Copyright | (c) 2015 Schell Scivally |
---|---|
License | MIT |
Maintainer | Schell Scivally <schell.scivally@synapsegroup.com> |
Safe Haskell | None |
Language | Haskell2010 |
Value streams represent values that change over a given domain.
A stream takes some input (the domain e.g. time, place, etc) and when
sampled using runVarT
- produces a value and a new value stream. This
pattern is known as an automaton. varying
uses this pattern as its base
type with the additon of a monadic computation to create locally stateful
signals that change over some domain.
- type Var a b = VarT Identity a b
- newtype VarT m a b = VarT {}
- done :: (Applicative m, Monad m) => b -> VarT m a b
- var :: Applicative m => (a -> b) -> VarT m a b
- varM :: Monad m => (a -> m b) -> VarT m a b
- mkState :: Monad m => (a -> s -> (b, s)) -> s -> VarT m a b
- (<~) :: (Monad m, Applicative m) => VarT m b c -> VarT m a b -> VarT m a c
- (~>) :: (Monad m, Applicative m) => VarT m a b -> VarT m b c -> VarT m a c
- (<<<) :: Category k cat => cat b c -> cat a b -> cat a c
- (>>>) :: Category k cat => cat a b -> cat b c -> cat a c
- delay :: (Monad m, Applicative m) => b -> VarT m a b -> VarT m a b
- accumulate :: (Monad m, Applicative m) => (c -> b -> c) -> c -> VarT m b c
- scanVar :: (Applicative m, Monad m) => VarT m a b -> [a] -> m ([b], VarT m a b)
- stepMany :: (Monad m, Functor m) => VarT m a b -> [a] -> a -> m (b, VarT m a b)
- vtrace :: (Applicative a, Show b) => VarT a b b
- vstrace :: (Applicative a, Show b) => String -> VarT a b b
- vftrace :: Applicative a => (b -> String) -> VarT a b b
Documentation
type Var a b = VarT Identity a b Source
A value stream parameterized with Identity that takes input of type a
and gives output of type b
. This is the pure, effect-free version of
VarT
.
A value stream is a structure that contains a value that changes over some
input. It's a kind of Mealy machine (an automaton) with effects. Using
runVarT
with an input value of type a
yields a "step", which is a value
of type b
and a new VarT
for yielding the next value.
VarT | Given an input value, return a computation that effectfully produces an output value and a new stream for producing the next sample. |
(Applicative m, Monad m) => Category * (VarT m) Source | A very simple category instance. id = var id f . g = g >>> f or f . g = f <<< g It is preferable for consistency (and readability) to use 'plug left' ( |
(Applicative m, Monad m) => Arrow (VarT m) Source | Streams are arrows, which means you can use proc notation. v = proc a -> do ex <- intEventVar -< () ey <- anotherIntEventVar -< () returnA -< (+) <$> ex <*> ey which is equivalent to v = (\ex ey -> (+) <$> ex <*> ey) <$> intEventVar <*> anotherIntEventVar |
(Applicative m, Monad m) => Functor (VarT m b) Source | You can transform the sample value of any stream: fmap (*3) $ accumulate (+) 0 Will sum input values and then multiply the sum by 3. |
(Applicative m, Monad m) => Applicative (VarT m a) Source | Streams are applicative. (,) <$> pure True <*> var "Applicative" |
(Applicative m, Monad m, Floating b) => Floating (VarT m a b) Source | Streams can be written as floats. let v = pi >>> accumulate (*) 0.0 which will attempt (and succeed) to multiply pi by zero every step. |
(Applicative m, Monad m, Fractional b) => Fractional (VarT m a b) Source | Streams can be written as fractionals. let v = 2.5 >>> accumulate (+) 0 which will add 2.5 each step. |
(Applicative m, Monad m, Num b) => Num (VarT m a b) Source | Streams can be written as numbers. let v = 1 >>> accumulate (+) 0 which will sum the natural numbers. |
(Applicative m, Monad m, Monoid b) => Monoid (VarT m a b) Source | Streams can be monoids let v = var (const "Hello ") `mappend` var (const "World!") |
Creating value streams
You can create a pure value stream by lifting a function (a -> b)
with var
:
addsOne :: Monad m => VarT m Int Int addsOne = var (+1)
You can create a monadic value stream by lifting a monadic computation
(a -> m b)
using varM
:
getsFile :: VarT IO FilePath String getsFile = varM readFile
You can create either with the raw constructor. You can also create your own combinators using the raw constructor, as it allows you full control over how value streams are stepped and sampled:
delay :: Monad m => b -> VarT m a b -> VarT m a b delay b v = VarT $ a -> return (b, go a v) where go a v' = VarT $ a' -> do (b', v'') <- runVarT v' a return (b', go a' v'')
done :: (Applicative m, Monad m) => b -> VarT m a b Source
Lift a constant value into a stream.
var :: Applicative m => (a -> b) -> VarT m a b Source
Lift a pure computation into a stream.
Create a stream from a state transformer.
Composing value streams
You can compose value streams together using Arrow's >>>
and <<<
or the
synonyms ~>
and <~
. The "right plug" (>>>
and ~>
) takes the output
from a value stream on the left and "plugs" it into the input of the value
stream on the right.
The "left plug" does the same thing in the opposite direction. This allows
you to write value streams that read naturally.
Adjusting and accumulating
delay :: (Monad m, Applicative m) => b -> VarT m a b -> VarT m a b Source
Delays the given stream by one sample using the argument as the first sample. This enables the programmer to create streams that depend on themselves for values. For example:
let v = 1 + delay 0 v in testVar_ v
accumulate :: (Monad m, Applicative m) => (c -> b -> c) -> c -> VarT m b c Source
Accumulates input values using a folding function and yields that accumulated value each sample.
Sampling value streams (running and other entry points)
To sample a stream simply run it in the desired monad with
runVarT
. This will produce a sample value and a new stream.
do (sample, v') <- runVarT v inputValue
scanVar :: (Applicative m, Monad m) => VarT m a b -> [a] -> m ([b], VarT m a b) Source
Run the stream over the input values, gathering the output values in a list.
stepMany :: (Monad m, Functor m) => VarT m a b -> [a] -> a -> m (b, VarT m a b) Source
Iterate a stream over a list of input until all input is consumed, then iterate the stream using one single input. Returns the resulting output value and the new stream.
Tracing value streams in flight
vtrace :: (Applicative a, Show b) => VarT a b b Source
Trace the sample value of a stream and pass it along as output. This is very useful for debugging graphs of streams.
vstrace :: (Applicative a, Show b) => String -> VarT a b b Source
Trace the sample value of a stream with a prefix and pass the sample along as output. This is very useful for debugging graphs of streams.
vftrace :: Applicative a => (b -> String) -> VarT a b b Source
Trace the sample value after being run through a "show" function. This is very useful for debugging graphs of streams.