Difference between revisions of "Netwire"

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Netwire is a library for [[Functional Reactive Programming|functional reactive programming]], which uses the concept of [[Arrow|arrows]] for modelling an embedded domain-specific languageThis language lets you express reactive systems, which means systems that change over time.  It shares the basic concept with [[Yampa]] and its fork Animas, but it is itself not a fork and has many additional features.
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Netwire is a [[Functional Reactive Programming|functional reactive programming]] library that provides both an applicative and an arrow interfaceIt allows you to express time-varying values with a rich event system.
 
 
* [http://hackage.haskell.org/package/netwire Download netwire]
 
 
 
This wiki page corresponds to Netwire version 3 and is currently a work in progress.
 
  
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* [http://hackage.haskell.org/package/netwire Project page]
 +
* [http://hub.darcs.net/ertes/netwire Source repository]
  
 
== Features ==
 
== Features ==
Line 10: Line 8:
 
Here is a list of some of the features of Netwire:
 
Here is a list of some of the features of Netwire:
  
* arrow interface (or optionally an applicative interface),
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* applicative interface (or optionally an arrow interface),
* signal inhibition (ArrowZero / Alternative),
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* signal intervals,
* signal selection (ArrowPlus / Alternative),
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* dynamic switching,
* self-adjusting wires (ArrowChoice),
+
* rich set of predefined functionality,
* rich set of event wires,
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* signal analysis (average, interpolation, peak, etc.),
* signal analysis wires (average, peak, etc.),
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* effectful reactive systems.
* effectful wires.
 
 
 
 
 
== Basics ==
 
 
 
The Netwire library is based around a data type called <hask>Wire</hask>.  You need to import the <hask>Control.Wire</hask> module to work with wires:
 
 
 
<haskell>
 
import Control.Wire
 
 
 
data Wire e (>~) a b
 
</haskell>
 
 
 
For some arrows <hask>(>~)</hask> and all monoids <hask>e</hask> the type <hask>Wire e (>~)</hask> is an arrow.  Only certain arrows are allowed for <hask>(>~)</hask>, because <hask>Wire</hask> is actually a data family.  These arrows are called base arrows in Netwire.
 
 
 
<haskell>
 
comp :: Wire e (>~) a b
 
</haskell>
 
 
 
Values of type <hask>Wire e (>~) a b</hask> are time-varying functions, which resemble the following type:
 
 
 
<haskell>
 
a >~ Either e b
 
</haskell>
 
 
 
So it's a function that takes a value of type <hask>a</hask> and either produces a value of type <hask>b</hask> or produces no value, but instead ''inhibits'' with a value of type <hask>e</hask>.  The act of running a wire is called ''stepping'' and the process is called an ''instant''.  You can step a wire through one of the stepping functions, which we will cover later.  When you step a wire, it will return a new version of itself along with its result.  You are supposed to call the new version the next time you step.
 
 
 
=== The inhibition monoid ===
 
 
 
The <hask>e</hask> argument to <hask>Wire</hask> is called the inhibition monoid.  For simple applications you can just use <hask>()</hask> here, but you may want to actually assign exception values to inhibition.  We will cover that later.  For now just use <hask>()</hask>.
 
 
 
=== Base arrows ===
 
 
 
The <hask>(>~)</hask> argument to <hask>Wire</hask> is called the base arrow.  In most cases you will use a <hask>Kleisli</hask> arrow here, and this is currently the only type of arrow supported, though more will be added in the future.  For simple applications you can just use the <hask>IO</hask> monad, and it is useful to define a type alias for your custom wire type:
 
 
 
<haskell>
 
type MyWire = Wire () (Kleisli IO)
 
</haskell>
 
 
 
 
 
== Running wires ==
 
 
 
For running a wire you can use the stepping functions available in the <hask>Control.Wire.Session</hask> module.  There is no need to import that module.  It is automatically imported with <hask>Control.Wire</hask>. For Kleisli-based wires you will want to use the <hask>stepWireM</hask> function:
 
