Module React.S

module S: sig .. end
Signal combinators.

Consult their semantics.

Primitive and basics

type 'a t = 'a React.signal 
The type for signals of type 'a.
val const : 'a -> 'a React.signal
const v is always v, [const v]t = v.
val create : ?eq:('a -> 'a -> bool) ->
'a -> 'a React.signal * (?step:React.step -> 'a -> unit)
create i is a primitive signal s set to i and a set function. The function set is such that: Warning. set must not be executed inside an update step.
val value : 'a React.signal -> 'a
value s is s's current value.

Warning. If executed in an update step may return a non up-to-date value or raise Failure if the signal is not yet initialized.

val retain : 'a React.signal -> (unit -> unit) -> [ `R of unit -> unit ]
retain s c keeps a reference to the closure c in s and returns the previously retained value. c will never be invoked.

Raises. Invalid_argument on constant signals.

val stop : ?strong:bool -> 'a React.signal -> unit
stop s, stops updating s. It conceptually becomes React.S.const with the signal's last value and cannot be restarted. Allows to disable effectful signals.

The strong argument should only be used on platforms where weak arrays have a strong semantics (i.e. JavaScript). See details.

Note. If executed in an update step the signal may still update in the step.

val equal : ?eq:('a -> 'a -> bool) -> 'a React.signal -> 'a React.signal -> bool
equal s s' is true iff s and s' are equal. If both signals are React.S.constant eq is used between their value (defauts to structural equality). If both signals are not React.S.constant, physical equality is used.
val trace : ?iff:bool t -> ('a -> unit) -> 'a React.signal -> 'a React.signal
trace iff tr s is s except tr is invoked with s's current value and on s changes when iff is true (defaults to S.const true). For all t where [s]t = v and (t = 0 or ([s]t-dt= v' and eq v v' = false)) and [iff]t = true, tr is invoked with v.

From events

val hold : ?eq:('a -> 'a -> bool) -> 'a -> 'a React.event -> 'a React.signal
hold i e has the value of e's last occurrence or i if there wasn't any.

Transforming and filtering

val app : ?eq:('b -> 'b -> bool) ->
('a -> 'b) React.signal -> 'a React.signal -> 'b React.signal
app sf s holds the value of sf applied to the value of s, [app sf s]t = [sf]t [s]t.
val map : ?eq:('b -> 'b -> bool) -> ('a -> 'b) -> 'a React.signal -> 'b React.signal
map f s is s transformed by f, [map f s]t = f [s]t.
val filter : ?eq:('a -> 'a -> bool) ->
('a -> bool) -> 'a -> 'a React.signal -> 'a React.signal
filter f i s is s's values that satisfy p. If a value does not satisfy p it holds the last value that was satisfied or i if there is none.
val fmap : ?eq:('b -> 'b -> bool) ->
('a -> 'b option) -> 'b -> 'a React.signal -> 'b React.signal
fmap fm i s is s filtered and mapped by fm.
val diff : ('a -> 'a -> 'b) -> 'a React.signal -> 'b React.event
diff f s is an event with occurrences whenever s changes from v' to v and eq v v' is false (eq is the signal's equality function). The value of the occurrence is f v v'.
val changes : 'a React.signal -> 'a React.event
changes s is diff (fun v _ -> v) s.
val sample : ('b -> 'a -> 'c) -> 'b React.event -> 'a React.signal -> 'c React.event
sample f e s samples s at e's occurrences.
val on : ?eq:('a -> 'a -> bool) ->
bool React.signal -> 'a -> 'a React.signal -> 'a React.signal
on c i s is the signal s whenever c is true. When c is false it holds the last value s had when c was the last time true or i if it never was.
val when_ : ?eq:('a -> 'a -> bool) ->
bool React.signal -> 'a -> 'a React.signal -> 'a React.signal
Deprecated.Use React.S.on.
val dismiss : ?eq:('a -> 'a -> bool) ->
'b React.event -> 'a -> 'a React.signal -> 'a React.signal
dismiss c i s is the signal s except changes when c occurs are ignored. If c occurs initially i is used.


