Module Fut

Future values.

A future 'a Fut.t is an undetermined value of type 'a that becomes determined at an arbitrary point in the future. The future acts as a placeholder for the value while it is undetermined.

Brr uses future values ('a, 'b) result Fut.t to type the resolution and rejection case of JavaScript promises. Since most rejection cases given by browser APIs are simply Jv.Error.t values, the dedicated Fut.or_error type alias can be used for that.

Fut.t values are indirectly implemented as Promise objects that never reject. You can't substitute them directly for JavaScript promises and vice-versa, use of_promise and to_promise to convert between them.


type 'a t

The type for futures with value of type 'a.

val create : unit -> 'a t * ('a -> unit)

create () is (f, set with f the future value and set the function to set it. The latter can be called only once, a Jv.Error is thrown otherwise.

val await : 'a t -> ('a -> unit) -> unit

await f k waits for f to determine v and continues with k v. If the future never determines k is not invoked. k must not raise.

val return : 'a -> 'a t

return v is a future that determines v.

val map : ('a -> 'b) -> 'a t -> 'b t

map fn f is return (fn v) with v the value determined by f.

val bind : 'a t -> ('a -> 'b t) -> 'b t

bind f fn is the future fn v with v the value determined by f.

val pair : 'a t -> 'b t -> ('a * 'b) t

pair f0 f1 is the future that determines with the value of f0 and f1.

val of_list : 'a t list -> 'a list t

of_list fs determines with the values of all future fs in the same order.

val tick : ms:int -> unit t

tick ~ms determines () ms milliseconds after creation using setTimeout.

Future results

type nonrec ('a, 'b) result = ('a, 'b) Stdlib.result t

The type for future values that may error.

type 'a or_error = ('a, Jv.Error.t) result

The type for future values that error with a JavaScript error.

val ok : 'a -> ('a, 'b) result

ok v is return (Ok v).

val error : 'b -> ('a, 'b) result

error e is return (Error e).

Converting with JavaScript promises

val of_promise : ok:(Jv.t -> 'a) -> Jv.Promise.t -> 'a or_error

of_promise ~ok p is of_promise' ~ok ~error:Jv.to_error. p.

val to_promise : ok:('a -> Jv.t) -> 'a or_error -> Jv.Promise.t

to_promise p is to_promise' ~ok ~error:Jv.of_error p.

val of_promise' : ok:(Jv.t -> 'a) -> error:(Jv.t -> 'b) -> Jv.Promise.t -> ('a, 'b) result

of_promise ~ok ~error p is a future for the promise p. The future determines with Ok (ok v) if p resolves with v and with Error (error e) if p rejects with e.

val to_promise' : ok:('a -> Jv.t) -> error:('b -> Jv.t) -> ('a, 'b) result -> Jv.Promise.t

to_promise f is a JavaScript promise for the future f that resolves the promise with ok v if the future determines with Ok v and rejects with e if the future determines with Error e.

Future syntaxes

module Syntax : sig ... end

Future syntax.

module Result_syntax : sig ... end

Future result syntax.