 
 
<haskell>
 
stepWireM ::
 
    Monad m
 
    => Wire e (Kleisli m) a b
 
    -> a
 
    -> m (Either e b, Wire e (Kleisli m) a b)
 
</haskell>
 
 
 
In our case we have <hask>m = IO</hask>, so our type signature is simply:
 
  
<haskell>
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== Scope ==
stepWireM :: MyWire a b -> a -> IO (Either () b, MyWire a b)
 
</haskell>
 
  
This function takes a wire and an input value.  It passes the input value to the wire and returns its result value of type <hask>Either () b</hask>.  Along with the result it also returns a new wireNormally you would call <hask>stepWireM</hask> in a loop, which performs instant after instant.  This is the basic structure:
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Netwire's FRP framework is intended to be used for continuous applications.  It replaces the traditional big main loop with its global state and event callbacks/branching by a completely declarative modelThe following types of applications can benefit from using Netwire:
  
<haskell>
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* artificial intelligence and bots,
system :: MyWire Int String
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* canvas-based graphics and animations,
system = {- ... -}
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* continuous signal synthesis (audio waves, etc.),
 +
* games and game servers,
 +
* scene-based user interfaces (like OpenGL and vty),
 +
* simulations.
  
main :: IO ()
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If you can sensibly break your application down into ''frames'', then Netwire is for you.  For other kinds of reactive applications like widget-based UIs you may want to look into [[reactive-banana]] instead.
main = loop system
 
    where
 
    loop :: MyWire Int String -> IO ()
 
    loop w' = do
 
        (mx, w) <- stepWireM w' 15
 
  
        {- ... do something with mx ... -}
 
  
        loop w  -- loop with the new wire.
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== Get started ==
</haskell>
 
  
Note:  Even though the FRP idea suggests it, there is no reason to run wires continuously or even regularly.  You can totally have an instant depending on user input, a GUI event or network traffic, so instants can be minutes apart.
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The documentation is contained within the package itself, but you can also read it online:
  
=== Testing wires ===
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* [http://hub.darcs.net/ertes/netwire/browse/README.md Tutorial]
 +
* [http://hackage.haskell.org/package/netwire Project page with API docs]
  
There is a convenient function for testing wires, which does all the plumbing for you.  It's called <hask>testWireM</hask>:
 
  
<haskell>
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=== Other reading ===
testWireM ::
 
    (Show e, MonadIO m)
 
    => Int
 
    -> m a
 
    -> Wire e (Kleisli m) a String
 
    -> m ()
 
</haskell>
 
  
For wires returning a string, you can easily test them using this function.  The first argument is a FPS/accuracy tradeoff. If it's 100, it will only print the output of every 100th instant. The second argument is an input generator action.  At each instant, this action is run and its result is passed as input to the wire.  The wire's output is then printed.  <hask>testWireM</hask> prints the output continuously on a single line:
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* [http://todayincode.tumblr.com/post/96914679355/almost-a-netwire-5-tutorial Almost a Netwire 5 Tutorial]
  
<haskell>
 
main :: IO ()
 
main = testWireM 1000 (return 15) system
 
</haskell>
 
  
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=== Examples ===
  
== Predefined wires ==
+
* [https://github.com/ScrambledEggsOnToast/tetris-hs tetris-hs]
  
There are numerous predefined wires, which you can compose using the arrow interface.  We will practice that with three very simple predefined wires (the type signatures are simplified for the sake of learning):
 
  
<haskell>
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== Model and correctness ==
constant  :: b -> Wire e (>~) a b
 
identity  :: Wire e (>~) b b
 
countFrom :: Enum b => b -> Wire e (>~) a b
 
</haskell>
 
  
The ''constant'' function takes an output value and produces a wire which produces that value constantly.  So the wire <hask>constant 15</hask> will output 15 constantly at every instant. In other words, <hask>stepWireM</hask> will return <hask>Right 15</hask> along with a new wire that outputs 15 again:
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Netwire's underlying abstraction is more powerful than the [http://conal.net/papers/icfp97/ original formulation of time-varying values].  It allows you to implement general component systems with local state.
  
