| Copyright | (c) Ross Paterson 2003 |
|---|---|
| License | BSD-style (see the LICENSE file in the distribution) |
| Maintainer | ross@soi.city.ac.uk |
| Stability | experimental |
| Portability | non-portable (multi-parameter type classes) |
| Safe Haskell | Safe-Inferred |
| Language | Haskell98 |
Control.Arrow.Internals
Description
Manipulation of composite arrow types, beyond the basic lifting and encapsulation provided with each arrow transformer.
The signatures are designed to be compatible with the proposed notation for arrows, cf. http://www.haskell.org/arrows/.
Synopsis
- class (ArrowState s a, Arrow a') => ArrowAddState s a a' | a -> a' where
- class (ArrowReader r a, Arrow a') => ArrowAddReader r a a' | a -> a' where
- liftReader :: a' e b -> a e b
- elimReader :: a e b -> a' (e, r) b
- class (ArrowWriter w a, Arrow a') => ArrowAddWriter w a a' | a -> a' where
- liftWriter :: a' e b -> a e b
- elimWriter :: a e b -> a' e (b, w)
- class (ArrowError ex a, Arrow a') => ArrowAddError ex a a' | a -> a' where
- class (ArrowCircuit a, Arrow a') => ArrowAddStream a a' | a -> a' where
- liftStream :: a' e b -> a e b
- elimStream :: a (e, b) c -> a' (e, Stream b) (Stream c)
Documentation
class (ArrowState s a, Arrow a') => ArrowAddState s a a' | a -> a' where Source #
Adding a StateArrow 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
runState encapsulation operator.
The methods of this class add and remove state transformers anywhere
in the stack. In the instance
instance Arrow a => ArrowAddState s (ArrowState s a) a
they are equivalent to lift and
runState respectively.
Instances are lifted through other transformers with
instance ArrowAddState s a a' =>
ArrowAddState s (FooArrow a) (FooArrow a')Methods
liftState :: a' e b -> a e b Source #
Lift a computation from an arrow to one with an added state.
Typical usage in arrow notation:
proc p -> ...
(|liftState cmd|)elimState :: a e b -> a' (e, s) (b, s) Source #
Elimination of a state transformer from a computation, exposing the initial and final states.
Typical usage in arrow notation:
proc p -> do
...
(result, final_state) <- (|elimState cmd|) init_stateInstances
class (ArrowReader r a, Arrow a') => ArrowAddReader r a a' | a -> a' where Source #
Adding a ReaderArrow 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
runReader encapsulation operator.
The methods of this class add and remove state transformers anywhere
in the stack. In the instance
instance Arrow a => ArrowAddReader r (ArrowReader r a) a
they are equivalent to lift and
runReader respectively.
Instances are lifted through other transformers with
instance ArrowAddReader r a a' =>
ArrowAddReader r (FooArrow a) (FooArrow a')Methods
liftReader :: a' e b -> a e b Source #
Lift a computation from an arrow to one with an added environment.
Typical usage in arrow notation:
proc p -> ...
(|liftReader cmd|)elimReader :: a e b -> a' (e, r) b Source #
Elimination of a state reader from a computation, taking a value for the state.
Typical usage in arrow notation:
proc p -> ...
(|elimReader cmd|) envInstances
class (ArrowWriter w a, Arrow a') => ArrowAddWriter w a a' | a -> a' where Source #
Adding a WriterArrow 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
runWriter encapsulation operator.
The methods of this class add and remove state transformers anywhere
in the stack. In the instance
instance Arrow a => ArrowAddWriter w (ArrowWriter w a) a
they are equivalent to lift and
runWriter respectively.
Instances are lifted through other transformers with
instance ArrowAddWriter w a a' =>
ArrowAddWriter w (FooArrow a) (FooArrow a')Methods
liftWriter :: a' e b -> a e b Source #
Lift a computation from an arrow to one with added output.
Typical usage in arrow notation:
proc p -> ...
(|liftWriter cmd|)elimWriter :: a e b -> a' e (b, w) Source #
Elimination of an output writer from a computation, providing the accumulated output.
Typical usage in arrow notation:
proc p -> do
...
(result, output) <- (|elimWriter cmd|)Instances
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.
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 -> handlerInstances
class (ArrowCircuit a, Arrow a') => ArrowAddStream a a' | a -> a' where Source #
Adding a StreamArrow 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
runStream encapsulation operator.
The methods of this class add and remove state transformers anywhere
in the stack. In the instance
instance Arrow a => ArrowAddStream (ArrowStream a) a
they are equivalent to lift and
runStream respectively.
Instances are lifted through other transformers with
instance ArrowAddStream a a' =>
ArrowAddStream (FooArrow a) (FooArrow a')Methods
liftStream :: a' e b -> a e b Source #
Lift a computation from an arrow to a stream processing one.
Typical usage in arrow notation:
proc p -> ...
(|liftStream cmd|)elimStream :: a (e, b) c -> a' (e, Stream b) (Stream c) Source #
Run a stream processor on a stream of inputs, obtaining a stream of outputs.
Typical usage in arrow notation:
proc p -> do
...
ys <- (|elimStream (\x -> ...)|) xsHere xs refers to the input stream and x to individual
elements of that stream. ys is bound to the output stream.
Instances
| (ArrowLoop a, ArrowApply a) => ArrowAddStream (Automaton a) a Source # | |
Defined in Control.Arrow.Transformer.Automaton Methods liftStream :: a e b -> Automaton a e b Source # elimStream :: Automaton a (e, b) c -> a (e, Stream b) (Stream c) Source # | |
| ArrowLoop a => ArrowAddStream (StreamArrow a) a Source # | |
Defined in Control.Arrow.Transformer.Stream Methods liftStream :: a e b -> StreamArrow a e b Source # elimStream :: StreamArrow a (e, b) c -> a (e, Stream b) (Stream c) Source # | |
| (ArrowAddStream a a', Applicative f) => ArrowAddStream (StaticArrow f a) (StaticArrow f a') Source # | |
Defined in Control.Arrow.Transformer.Static Methods liftStream :: StaticArrow f a' e b -> StaticArrow f a e b Source # elimStream :: StaticArrow f a (e, b) c -> StaticArrow f a' (e, Stream b) (Stream c) Source # | |