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
- data VarT m a b = VarT {}
- 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 => VarT m b c -> VarT m a b -> VarT m a c
- (~>) :: Monad m => VarT m a b -> VarT m b c -> VarT m a c
- delay :: Monad m => b -> VarT m a b -> VarT m a b
- accumulate :: Monad m => (c -> b -> c) -> c -> VarT m b c
- evalVar :: Functor m => VarT m a b -> a -> m b
- execVar :: Functor m => VarT m a b -> a -> m (VarT m a b)
- loopVar :: Monad m => a -> VarT m a a -> m a
- loopVar_ :: (Functor m, Monad m) => VarT m () a -> m ()
- whileVar :: Monad m => (a -> Bool) -> a -> VarT m a a -> m a
- whileVar_ :: Monad m => (a -> Bool) -> VarT m () a -> m a
- scanVar :: (Applicative m, Monad m) => VarT m a b -> [a] -> m [b]
- stepMany :: (Monad m, Functor m, Monoid a) => [a] -> VarT m a b -> m (b, VarT m a b)
- testVar :: (Read a, Show b) => VarT IO a b -> IO ()
- testVar_ :: Show b => VarT IO () b -> IO ()
- testWhile_ :: Show a => (a -> Bool) -> VarT IO () a -> IO ()
- 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.
(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'')
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 ~>
and <~
. The "right plug"
(~>
) 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.
(<~) :: Monad m => VarT m b c -> VarT m a b -> VarT m a c infixl 1 Source
Same as ~>
with flipped parameters.
Adjusting and accumulating
delay :: Monad 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 => (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)
The easiest way to sample a stream is to run it in the desired monad with
runVarT
. This will produce a sample value and a new stream.
do (sample, v') <- runVarT v inputValue
Much like Control.Monad.State there are other entry points for running
value streams like evalVar
, execVar
. There are also extra control
structures such as loopVar
and whileVar
.
evalVar :: Functor m => VarT m a b -> a -> m b Source
Iterate a stream once and return the sample value.
execVar :: Functor m => VarT m a b -> a -> m (VarT m a b) Source
Iterate a stream once and return the next stream.
loopVar :: Monad m => a -> VarT m a a -> m a Source
Loop over a stream that produces its own next input value.
loopVar_ :: (Functor m, Monad m) => VarT m () a -> m () Source
Loop over a stream that takes no input value.
:: Monad m | |
=> (a -> Bool) | The predicate to evaluate samples. |
-> a | The initial input/sample value. |
-> VarT m a a | The stream to iterate |
-> m a | The last sample |
Iterate a stream that produces its own next input value until the given predicate fails.
whileVar_ :: Monad m => (a -> Bool) -> VarT m () a -> m a Source
Iterate a stream that requires no input until the given predicate fails.
scanVar :: (Applicative m, Monad m) => VarT m a b -> [a] -> m [b] Source
Run the stream over the input values, gathering the output values in a list.
stepMany :: (Monad m, Functor m, Monoid a) => [a] -> VarT m a b -> m (b, VarT m a b) Source
Iterate a stream using a list of input until all input is consumed and output the result.
Testing value streams
testVar_ :: Show b => VarT IO () b -> IO () Source
A utility function for testing streams that don't require input. Use
this in GHCI to step through your streams using the return
key.
testWhile_ :: Show a => (a -> Bool) -> VarT IO () a -> IO () Source
A utility function for testing streams that don't require input. Runs a stream printing each sample until the given predicate fails.
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.