Signals are the key concept of Functional Reactive Programming. They describe behavior over
time. This module provides general support for signals. Individual kinds of signals are provided
by the submodules FRP.Grapefruit.Signal.Disrete, FRP.Grapefruit.Signal.Segmented and
A signal type has kind * -> * -> *. Its first parameter denotes the time interval in which the
signal is alive. This is called the era of the signal. An era is left-closed (contains a
starting time) but right-open or right-unbounded (does not contain an ending time).
The era type parameter is not intended to be instantiated with concrete types. Instead, it is
used to force equality of eras or independence of eras at compile time. Its use is very similar
to that of the first type parameter of ST and the first parameter of STRef.
|The class of all signal types.
This function generates a signal whose behavior switches between that of different other
signals over time.
Since the result type SignalFun era shape is isomorphic to an n-ary function type, we
can see switch as a function which takes a first argument, called the function signal,
and n further arguments, called the argument signals, and yields a signal, called the
The result signal is composed of different sections. There is one section for each segment
of the function signal. Such a section is formed as follows: For each argument signal, the
part which corresponds to the time intervall of the functions signal’s segment is cut
out of the argument signal. The value of the function signal is applied to the resulting n
signal parts. The result of this application is the desired section of the result signal.
The signal functions which are applied to the parts of the argument signals use an
universally quantified era parameter. This ensures that the results of these functions do
not depend on signals from the outside but only on the parts of the argument signals. This
is important since operations on signals require that their argument and result signals are
of the same era. The usage of universial quantification in the type of switch
corresponds to the usage of rank 2 polymorphism in the type of runST.
|data SignalFun era shape where||Source|
A signal function is a function which maps a certain number of signals to one signal whereby
all argument signals and the result signal have the same era.
The era parameter of SignalFun denotes the era of all argument signals and the result
signal. The shape parameter is a phantom parameter which specifies the number of argument
signals as well as the types of the argument signals and the result signal without their era
parameters. It has the following form:
signal_1 `Of` val_1 :-> ... :-> signal_n `Of` val_n :-> signal' `Of` val'
The data constructors OSF and SSF construct signal functions of zero and non-zero arity,
respectively. (The O stands for “zero” and the S stands for
“successor”.) A signal function is typically formed by an expression like
SSF $ \signal_1 ->
SSF $ \signal_n ->
OSF $ signal'
where signal' is an expression that might use signal_1 to signal_n. Signal
functions are usually applied like this:
unOSF $ signalFun `sfApp` signal_1 `sfApp` ... `sfApp` signal_n
|Converts a nullary signal function into its corresponding signal.
|Converts a signal function of non-zero arity into a true function.
Applies a signal function to a signal.
sfApp is equivalent to unSSF.
|data argShape :-> resultShape ||Source|
|The :-> operator is used to form signal function shapes for SignalFun. The shape
argShape :-> resultShape stands for functions which map signals of shape argShape
to signal functions of shape resultShape.
Of is used to form signal shapes. Signal shapes are used as phantom types and denote a
signal type except its era parameter.
A signal shape signal `Of` val stands for a signal of type signal era
val where the era parameter is provided by an external source. Signal shapes are used as
signal function shapes of nullary functions and as argument shapes for :->. In this case,
the era parameter is the era parameter of SignalFun. Signal shapes are also used in
records as defined by the module FRP.Grapefruit.Record of package grapefruit-records.
|The class of all signals which can be seen as discrete sequences of values. Such signals can
be used to sample signals of class Samplee.
|The class of all signals which assign a value to each time of their era. Such signals can be
sampled by signals of class Sampler.
|(<#>) :: (Sampler sampler, Samplee samplee) => sampler era (val -> val') -> samplee era val -> sampler era val'||Source|
Sampling of signals.
A signal sampler <#> samplee has a value at each time where sampler has a
value. The value of sampler <#> samplee is formed by applying the value of
sampler to the value, samplee has at this time.
This function has similarities with <*>.
|(#>) :: (Sampler sampler, Samplee samplee) => sampler era dummy -> samplee era val -> sampler era val||Source|
Sampling of signals where the values of the sampler are ignored.
The following equation holds:
sampler #> samplee = id <$ sampler <#> samplee
This function has similarities with *>.
|(<#) :: (Sampler sampler, Samplee samplee) => sampler era val -> samplee era dummy -> sampler era val||Source|
Sampling of signals where the values of the samplee are ignored.
The following equation holds:
sampler <# samplee = const <$> sampler <#> samplee
This function has similarities with <*.
|newtype Consumer signal val ||Source|
|A consumer says what to do with a given signal.
|Consumer (forall era. Circuit era (signal era val) ())||A consumer, represented by a circuit that consumes a signal.
|Yields a circuit which consumes a signal.
|newtype Producer signal val ||Source|
|A producer says how to produce a certain signal.
|Producer (forall era. Circuit era () (signal era val))||A producer, represented by a circuit that produces a signal.
|Yields a circuit which produces a signal.
|Produced by Haddock version 2.4.2|