instance Exceptable e ⇒ Exceptable (Maybe e) where
  toSomeException :: Maybe e -> SomeException
toSomeException (Just e
e) = forall e. Exceptable e => e -> SomeException
toSomeException e
e
  toSomeException Maybe e
Nothing = forall e. Exception e => e -> SomeException
toException NothingException
NothingException

instance (Show e, Typeable e, Exceptable e') ⇒ Exceptable (Either e e') where
  toSomeException :: Either e e' -> SomeException
toSomeException (Left e
e) = forall e. Exception e => e -> SomeException
toException forall a b. (a -> b) -> a -> b
$ forall e. e -> EitherException e
EitherException e
e
  toSomeException (Right e'
e) = forall e. Exceptable e => e -> SomeException
toSomeException e'
e

instance Exceptable e ⇒ Exceptable (e, s) where
  toSomeException :: (e, s) -> SomeException
toSomeException (e
e, s
_) = forall e. Exceptable e => e -> SomeException
toSomeException e
e

instance Exceptable e ⇒ Exceptable (e, s, w) where
  toSomeException :: (e, s, w) -> SomeException
toSomeException (e
e, s
_, w
_) = forall e. Exceptable e => e -> SomeException
toSomeException e
e