Haxl.Core.Exception

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.

Documentation

data HaxlException

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

(Exception e, MiddleException e) => HaxlException (Maybe Stack) e

Instances

Show HaxlException

Methods

showsPrec :: Int -> HaxlException -> ShowS

show :: HaxlException -> String

showList :: [HaxlException] -> ShowS

ToJSON HaxlException

These need to be serializable to JSON to cross FFI boundaries.

Methods

toJSON :: HaxlException -> Value

toEncoding :: HaxlException -> Encoding

toJSONList :: [HaxlException] -> Value

toEncodingList :: [HaxlException] -> Encoding

Exception HaxlException

Methods

toException :: HaxlException -> SomeException

fromException :: SomeException -> Maybe HaxlException

displayException :: HaxlException -> String

Exception categories

data InternalError

For errors in Haxl core code.

Constructors

Exception e => InternalError e

Instances

Show InternalError

Methods

showsPrec :: Int -> InternalError -> ShowS

show :: InternalError -> String

showList :: [InternalError] -> ShowS

Exception InternalError

Methods

toException :: InternalError -> SomeException

fromException :: SomeException -> Maybe InternalError

displayException :: InternalError -> String

MiddleException InternalError

Methods

eName :: InternalError -> String

internalErrorToException :: Exception e => e -> SomeException

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

data LogicError

For errors in Haxl client code.

Constructors

Exception e => LogicError e

Instances

Show LogicError

Methods

showsPrec :: Int -> LogicError -> ShowS

show :: LogicError -> String

showList :: [LogicError] -> ShowS

Exception LogicError

Methods

toException :: LogicError -> SomeException

fromException :: SomeException -> Maybe LogicError

displayException :: LogicError -> String

MiddleException LogicError

Methods

eName :: LogicError -> String

logicErrorToException :: Exception e => e -> SomeException

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

data LogicBug

Constructors

Exception e => LogicBug e

Instances

Show LogicBug

Methods

showsPrec :: Int -> LogicBug -> ShowS

show :: LogicBug -> String

showList :: [LogicBug] -> ShowS

Exception LogicBug

Methods

toException :: LogicBug -> SomeException

fromException :: SomeException -> Maybe LogicBug

displayException :: LogicBug -> String

MiddleException LogicBug

Methods

eName :: LogicBug -> String

logicBugToException :: Exception e => e -> SomeException

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

data TransientError

For transient failures.

Constructors

Exception e => TransientError e

Instances

Show TransientError

Methods

showsPrec :: Int -> TransientError -> ShowS

show :: TransientError -> String

showList :: [TransientError] -> ShowS

Exception TransientError

Methods

toException :: TransientError -> SomeException

fromException :: SomeException -> Maybe TransientError

displayException :: TransientError -> String

MiddleException TransientError

Methods

eName :: TransientError -> String

transientErrorToException :: Exception e => e -> SomeException

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

Internal exceptions

newtype CriticalError

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

Constructors

CriticalError Text

Instances

Eq CriticalError

Methods

(==) :: CriticalError -> CriticalError -> Bool

(/=) :: CriticalError -> CriticalError -> Bool

Show CriticalError

Methods

showsPrec :: Int -> CriticalError -> ShowS

show :: CriticalError -> String

showList :: [CriticalError] -> ShowS

Exception CriticalError

Methods

toException :: CriticalError -> SomeException

fromException :: SomeException -> Maybe CriticalError

displayException :: CriticalError -> String

Binary CriticalError

Methods

put :: CriticalError -> Put

get :: Get CriticalError

putList :: [CriticalError] -> Put

newtype DataSourceError

A data source did something wrong

Constructors

DataSourceError Text

Instances

Eq DataSourceError

Methods

(==) :: DataSourceError -> DataSourceError -> Bool

(/=) :: DataSourceError -> DataSourceError -> Bool

Show DataSourceError

Methods

showsPrec :: Int -> DataSourceError -> ShowS

show :: DataSourceError -> String

showList :: [DataSourceError] -> ShowS

Exception DataSourceError

Methods

toException :: DataSourceError -> SomeException

fromException :: SomeException -> Maybe DataSourceError

displayException :: DataSourceError -> String

Logic exceptions

newtype NotFound

Generic "something was not found" exception.

