Copyright	(c) Ross Paterson 2003
License	BSD-style (see the LICENSE file in the distribution)
Maintainer	R.Paterson@city.ac.uk
Stability	experimental
Portability	non-portable (multi-parameter type classes)
Safe Haskell	Safe
Language	Haskell98

Control.Arrow.Transformer.Error

Description

An arrow transformer that adds error handling.

TODO: the operations here are inconsistent with other arrow transformers.

Synopsis

Documentation

newtype ErrorArrow ex a b c Source #

An arrow that augments an existing arrow with possible errors. The ArrowError class contains methods for raising and handling these errors.

Constructors

ErrorArrow (a b (Either ex c))

Instances

ArrowChoice a => ArrowError ex (ErrorArrow ex a) Source #
Methods raise :: ErrorArrow ex a ex b Source # handle :: ErrorArrow ex a e b -> ErrorArrow ex a (e, ex) b -> ErrorArrow ex a e b Source # tryInUnless :: ErrorArrow ex a e b -> ErrorArrow ex a (e, b) c -> ErrorArrow ex a (e, ex) c -> ErrorArrow ex a e c Source # newError :: ErrorArrow ex a e b -> ErrorArrow ex a e (Either ex b) Source #
(ArrowWriter w a, ArrowChoice a) => ArrowWriter w (ErrorArrow ex a) Source #
Methods write :: ErrorArrow ex a w () Source # newWriter :: ErrorArrow ex a e b -> ErrorArrow ex a e (b, w) Source #
(ArrowState s a, ArrowChoice a) => ArrowState s (ErrorArrow ex a) Source #
Methods fetch :: ErrorArrow ex a e s Source # store :: ErrorArrow ex a s () Source #
(ArrowReader r a, ArrowChoice a) => ArrowReader r (ErrorArrow ex a) Source #
Methods readState :: ErrorArrow ex a b r Source # newReader :: ErrorArrow ex a e b -> ErrorArrow ex a (e, r) b Source #
ArrowChoice a => ArrowAddError ex (ErrorArrow ex a) a Source #
Methods liftError :: a e b -> ErrorArrow ex a e b Source # elimError :: ErrorArrow ex a e b -> a (e, ex) b -> a e b Source #
(ArrowAddWriter w a a', ArrowChoice a, ArrowChoice a') => ArrowAddWriter w (ErrorArrow ex a) (ErrorArrow ex a') Source #
Methods liftWriter :: ErrorArrow ex a' e b -> ErrorArrow ex a e b Source # elimWriter :: ErrorArrow ex a e b -> ErrorArrow ex a' e (b, w) Source #
(ArrowAddReader r a a', ArrowChoice a, ArrowChoice a') => ArrowAddReader r (ErrorArrow ex a) (ErrorArrow ex a') Source #
Methods liftReader :: ErrorArrow ex a' e b -> ErrorArrow ex a e b Source # elimReader :: ErrorArrow ex a e b -> ErrorArrow ex a' (e, r) b Source #
(ArrowAddState s a a', ArrowChoice a, ArrowChoice a') => ArrowAddState s (ErrorArrow ex a) (ErrorArrow ex a') Source #
Methods liftState :: ErrorArrow ex a' e b -> ErrorArrow ex a e b Source # elimState :: ErrorArrow ex a e b -> ErrorArrow ex a' (e, s) (b, s) Source #
ArrowChoice a => ArrowTransformer (ErrorArrow ex) a Source #
Methods lift :: a b c -> ErrorArrow ex a b c Source #
ArrowChoice a => Category * (ErrorArrow ex a) Source #
Methods id :: cat a a # (.) :: cat b c -> cat a b -> cat a c #
ArrowChoice a => Arrow (ErrorArrow ex a) Source #
Methods arr :: (b -> c) -> ErrorArrow ex a b c # first :: ErrorArrow ex a b c -> ErrorArrow ex a (b, d) (c, d) # second :: ErrorArrow ex a b c -> ErrorArrow ex a (d, b) (d, c) # (***) :: ErrorArrow ex a b c -> ErrorArrow ex a b' c' -> ErrorArrow ex a (b, b') (c, c') # (&&&) :: ErrorArrow ex a b c -> ErrorArrow ex a b c' -> ErrorArrow ex a b (c, c') #
(Monoid ex, ArrowChoice a) => ArrowZero (ErrorArrow ex a) Source #
Methods zeroArrow :: ErrorArrow ex a b c #
(Monoid ex, ArrowChoice a) => ArrowPlus (ErrorArrow ex a) Source #
Methods (<+>) :: ErrorArrow ex a b c -> ErrorArrow ex a b c -> ErrorArrow ex a b c #
ArrowChoice a => ArrowChoice (ErrorArrow ex a) Source #
Methods left :: ErrorArrow ex a b c -> ErrorArrow ex a (Either b d) (Either c d) # right :: ErrorArrow ex a b c -> ErrorArrow ex a (Either d b) (Either d c) # (+++) :: ErrorArrow ex a b c -> ErrorArrow ex a b' c' -> ErrorArrow ex a (Either b b') (Either c c') # (\|\|\|) :: ErrorArrow ex a b d -> ErrorArrow ex a c d -> ErrorArrow ex a (Either b c) d #
(ArrowChoice a, ArrowApply a) => ArrowApply (ErrorArrow ex a) Source #
Methods app :: ErrorArrow ex a (ErrorArrow ex a b c, b) c #
(ArrowChoice a, ArrowLoop a) => ArrowLoop (ErrorArrow ex a) Source #
Methods loop :: ErrorArrow ex a (b, d) (c, d) -> ErrorArrow ex a b c #
ArrowChoice a => Functor (ErrorArrow ex a b) Source #
Methods fmap :: (a -> b) -> ErrorArrow ex a b a -> ErrorArrow ex a b b # (<$) :: a -> ErrorArrow ex a b b -> ErrorArrow ex a b a #
ArrowChoice a => Applicative (ErrorArrow ex a b) Source #
Methods pure :: a -> ErrorArrow ex a b a # (<>) :: ErrorArrow ex a b (a -> b) -> ErrorArrow ex a b a -> ErrorArrow ex a b b # liftA2 :: (a -> b -> c) -> ErrorArrow ex a b a -> ErrorArrow ex a b b -> ErrorArrow ex a b c # (>) :: ErrorArrow ex a b a -> ErrorArrow ex a b b -> ErrorArrow ex a b b # (<*) :: ErrorArrow ex a b a -> ErrorArrow ex a b b -> ErrorArrow ex a b a #
(Monoid ex, ArrowChoice a) => Alternative (ErrorArrow ex a b) Source #
Methods empty :: ErrorArrow ex a b a # (<\|>) :: ErrorArrow ex a b a -> ErrorArrow ex a b a -> ErrorArrow ex a b a # some :: ErrorArrow ex a b a -> ErrorArrow ex a b [a] # many :: ErrorArrow ex a b a -> ErrorArrow ex a b [a] #
(Monoid ex, ArrowChoice a) => Semigroup (ErrorArrow ex a b c) Source #
Methods (<>) :: ErrorArrow ex a b c -> ErrorArrow ex a b c -> ErrorArrow ex a b c # sconcat :: NonEmpty (ErrorArrow ex a b c) -> ErrorArrow ex a b c # stimes :: Integral b => b -> ErrorArrow ex a b c -> ErrorArrow ex a b c #
(Monoid ex, ArrowChoice a) => Monoid (ErrorArrow ex a b c) Source #
Methods mempty :: ErrorArrow ex a b c # mappend :: ErrorArrow ex a b c -> ErrorArrow ex a b c -> ErrorArrow ex a b c # mconcat :: [ErrorArrow ex a b c] -> ErrorArrow ex a b c #

