Copyright | (c) 2015 Schell Scivally |
---|---|
License | MIT |
Maintainer | Schell Scivally <schell.scivally@synapsegroup.com> |
Safe Haskell | None |
Language | Haskell2010 |
Using splines we can easily create continuous value streams from multiple piecewise event streams. A spline is a monadic layer on top of event streams which are only continuous over a certain domain. The idea is that we use do notation to "run an event stream" from which we will consume produced values. Once the event stream inhibits the computation completes and returns a result value. That result value is then used to determine the next spline in the sequence.
A spline can be converted back into a value stream using execSpline
or
execSplineT
. This allows us to build long, complex, sequential behaviors
using familiar notation.
- type Spline a b c = SplineT a b Identity c
- newtype SplineT a b m c = SplineT {
- runSplineT :: a -> m (Either c (b, SplineT a b m c))
- scanSpline :: (Applicative m, Monad m) => SplineT a b m c -> b -> [a] -> m [b]
- outputStream :: (Applicative m, Monad m) => SplineT a b m c -> b -> VarT m a b
- step :: (Applicative m, Monad m) => b -> SplineT a b m ()
- fromEvent :: (Applicative m, Monad m) => VarT m a (Event b) -> SplineT a (Event b) m b
- untilEvent :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m (b, c)
- untilEvent_ :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m b
- _untilEvent :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m c
- _untilEvent_ :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m ()
- race :: (Applicative m, Monad m) => (a -> b -> c) -> SplineT i a m d -> SplineT i b m e -> SplineT i c m (Either d e)
- raceMany :: (Applicative m, Monad m, Monoid b) => [SplineT a b m c] -> SplineT a b m c
- merge :: (Applicative m, Monad m) => (b -> b -> b) -> SplineT a b m c -> SplineT a b m d -> SplineT a b m (c, d)
- capture :: (Applicative m, Monad m) => SplineT a b m c -> SplineT a b m (Maybe b, c)
- mapOutput :: (Applicative m, Monad m) => VarT m a (b -> t) -> SplineT a b m c -> SplineT a t m c
- adjustInput :: (Applicative m, Monad m) => VarT m a (a -> r) -> SplineT r b m c -> SplineT a b m c
Spline
type Spline a b c = SplineT a b Identity c Source
A SplineT monad parameterized with Identity that takes input of type a
,
output of type b
and a result value of type c
.
Spline Transformer
newtype SplineT a b m c Source
SplineT
shares all the types of VarT
and adds a result value. Its
monad, input and output types (m
, a
and b
, respectively) reflect the
underlying VarT
. A spline adds a result type which represents the monadic
computation's result value.
Much like the State monad it has an "internal state" and an eventual
result value, where the internal state is the output value. The result
value is used only in determining the next spline to sequence.
newtype SplineT a b m c = SplineT { unSplineT :: VarT m a (Either b c) }
SplineT | |
|
MonadTrans (SplineT a b) Source | A spline is a transformer by using |
(Applicative m, Monad m) => Monad (SplineT a b m) Source | A spline responds to bind by running until it concludes in a value, then uses that value to run the next spline. |
(Applicative m, Monad m) => Functor (SplineT a b m) Source | A spline is a functor by applying the function to the result of the spline. |
(Applicative m, Monad m) => Applicative (SplineT a b m) Source | |
(Applicative m, Monad m, MonadIO m) => MonadIO (SplineT a b m) Source | A spline can do IO if its underlying monad has a MonadIO instance. It takes the result of the IO action as its immediate return value. |
Running and streaming
scanSpline :: (Applicative m, Monad m) => SplineT a b m c -> b -> [a] -> m [b] Source
Run the spline over the input values, gathering the output values in a list.
outputStream :: (Applicative m, Monad m) => SplineT a b m c -> b -> VarT m a b Source
Evaluates a spline into a value stream of its output type.
Combinators
step :: (Applicative m, Monad m) => b -> SplineT a b m () Source
Produce the argument as an output value exactly once.
fromEvent :: (Applicative m, Monad m) => VarT m a (Event b) -> SplineT a (Event b) m b Source
Create a spline from an event stream.
untilEvent :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m (b, c) Source
Create a spline from a value stream and an event stream. The spline uses the value stream as its output value. The spline will run until the event stream produces a value, at that point the last output value and the event value are tupled and returned as the spline's result value.
untilEvent_ :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m b Source
A variant of untilEvent
that only results in the left result,
discarding the right result.
_untilEvent :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m c Source
A variant of untilEvent
that only results in the right result,
discarding the left result.
_untilEvent_ :: (Applicative m, Monad m) => VarT m a b -> VarT m a (Event c) -> SplineT a b m () Source
race :: (Applicative m, Monad m) => (a -> b -> c) -> SplineT i a m d -> SplineT i b m e -> SplineT i c m (Either d e) Source
Run two splines in parallel, combining their output. Return the result of the spline that concludes first. If they conclude at the same time the result is taken from the left spline.
merge :: (Applicative m, Monad m) => (b -> b -> b) -> SplineT a b m c -> SplineT a b m d -> SplineT a b m (c, d) Source
Run two splines in parallel, combining their output. Once both splines have concluded, return the results of each in a tuple.
capture :: (Applicative m, Monad m) => SplineT a b m c -> SplineT a b m (Maybe b, c) Source
Capture the spline's last output value and tuple it with the spline's result. This is helpful when you want to sample the last output value in order to determine the next spline to sequence.
mapOutput :: (Applicative m, Monad m) => VarT m a (b -> t) -> SplineT a b m c -> SplineT a t m c Source
Map the output value of a spline.
adjustInput :: (Applicative m, Monad m) => VarT m a (a -> r) -> SplineT r b m c -> SplineT a b m c Source
Map the input value of a spline.