Module Async_or_error

module Async_or_error: sig .. end
This module is the deferred analog of Core.Or_error. It is exposed in 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 one 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.

type 'a t = 'a Core.Std.Or_error.t Deferred.t 
include Monad.S
return x = Deferred.return (Ok x) *
val fail : Core.Std.Error.t -> 'a 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 -> 'a t
val of_exn_result : ('a, exn) Core.Std.Result.t Deferred.t -> 'a t
val error : string -> 'a -> ('a -> Core.Std.Sexp.t) -> 'b t
val error_string : string -> 'a t
val unimplemented : string -> 'a t
val combine_errors : 'a t list -> 'a list t
val combine_errors_unit : unit t list -> unit t
val ok_unit : unit t
ok_unit = return ()
val try_with : ?extract_exn:bool ->
?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).

val try_with_join : ?extract_exn:bool ->
?name:string -> (unit -> 'a t) -> 'a t
module List: Deferred_intf.Monad_sequence 
  with type 'a monad := 'a t 
    with type 'a t := 'a list