val accum : ?eq:('a -> 'a -> bool) -> ('a -> 'a) React.event -> 'a -> 'a React.signal
accum e i is S.hold i (React.E.accum e i).
val fold : ?eq:('a -> 'a -> bool) ->
('a -> 'b -> 'a) -> 'a -> 'b React.event -> 'a React.signal
fold f i e is S.hold i (React.E.fold f i e).


val merge : ?eq:('a -> 'a -> bool) ->
('a -> 'b -> 'a) -> 'a -> 'b React.signal list -> 'a React.signal
merge f a sl merges the value of every signal in sl using f and the accumulator a.

[merge f a sl]t = List.fold_left f a ( []t sl).

val switch : ?eq:('a -> 'a -> bool) -> 'a React.signal React.signal -> 'a React.signal
switch ss is the inner signal of ss.
val bind : ?eq:('b -> 'b -> bool) ->
'a React.signal -> ('a -> 'b React.signal) -> 'b React.signal
bind s sf is switch (map ~eq:( == ) sf s).
val fix : ?eq:('a -> 'a -> bool) ->
'a -> ('a React.signal -> 'a React.signal * 'b) -> 'b
fix i sf allow to refer to the value a signal had an infinitesimal amount of time before.

In fix sf, sf is called with a signal s that represents the signal returned by sf delayed by an infinitesimal amount time. If s', r = sf s then r is returned by fix and s is such that :

eq is the equality used by s.

Raises. Invalid_argument if s' is directly a delayed signal (i.e. a signal given to a fixing function).

Note. Regarding values depending on the result r of s', r = sf s the following two cases need to be distinguished :


Lifting combinators. For a given n the semantics is :

[ln f a1 ... an]t = f [a1]t ... [an]t

val l1 : ?eq:('b -> 'b -> bool) -> ('a -> 'b) -> 'a React.signal -> 'b React.signal
val l2 : ?eq:('c -> 'c -> bool) ->
('a -> 'b -> 'c) -> 'a React.signal -> 'b React.signal -> 'c React.signal
val l3 : ?eq:('d -> 'd -> bool) ->
('a -> 'b -> 'c -> 'd) ->
'a React.signal -> 'b React.signal -> 'c React.signal -> 'd React.signal
val l4 : ?eq:('e -> 'e -> bool) ->
('a -> 'b -> 'c -> 'd -> 'e) ->
'a React.signal ->
'b React.signal -> 'c React.signal -> 'd React.signal -> 'e React.signal
val l5 : ?eq:('f -> 'f -> bool) ->
('a -> 'b -> 'c -> 'd -> 'e -> 'f) ->
'a React.signal ->
'b React.signal ->
'c React.signal -> 'd React.signal -> 'e React.signal -> 'f React.signal
val l6 : ?eq:('g -> 'g -> bool) ->
('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g) ->
'a React.signal ->
'b React.signal ->
'c React.signal ->
'd React.signal -> 'e React.signal -> 'f React.signal -> 'g React.signal

The following modules lift some of Pervasives functions and operators.
module Bool: sig .. end
module Int: sig .. end
module Float: sig .. end
module Pair: sig .. end
module Option: sig .. end
module Compare: sig .. end

Combinator specialization

Given an equality function equal and a type t, the functor React.S.Make automatically applies the eq parameter of the combinators. The outcome is combinators whose results are signals with values in t.

Basic types are already specialized in the module React.S.Special, open this module to use them.

module type EqType = sig .. end
Input signature of React.S.Make
module type S = sig .. end
Output signature of React.S.Make
module Make: 
functor (Eq : EqType) -> S with type 'a v = 'a Eq.t
Functor specializing the combinators for the given signal value type
module Special: sig .. end
Specialization for booleans, integers and floats.