haxl-2.0.1.1: A Haskell library for efficient, concurrent, and concise data access.

Safe HaskellNone
LanguageHaskell2010

Haxl.Core.Exception

Contents

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

MiddleException e => HaxlException (Maybe Stack) e 

Exception categories

data LogicError Source #

For errors in Haxl client code.

Constructors

Exception e => LogicError e 

Internal exceptions

newtype CriticalError Source #

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

Constructors

CriticalError Text 

newtype NonHaxlException Source #

Exceptions that are converted to HaxlException by asHaxlException. Typically these will be pure exceptions, e.g., the error function in pure code, or a pattern-match failure.

Constructors

NonHaxlException Text 

Logic exceptions

newtype NotFound Source #

Generic "something was not found" exception.

Constructors

NotFound Text 
Instances
Eq NotFound Source # 
Instance details

Defined in Haxl.Core.Exception

Show NotFound Source # 
Instance details

Defined in Haxl.Core.Exception

Exception NotFound Source # 
Instance details

Defined in Haxl.Core.Exception

Binary NotFound Source # 
Instance details

Defined in Haxl.Core.Exception

Methods

put :: NotFound -> Put #

get :: Get NotFound #

putList :: [NotFound] -> Put #

newtype EmptyList Source #

Generic "input list was empty" exception.

Constructors

EmptyList Text 

newtype JSONError Source #

Generic "Incorrect assumptions about JSON data" exception.

Constructors

JSONError Text 

newtype MonadFail Source #

Generic "fail was called" exception.

Constructors

MonadFail Text 

Transient exceptions

newtype FetchError Source #

Generic transient fetching exceptions.

Constructors

FetchError Text 

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 #

Minimal complete definition

eName

Methods

eName :: a -> String Source #