Safe Haskell	None
Language	Haskell2010

Haxl.Core.Exception

Contents

Exception categories
Exception utilities

Description

An exception hierarchy that can be used with the Haxl monad.

The Haxl framework may throw exceptions from this hierarchy: for example, a misbehaving data source causes dataFetch to throw a DataSourceError. The combinator withDefault from Haxl.Core.Prelude uses this hierarchy to provide default values for expressions that raise TransientError or LogicError exceptions.

You are under no obligations to use this hierarchy for your own exceptions, but you might find it useful nonetheless; for withDefault to be useful, for example, you'll want your exceptions to be children of LogicError or TransientError as appropriate.

Most users should import Haxl.Core instead of importing this module directly.

Synopsis

Documentation

data HaxlException Source

We have a 3-tiered hierarchy of exceptions, with HaxlException at the top, and all Haxl exceptions as children of this. Users should never deal directly with HaxlExceptions.

The main types of exceptions are:

InternalError: Something is wrong with Haxl core.
LogicBug: Something is wrong with Haxl client code.
LogicError: Things that really should be return values, e.g. NotFound.
TransientError: Something is temporarily failing (usually in a fetch).

These are not meant to be thrown (but likely be caught). Thrown exceptions should be a subclass of one of these. There are some generic leaf exceptions defined below this, such as FetchError (generic transient failure) or CriticalError (internal failure).

Constructors

forall e . MiddleException e => HaxlException (Maybe Stack) e

Instances

Show HaxlException Source
ToJSON HaxlException Source	These need to be serializable to JSON to cross FFI boundaries.
Exception HaxlException Source

Exception categories

data InternalError Source

For errors in Haxl core code.

Constructors

forall e . Exception e => InternalError e

Instances

Show InternalError Source
Exception InternalError Source
MiddleException InternalError Source

internalErrorToException :: Exception e => e -> SomeException Source

internalErrorFromException :: Exception e => SomeException -> Maybe e Source

data LogicError Source

For errors in Haxl client code.

Constructors

forall e . Exception e => LogicError e

Instances

Show LogicError Source
Exception LogicError Source
MiddleException LogicError Source

logicErrorToException :: Exception e => e -> SomeException Source

logicErrorFromException :: Exception e => SomeException -> Maybe e Source

data LogicBug Source

Constructors

forall e . Exception e => LogicBug e

Instances

Show LogicBug Source
Exception LogicBug Source
MiddleException LogicBug Source

logicBugToException :: Exception e => e -> SomeException Source

logicBugFromException :: Exception e => SomeException -> Maybe e Source

data TransientError Source

For transient failures.

Constructors

forall e . Exception e => TransientError e

Instances

Show TransientError Source
Exception TransientError Source
MiddleException TransientError Source

transientErrorToException :: Exception e => e -> SomeException Source

transientErrorFromException :: Exception e => SomeException -> Maybe e Source

Internal exceptions

newtype CriticalError Source

Generic "critical" exception. Something internal is borked. Panic.

Constructors

CriticalError Text

Instances

Eq CriticalError Source
Show CriticalError Source
Exception CriticalError Source
Binary CriticalError Source

newtype DataSourceError Source

A data source did something wrong

Constructors

DataSourceError Text

Instances

Eq DataSourceError Source
Show DataSourceError Source
Exception DataSourceError Source

Logic exceptions

newtype NotFound Source

Generic "something was not found" exception.

Constructors

NotFound Text

Instances

Eq NotFound Source
Show NotFound Source
Exception NotFound Source
Binary NotFound Source

newtype UnexpectedType Source

Generic "something had the wrong type" exception.

Constructors

UnexpectedType Text

Instances

Eq UnexpectedType Source
Show UnexpectedType Source
Exception UnexpectedType Source

newtype EmptyList Source

Generic "input list was empty" exception.

Constructors

EmptyList Text

Instances

Eq EmptyList Source
Show EmptyList Source
Exception EmptyList Source

newtype JSONError Source

Generic "Incorrect assumptions about JSON data" exception.

Constructors

JSONError Text

Instances

Eq JSONError Source
Show JSONError Source
Exception JSONError Source

newtype InvalidParameter Source

Generic "passing some invalid parameter" exception.

Constructors

InvalidParameter Text

Instances

Eq InvalidParameter Source
Show InvalidParameter Source
Exception InvalidParameter Source

newtype MonadFail Source

Generic "fail was called" exception.

Constructors

MonadFail Text

Instances

Eq MonadFail Source
Show MonadFail Source
Exception MonadFail Source

Transient exceptions

newtype FetchError Source

Generic transient fetching exceptions.

Constructors

FetchError Text

Instances

Eq FetchError Source
Show FetchError Source
Exception FetchError Source

Exception utilities

asHaxlException :: SomeException -> HaxlException Source

Converts all exceptions that are not derived from HaxlException into NonHaxlException, using show.

class Exception a => MiddleException a where Source

Methods

eName :: a -> String Source

Instances

MiddleException LogicBug Source
MiddleException LogicError Source
MiddleException InternalError Source
MiddleException TransientError Source