Control.Tweak.Var

Var is the reference type used for incremental computing. It has a cached value and a list of dependent children to update when it changes.

The update propogation happens automatically when using either modifyVar or writeVar. Same with the STM variants.

Additionally updates can be triggered manually with update

Var is low level and is used by Tweakable and to create incremental expressions.

Reference for Incremental Computing

data Var a

This a reference for incremental computation. Not only does it include a value, But is also has a list of actions to execute when it is updated.

Constructors

Var

Fields

_output :: TVar a

The cached value of the the Var

_children :: TVar Children

A collection of actions to execute when the value of the Var is updated

_identifier :: Unique

This is so to references to the same Var are not added to _children collection

Instances

Comply Maker Var

Funktor Maker Var

Eq (Var a)

Just checks pointer equality not value equality

Ord (Var a)

Cacheable (Var a)

Existential Var Wrapper

data AnyVar

Constructors

forall a . AnyVar (Var a)

Instances

Eq AnyVar

Ord AnyVar

Cacheable AnyVar

Helpers

type Update = STM ()

The type of update actions

type Children = Map AnyVar Update

The container for a Vars dependent Vars.

class Cacheable a where

Methods

children :: Lens' a (TVar Children)

Instances

Cacheable AnyVar

Cacheable (Var a)

Cacheable (Tweakable a)

Lenses

output :: Lens (Var a) (Var b) (TVar a) (TVar b)

a Lens for the cached ref

identifier :: Lens (Var a) (Var a) Unique Unique

a Lens for the unique identifier associated with this Var

Dependency Manipulation

update :: Cacheable a => a -> STM ()

Recursively call update on the children of a Var like thing

addChild

Arguments

:: Cacheable a

=> a

The input that contains the reference to add children to

-> AnyVar

The child Var existentially wrapped up. The important info here is the unique Var id.

-> Update

The update action to call when the input is updated.

-> IO ()

Add a dependent child to the Vars children, or any type that has Var like Children See addChildSTM for the STM version

addChildSTM

Arguments

:: Cacheable a

=> a

The input that contains the reference to add children to

-> AnyVar

The child Var existentially wrapped up. The important info here is the unique Var id.

-> Update

The update action to call when the input is updated.

-> STM ()

Add a dependent child to the Vars children, or any type that has Var like Children See addChild for the IO version

Var IO CRU

newVar :: a -> IO (Var a)

Create a new Var. See newVarSTM for the STM version.

readVar :: Var a -> IO a

Read the cached value of a Var. See readVarSTM for an STM version

modifyVar :: Var a -> (a -> a) -> IO ()

Modify a Var and update the children. See modifyVarSTM for the STM version

writeVar :: Var a -> a -> IO ()

Write a new value into a Var and update all of the children. See writeVarSTM for the STM version

Var STM CRU

newVarSTM :: a -> STM (Var a)

Create a new Var. See newVar for the IO version.

readVarSTM :: Var a -> STM a

Read the cached value of a Var. See readVar for an IO version

modifyVarSTM :: Var a -> (a -> a) -> STM ()

Modify a Var and update the children. See modifyVar for the IO version

writeVarSTM :: Var a -> a -> STM ()

Write a new value into a Var and update all of the children. See writeVar for the IO version