note 0.0.3 · OCaml Package

Signals.

A signal is a value that varies continuously over time. Consult the semantics.signalssemantics and notations

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of signals.

Signals

type 'a t = 'a signal

The type for signals of type 'a.

type 'a set = ?step:Step.t -> 'a -> unit

The type for functions setting signal values of type 'a. See create.

val obs : 'a t -> 'a Logr.obs

obs s is an observation for s.

val log : ?now:bool -> 'a signal -> ('a -> unit) -> Logr.t

log ?now s f is Logr.(create ~now (const f $ obs s)).

val create : ?eq:('a -> 'a -> bool) -> 'a -> 'a signal * 'a set

create v is a primitive signal set to the value v and a set function. The function set is such that:

set v sets the signal's value to v at the time it is called.
set ~step v sets the signal value to v at the time it is called and schedules an update at time step.

Warning. set must not be used in the definition of signals or events.

val eq : 'a signal -> 'a -> 'a -> bool

eq s is s's equality function.

val with_eq : ('a -> 'a -> bool) -> 'a signal -> 'a signal

with_eq eq s is s with equality function eq.

val value : 'a signal -> 'a

value s is the current value of s, [s]_t

val rough_value : 'a signal -> 'a

rough_value s is the current value of s, but in contrast to value it might not be exactly [s]_t.

val const : ?eq:('a -> 'a -> bool) -> 'a -> 'a signal

const v is always v, [const v]_t = v.

val hold : ?eq:('a -> 'a -> bool) -> 'a -> 'a event -> 'a signal

hold i e has the value of e's last occurrence or the value of i provides the signal value at creation time if there's no event at that time.

[hold i e]_t = i if [e]_≤t = None
[hold i e]_t = v if [e]_≤t = Some v

val bind : 'a signal -> ('a -> 'b signal) -> 'b signal

bind s f is the signal that results from applying f to s, [bind s f]_t = [f[s]_t]_t.

val join : 'a signal signal -> 'a signal

join ss is bind ss (fun s -> s).

val swap : 'a signal -> 'a signal event -> 'a signal

swap s se is join (hold ~eq:( == ) s se) that is the values of s followed by values of the last signal that occurred on se.

val changes : 'a signal -> 'a event

changes s occurs with the value of s whenever it changes.

[changes s]_t = Some v if [s]_t = v and [s]_t-dt = v' and eq v v' = false.
[changes s]_t = None otherwise.

Warning. By definition no event occurs if s changes at creation time (0 - dt is undefined).

val map : ?eq:('b -> 'b -> bool) -> ('a -> 'b) -> 'a signal -> 'b signal

map f s is s transformed by f, [map f s]_t = f [s]_t.

val app : ?eq:('b -> 'b -> bool) -> ('a -> 'b) signal -> 'a signal -> 'b signal

app sf s holds the value of sf applied to the value of s, [app sf s]_t = [sf]_t [s]_t.

val sample : 'b signal -> on:'a event -> ('b -> 'a -> 'c) -> 'c event

sample s ~on f samples s at e's occurrences.

[sample s ~on f]_t = Some (f sv ev) if [on]_t = Some ev and [s]_t = sv.
[sample s ~on f]_t = None otherwise.

val sample_filter : 
  'b signal ->
  on:'a event ->
  ('b -> 'a -> 'c option) ->
  'c event

sample_filter s on f is E.Option.on_some (sample s ~on f).

val snapshot : 'b signal -> on:'a event -> 'b event

snapshot ~on s is sample (fun v _ -> v) ~on s.

TODO. Candidate for deletion.

val accum : ?eq:('a -> 'a -> bool) -> 'a -> ('a -> 'a) event -> 'a signal

accum i e is hold i (E.accum i e).

val until : ?limit:bool -> ?init:'b -> next:'a event -> 'b signal -> 'b signal

until ~limit ~init ~next s is s until next occurs, after which the value s had just before (limit is false, default) or whenever next occurs (limit is true) is kept forever.

[until ~limit ~init ~next s]_t = [s]_t if [next]_≤t = None
[until ~limit ~init ~next s]_t = init if [next]₀ = Some _
[until ~limit:false ~init ~next s]_t = [s]_{t'- dt} if [next]_t' = Some _ and [next]_<t' = None.
[until ~limit:true ~init ~next s]_t = [s]_t' if [next]_t' = Some _ and [next]_<t' = None.

init defaults to value s.

val follow : ?init:'a -> 'a signal -> on:bool signal -> 'a signal

follow ~init s ~on is s whenever on is true and the last value of s when on was true if on is false. If on is false at creation time init is used (defaults to S.value s).

[follow ~init s ~on]₀ = [s]₀ if [on]₀ = true
[follow ~init s ~on]₀ = [init]₀ if [on]₀ = false
[follow ~init s ~on]_t = [s]_t if [on]_t = true
[follow ~init s ~on]_t = [follow ~init s ~on]_t' if [on]_t = false where t' is the greatest t' < t with [on]_t' = true or 0 if there is no such time.

val defer : ?init:'a -> 'a signal -> 'a signal

defer s is s delayed by an infinitesimal amount of time. At creation time init is used (defaults to S.value s).

[defer s]_t = init for t = 0.
[defer s]_t = [s]_t-dt otherwise.

val delay : 'a -> 'a signal Lazy.t -> 'a signal

delay i (lazy s) is the value s had an infinitesimal amount of time before:

[delay i (lazy s)]_t = i for t = 0.
[delay i (lazy s)]_t = [s']_t-dt otherwise.

val fix : ?eq:('a -> 'a -> bool) -> 'a -> ('a signal -> 'a signal * 'b) -> 'b

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 :

[s]_t = i for t = 0.
[s]_t = [s']_t-dt otherwise.

Lifting

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 signal -> 'b signal

val l2 : 
  ?eq:('c -> 'c -> bool) ->
  ('a -> 'b -> 'c) ->
  'a signal ->
  'b signal ->
  'c signal

val l3 : 
  ?eq:('d -> 'd -> bool) ->
  ('a -> 'b -> 'c -> 'd) ->
  'a signal ->
  'b signal ->
  'c signal ->
  'd signal

Stdlib types support

module Bool : sig ... end

Boolean signals

module Option : sig ... end

Option signals

module Pair : sig ... end

Pair signals.

package note

Signals

Lifting

Stdlib types support