Constructors

NotFound Text

Instances

Eq NotFound

Methods

(==) :: NotFound -> NotFound -> Bool

(/=) :: NotFound -> NotFound -> Bool

Show NotFound

Methods

showsPrec :: Int -> NotFound -> ShowS

show :: NotFound -> String

showList :: [NotFound] -> ShowS

Exception NotFound

Methods

toException :: NotFound -> SomeException

fromException :: SomeException -> Maybe NotFound

displayException :: NotFound -> String

Binary NotFound

Methods

put :: NotFound -> Put

get :: Get NotFound

putList :: [NotFound] -> Put

newtype UnexpectedType

Generic "something had the wrong type" exception.

Constructors

UnexpectedType Text

Instances

Eq UnexpectedType

Methods

(==) :: UnexpectedType -> UnexpectedType -> Bool

(/=) :: UnexpectedType -> UnexpectedType -> Bool

Show UnexpectedType

Methods

showsPrec :: Int -> UnexpectedType -> ShowS

show :: UnexpectedType -> String

showList :: [UnexpectedType] -> ShowS

Exception UnexpectedType

Methods

toException :: UnexpectedType -> SomeException

fromException :: SomeException -> Maybe UnexpectedType

displayException :: UnexpectedType -> String

newtype EmptyList

Generic "input list was empty" exception.

Constructors

EmptyList Text

Instances

Eq EmptyList

Methods

(==) :: EmptyList -> EmptyList -> Bool

(/=) :: EmptyList -> EmptyList -> Bool

Show EmptyList

Methods

showsPrec :: Int -> EmptyList -> ShowS

show :: EmptyList -> String

showList :: [EmptyList] -> ShowS

Exception EmptyList

Methods

toException :: EmptyList -> SomeException

fromException :: SomeException -> Maybe EmptyList

displayException :: EmptyList -> String

newtype JSONError

Generic "Incorrect assumptions about JSON data" exception.

Constructors

JSONError Text

Instances

Eq JSONError

Methods

(==) :: JSONError -> JSONError -> Bool

(/=) :: JSONError -> JSONError -> Bool

Show JSONError

Methods

showsPrec :: Int -> JSONError -> ShowS

show :: JSONError -> String

showList :: [JSONError] -> ShowS

Exception JSONError

Methods

toException :: JSONError -> SomeException

fromException :: SomeException -> Maybe JSONError

displayException :: JSONError -> String

newtype InvalidParameter

Generic "passing some invalid parameter" exception.

Constructors

InvalidParameter Text

Instances

Eq InvalidParameter

Methods

(==) :: InvalidParameter -> InvalidParameter -> Bool

(/=) :: InvalidParameter -> InvalidParameter -> Bool

Show InvalidParameter

Methods

showsPrec :: Int -> InvalidParameter -> ShowS

show :: InvalidParameter -> String

showList :: [InvalidParameter] -> ShowS

Exception InvalidParameter

Methods

toException :: InvalidParameter -> SomeException

fromException :: SomeException -> Maybe InvalidParameter

displayException :: InvalidParameter -> String

newtype MonadFail

Generic "fail was called" exception.

Constructors

MonadFail Text

Instances

Eq MonadFail

Methods

(==) :: MonadFail -> MonadFail -> Bool

(/=) :: MonadFail -> MonadFail -> Bool

Show MonadFail

Methods

showsPrec :: Int -> MonadFail -> ShowS

show :: MonadFail -> String

showList :: [MonadFail] -> ShowS

Exception MonadFail

Methods

toException :: MonadFail -> SomeException

fromException :: SomeException -> Maybe MonadFail

displayException :: MonadFail -> String

Transient exceptions

newtype FetchError

Generic transient fetching exceptions.

Constructors

FetchError Text

Instances

Eq FetchError

Methods

(==) :: FetchError -> FetchError -> Bool

(/=) :: FetchError -> FetchError -> Bool

Show FetchError

Methods

showsPrec :: Int -> FetchError -> ShowS

show :: FetchError -> String

showList :: [FetchError] -> ShowS

Exception FetchError

Methods

toException :: FetchError -> SomeException

fromException :: SomeException -> Maybe FetchError

displayException :: FetchError -> String

Exception utilities

asHaxlException :: SomeException -> HaxlException

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

class Exception a => MiddleException a where

Minimal complete definition

eName

Methods

eName :: a -> String

Instances

MiddleException LogicBug

Methods

eName :: LogicBug -> String

MiddleException LogicError

Methods

eName :: LogicError -> String

MiddleException InternalError

Methods

eName :: InternalError -> String

MiddleException TransientError

Methods

eName :: TransientError -> String