async_kernel v0.15.0 · OCaml Package

The deferred analog of Core.Or_error. It is exposed in std.ml as Deferred.Or_error.

The mental model for a function returning an 'a Deferred.Or_error.t is that the function never raises. All error cases are caught and expressed as an Error _ result. This module preserves that property.

Unfortunately, there is no way to enforce this property using the type system, so it is more like a convention, or idiom. A function whose type ends with ... -> 'a Deferred.Or_error.t and still raises should be considered broken, and be fixed. With that property in mind, Deferred.Or_error.List.iter, for example, does not wrap the execution of the given iter function f inside a monitor. If one of these application raises, the whole function Deferred.Or_error.List.iter will raise as a way to try to alert the developer that the function is broken and needs attention and fixing, rather than silently catching the error and converting it to Or_error.Error.

This behavior is consistent with Core.Or_error's treatment of user-supplied functions.

If you have to deal with a function that does not respect this idiom, you can use Deferred.Or_error.try_with_join to wrap its execution and enforce this property.

module Deferred : sig ... end

type 'a t = 'a Core.Or_error.t Deferred.t

The applicative operations match the behavior of the applicative operations in Or_error. This means that all and all_unit are equivalent to combine_errors and combine_errors_unit respectively.

include Core.Applicative.S with type 'a t := 'a t

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

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

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

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

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

val map2 : 'a t -> 'b t -> f:('a -> 'b -> 'c) -> 'c t

val map3 : 'a t -> 'b t -> 'c t -> f:('a -> 'b -> 'c -> 'd) -> 'd t

module Applicative_infix : sig ... end

return x = Deferred.return (Ok x) *

include Core.Monad.S with type 'a t := 'a t

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

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

module Monad_infix : sig ... end

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

val return : 'a -> 'a t

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

val join : 'a t t -> 'a t

val ignore_m : 'a t -> unit t

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

val all_unit : unit t list -> unit t

module Let_syntax : sig ... end

val fail : Core.Error.t -> _ t

fail error = Deferred.return (Error error) *

val ok_exn : 'a t -> 'a Deferred.t

These functions are direct analogs of the corresponding Core.Or_error functions.

val of_exn : exn -> _ t

val of_exn_result : ('a, exn) Core.Result.t Deferred.t -> 'a t

val error : string -> 'a -> ('a -> Core.Sexp.t) -> _ t

val error_s : Core.Sexp.t -> _ t

val error_string : string -> _ t

val errorf : ('a, unit, string, _ t) Core.format4 -> 'a

val tag : 'a t -> tag:string -> 'a t

val tag_s : 'a t -> tag:Core.Sexp.t -> 'a t

val tag_s_lazy : 'a t -> tag:Core.Sexp.t Core.Lazy.t -> 'a t

val tag_arg : 'a t -> string -> 'b -> ('b -> Core.Sexp.t) -> 'a t

val unimplemented : string -> _ t

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

val combine_errors_unit : unit t list -> unit t

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

val find_map_ok : 'a list -> f:('a -> 'b t) -> 'b t

find_map_ok l ~f returns the first value in l for which f returns Ok, otherwise it returns the same error as combine_errors (Deferred.List.map l ~f).

val ok_unit : unit t

ok_unit = return ()

val try_with : 
  ?extract_exn:bool ->
  ?run:[ `Now | `Schedule ] ->
  ?rest:[ `Log | `Raise | `Call of exn -> unit ] ->
  ?here:Stdlib.Lexing.position ->
  ?name:string ->
  (unit -> 'a Deferred.t) ->
  'a t

try_with f catches exceptions thrown by f and returns them in the Result.t as an Error.t. try_with_join is like try_with, except that f can throw exceptions or return an Error directly, without ending up with a nested error; it is equivalent to try_with f >>| Result.join.

The option extract_exn is passed along to Monitor.try_with ?extract_exn and specifies whether or not the monitor exn wrapper should be skipped (extract_exn:true or kept (extract_exn:false).

The ~rest argument controls how exceptions are handled after the try_with deferred becomes determined. They may be logged, raised, or passed to a callback.

The ~run argument controls when f gets called. `Now calls f immediately; `Schedule schedules an asynchronous job to run f.

val try_with_join : 
  ?extract_exn:bool ->
  ?run:[ `Now | `Schedule ] ->
  ?rest:[ `Log | `Raise | `Call of exn -> unit ] ->
  ?here:Stdlib.Lexing.position ->
  ?name:string ->
  (unit -> 'a t) ->
  'a t

module List : 
  Monad_sequence.S with type 'a monad := 'a t with type 'a t := 'a list

All of the List functions that take a how argument treat it the following way:

val repeat_until_finished : 
  'state ->
  ('state -> [ `Repeat of 'state | `Finished of 'result ] t) ->
  'result t

repeat_until_finished initial_state f works just like Deferred.repeat_until_finished but with the Deferred.Or_error monad. If f returns an Or_error.Error the loop terminates and returns.

package async_kernel