Module Async_kernel__.Lazy_deferred
A delayed computation that can produce a deferred.
Nothing happens with a lazy deferred unless one force
s it. Forcing a lazy deferred starts the computation, which will eventually cause the deferred to become determined. As usual with laziness, multiply forcing a lazy deferred is no different than forcing it a single time.
Exceptions (both synchronous and asynchronous) raised by a delayed computation are returned by force
(wait
, peek
, etc.), or will be raised to the monitor in effect when force_exn
(wait_exn
, peek_exn
, etc.) was called.
The type is not exposed nor defined as 'a Deferred.t Lazy.t
or 'a Or_error.t
Deferred.t Lazy.t
, because there is a difference in power with these types. Any value of type 'a Deferred.t Lazy.t
would mishandle asynchronous exceptions in the computation of 'a
. For instance, the following code blocks forever regardless of how v
is defined:
let v : Nothing.t Deferred.t Lazy.t = lazy (return "" >>| failwith) in
let%bind _ = try_with (fun () -> force v) in
let%bind _ = try_with (fun () -> force v) in
There is no val of_lazy : 'a Deferred.t Lazy.t -> 'a t
because of the difference in power.
See also Deferred.Memo.unit
, if you only are interested in create
and force
.
type 'a t
val create : (unit -> 'a Async_kernel.Deferred.t ) -> 'a t
create f
creates a new lazy deferred that will call f
when it is forced.
val force : 'a t -> 'a Core_kernel.Or_error.t Async_kernel.Deferred.t
force t
forces evaluation of t
and returns a deferred that becomes determined when the deferred computation becomes determined or raises.
val force_exn : 'a t -> 'a Async_kernel.Deferred.t
val wait : 'a t -> 'a Core_kernel.Or_error.t Async_kernel.Deferred.t
wait t
and wait_exn t
waits for t
to be forced. If no one ever calls force t
, they will wait forever.
val wait_exn : 'a t -> 'a Async_kernel.Deferred.t
bind t f
in the lazy-deferred monad creates a computation that, when forced, will force t
, apply f
to the result, and then force the result of that.
include Core_kernel.Monad with type 'a t := 'a t
type 'a t
include Base__.Monad_intf.S_without_syntax with type 'a t := 'a t
type 'a t
include Base__.Monad_intf.Infix with type 'a t := 'a t
type 'a t
val (>>=) : 'a t -> ('a -> 'b t ) -> 'b t
t >>= f
returns a computation that sequences the computations represented by two monad elements. The resulting computation first does t
to yield a value v
, and then runs the computation returned by f v
.
val (>>|) : 'a t -> ('a -> 'b ) -> 'b t
t >>| f
is t >>= (fun a -> return (f a))
.
val bind : 'a t -> f:('a -> 'b t ) -> 'b t
bind t ~f
= t >>= f
val return : 'a -> 'a t
return v
returns the (trivial) computation that returns v.
val map : 'a t -> f:('a -> 'b ) -> 'b t
map t ~f
is t >>| f.
val join : 'a t t -> 'a t
join t
is t >>= (fun t' -> t')
.
val ignore_m : 'a t -> unit t
ignore_m t
is map t ~f:(fun _ -> ())
. ignore_m
used to be called ignore
, but we decided that was a bad name, because it shadowed the widely used Caml.ignore
. Some monads still do let ignore = ignore_m
for historical reasons.
val all : 'a t list -> 'a list t
val all_unit : unit t list -> unit t
Like all
, but ensures that every monadic value in the list produces a unit value, all of which are discarded rather than being collected into a list.
val bind' : 'a t -> ('a -> 'b Async_kernel.Deferred.t ) -> 'b t
bind'
differs from bind
in that the supplied function produces an 'a Deferred.t
rather than an 'a t
.
val peek : 'a t -> 'a Core_kernel.Or_error.t option
peek t = Deferred.peek (wait t)
val peek_exn : 'a t -> 'a option
val is_determined : _ t -> bool
val is_forced : _ t -> bool