polysemy-zoo-0.7.0.1: Experimental, user-contributed effects and interpreters for polysemy

Safe HaskellNone
LanguageHaskell2010

Polysemy.ConstraintAbsorber.MonadCatch

Contents

Synopsis

Constraint Absorbers

absorbMonadThrow Source #

Arguments

:: Member (Error SomeException) r 
=> (MonadThrow (Sem r) => Sem r a)

A computation that requires an instance of MonadCatch or MonadThrow for Sem. This might be something with type MonadCatch e m => m a.

-> Sem r a 

Introduce a local MonadThrow constraint on Sem --- allowing it to interop nicely with exceptions

Since: 0.7.0.0

absorbMonadCatch Source #

Arguments

:: Member (Error SomeException) r 
=> (MonadCatch (Sem r) => Sem r a)

A computation that requires an instance of MonadCatch or MonadThrow for Sem. This might be something with type MonadCatch e m => m a.

-> Sem r a 

Introduce a local MonadCatch constraint on Sem --- allowing it to interop nicely with exceptions

Since: 0.7.0.0

run helper

runMonadCatch :: Exception e => (Maybe e -> e') -> Sem (Error SomeException ': (Error e' ': r)) a -> Sem r (Either e' a) Source #

Like runError but applies a given function from SomeException to some other type, typically something less opaque. e.g.: runErrorForMonadCatch C.displayException

Since: 0.7.0.0

Re-exports

class (Typeable e, Show e) => Exception e where #

Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

data MyException = ThisException | ThatException
    deriving Show

instance Exception MyException

The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException

In more complicated examples, you may wish to define a whole hierarchy of exceptions:

---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler

data SomeCompilerException = forall e . Exception e => SomeCompilerException e

instance Show SomeCompilerException where
    show (SomeCompilerException e) = show e

instance Exception SomeCompilerException

compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException

compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
    SomeCompilerException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler

data SomeFrontendException = forall e . Exception e => SomeFrontendException e

instance Show SomeFrontendException where
    show (SomeFrontendException e) = show e

instance Exception SomeFrontendException where
    toException = compilerExceptionToException
    fromException = compilerExceptionFromException

frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException

frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
    SomeFrontendException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception

data MismatchedParentheses = MismatchedParentheses
    deriving Show

instance Exception MismatchedParentheses where
    toException   = frontendExceptionToException
    fromException = frontendExceptionFromException

We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
*** Exception: MismatchedParentheses

Minimal complete definition

Nothing

Methods

toException :: e -> SomeException #

fromException :: SomeException -> Maybe e #

displayException :: e -> String #

Render this exception value in a human-friendly manner.

Default implementation: show.

Since: base-4.8.0.0

Instances
Exception AsyncCancelled 
Instance details

Defined in Control.Concurrent.Async

Exception ExceptionInLinkedThread 
Instance details

Defined in Control.Concurrent.Async

Exception Void

Since: base-4.8.0.0

Instance details

Defined in Data.Void

Exception PatternMatchFail

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecSelError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecConError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecUpdError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception NoMethodError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception TypeError

Since: base-4.9.0.0

Instance details

Defined in Control.Exception.Base

Exception NonTermination

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception NestedAtomically

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception BlockedIndefinitelyOnMVar

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception BlockedIndefinitelyOnSTM

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception Deadlock

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception AllocationLimitExceeded

Since: base-4.8.0.0

Instance details

Defined in GHC.IO.Exception

Exception CompactionFailed

Since: base-4.10.0.0

Instance details

Defined in GHC.IO.Exception

Exception AssertionFailed

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception SomeAsyncException

Since: base-4.7.0.0

Instance details

Defined in GHC.IO.Exception

Exception AsyncException

Since: base-4.7.0.0

Instance details

Defined in GHC.IO.Exception

Exception ArrayException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception FixIOException

Since: base-4.11.0.0

Instance details

Defined in GHC.IO.Exception

Exception ExitCode

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception IOException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception ErrorCall

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception

Exception ArithException

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception.Type

Exception SomeException

Since: base-3.0

Instance details

Defined in GHC.Exception.Type

Typeable e => Exception (WrappedExc e) 
Instance details

Defined in Polysemy.Error

Methods

toException :: WrappedExc e -> SomeException #

fromException :: SomeException -> Maybe (WrappedExc e) #

displayException :: WrappedExc e -> String #

data SomeException #

The SomeException type is the root of the exception type hierarchy. When an exception of type e is thrown, behind the scenes it is encapsulated in a SomeException.