<haskell>
+
Starting with Netwire 5 there are two module trees <hask>Control.Wire</hask> and <hask>FRP.Netwire</hask>.  The latter exports a subset of Netwire that closely follows the original model and provides a set of predefined FRP wires.
stepWireM (constant 15) inp
 
-> (Right 15, constant 15)
 
</haskell>
 
  
Note the fully polymorphic input type <hask>a</hask>.  This basically means that the wire disregards its input, so whatever <hask>inp</hask> is, it is ignored.
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Signal intervals are an extension of the original model and an integral part of Netwire:  A behavior is a ''partial'' function of time with the limitation that both the defined and undefined intervals must have a non-zero length.  This extension makes it much easier to express switching and multicasting systems.
  
The ''identity'' wire is slightly more interesting.  It has input and output of type <hask>b</hask>.  What it does is:  It simply outputs its input value at every instant:
+
== History ==
  
<haskell>
+
This project started in 2011 as a replacement for Yampa to provide both a nicer interface and better integration into existing frameworks.  Its original purpose was to power game servers and intelligent network bots.  That's the origin of the name ''Netwire''.
stepWireM identity inp
 
-> (Right inp, identity)
 
</haskell>
 
  
Both identity and constant wires are examples of ''stateless'' wires.  They don't change over timeYou can see this in the stepping examples above.  They always return themselves for the next instant.
+
However, before its first release ''signal intervals'' were added (originally under the term ''signal inhibition'')Netwire became a completely new abstraction, so it lost its connection to Yampa.
  
 
[[Category:FRP]]
 
[[Category:FRP]]

Latest revision as of 21:39, 2 October 2014

Netwire is a functional reactive programming library that provides both an applicative and an arrow interface. It allows you to express time-varying values with a rich event system.

Features

Here is a list of some of the features of Netwire:

  • applicative interface (or optionally an arrow interface),
  • signal intervals,
  • dynamic switching,
  • rich set of predefined functionality,
  • signal analysis (average, interpolation, peak, etc.),
  • effectful reactive systems.

Scope

Netwire's FRP framework is intended to be used for continuous applications. It replaces the traditional big main loop with its global state and event callbacks/branching by a completely declarative model. The following types of applications can benefit from using Netwire:

  • artificial intelligence and bots,
  • canvas-based graphics and animations,
  • continuous signal synthesis (audio waves, etc.),
  • games and game servers,
  • scene-based user interfaces (like OpenGL and vty),
  • simulations.

If you can sensibly break your application down into frames, then Netwire is for you. For other kinds of reactive applications like widget-based UIs you may want to look into reactive-banana instead.


Get started

The documentation is contained within the package itself, but you can also read it online:


Other reading


Examples


Model and correctness

Netwire's underlying abstraction is more powerful than the original formulation of time-varying values. It allows you to implement general component systems with local state.

Starting with Netwire 5 there are two module trees Control.Wire and FRP.Netwire. The latter exports a subset of Netwire that closely follows the original model and provides a set of predefined FRP wires.

Signal intervals are an extension of the original model and an integral part of Netwire: A behavior is a partial function of time with the limitation that both the defined and undefined intervals must have a non-zero length. This extension makes it much easier to express switching and multicasting systems.

History

This project started in 2011 as a replacement for Yampa to provide both a nicer interface and better integration into existing frameworks. Its original purpose was to power game servers and intelligent network bots. That's the origin of the name Netwire.

However, before its first release signal intervals were added (originally under the term signal inhibition). Netwire became a completely new abstraction, so it lost its connection to Yampa.