runError Source #

Arguments

:: ArrowChoice a
=> ErrorArrow ex a e b	computation that may raise errors
-> a (e, ex) b	computation to handle errors
-> a e b

Encapsulate an error-raising computation, by completely handling any errors.

Typical usage in arrow notation:

   proc p -> ...
       body `runError` \ex -> handler

class (ArrowError ex a, Arrow a') => ArrowAddError ex a a' | a -> a' where Source #

Adding a ErrorArrow to an arrow type, but not necessarily as the outer arrow transformer.

Typically a composite arrow type is built by applying a series of arrow transformer to a base arrow (usually either a function arrow or a Kleisli arrow. One can add a transformer to the top of this stack using the lift method of the ArrowTransformer class, or remove a state transformer from the top of the stack using the runError encapsulation operator. The methods of this class add and remove state transformers anywhere in the stack. In the instance

   instance Arrow a => ArrowAddError ex (ArrowError ex a) a

they are equivalent to lift and runError respectively. Instances are lifted through other transformers with

   instance ArrowAddError ex a a' =>
       ArrowAddError ex (FooArrow a) (FooArrow a')

This could be combined with handle, since the resulting arrow is always the arrow of the handler. Separating them has the advantage of consistency with the other arrows, and might give more helpful type error messages.

Minimal complete definition

liftError, elimError

Methods

liftError :: a' e b -> a e b Source #

Lift a computation from an arrow to one with error handling.

Typical usage in arrow notation:

   proc p -> ...
       (|liftError cmd|)

elimError :: a e b -> a' (e, ex) b -> a' e b Source #

Elimination of errors from a computation, by completely handling any errors.

Typical usage in arrow notation:

   proc p -> ...
       body `elimError` \ex -> handler

Instances

ArrowChoice a => ArrowAddError ex (ErrorArrow ex a) a Source #
Methods liftError :: a e b -> ErrorArrow ex a e b Source # elimError :: ErrorArrow ex a e b -> a (e, ex) b -> a e b Source #
ArrowAddError ex a a' => ArrowAddError ex (ReaderArrow r a) (ReaderArrow r a') Source #
Methods liftError :: ReaderArrow r a' e b -> ReaderArrow r a e b Source # elimError :: ReaderArrow r a e b -> ReaderArrow r a' (e, ex) b -> ReaderArrow r a' e b Source #
ArrowAddError ex a a' => ArrowAddError ex (StateArrow s a) (StateArrow s a') Source #
Methods liftError :: StateArrow s a' e b -> StateArrow s a e b Source # elimError :: StateArrow s a e b -> StateArrow s a' (e, ex) b -> StateArrow s a' e b Source #
(ArrowAddError ex a a', Applicative f) => ArrowAddError ex (StaticArrow f a) (StaticArrow f a') Source #
Methods liftError :: StaticArrow f a' e b -> StaticArrow f a e b Source # elimError :: StaticArrow f a e b -> StaticArrow f a' (e, ex) b -> StaticArrow f a' e b Source #
(ArrowAddError ex a a', Monoid w) => ArrowAddError ex (WriterArrow w a) (WriterArrow w a') Source #
Methods liftError :: WriterArrow w a' e b -> WriterArrow w a e b Source # elimError :: WriterArrow w a e b -> WriterArrow w a' (e, ex) b -> WriterArrow w a' e b Source #