From e6af95f2b2a5a7012cbcc3c950823982d074f095 Mon Sep 17 00:00:00 2001 From: c-cube Date: Fri, 2 May 2025 15:01:11 +0000 Subject: [PATCH] deploy: bb9418d86afebf19438d64b96e51da25f7d90e98 --- moonpool/Moonpool/Blocking_queue/index.html | 30 ++++++++++----------- moonpool/Moonpool/Fut/index.html | 4 +-- 2 files changed, 17 insertions(+), 17 deletions(-) diff --git a/moonpool/Moonpool/Blocking_queue/index.html b/moonpool/Moonpool/Blocking_queue/index.html index 2b7c2c44..2ef85651 100644 --- a/moonpool/Moonpool/Blocking_queue/index.html +++ b/moonpool/Moonpool/Blocking_queue/index.html @@ -1,17 +1,17 @@ -Blocking_queue (moonpool.Moonpool.Blocking_queue)

Module Moonpool.Blocking_queue

A simple blocking queue.

This queue is quite basic and will not behave well under heavy contention. However, it can be sufficient for many practical use cases.

NOTE: this queue will typically block the caller thread in case the operation (push/pop) cannot proceed. Be wary of deadlocks when using the queue from a pool when you expect the other end to also be produced/consumed from the same pool.

See discussion on Fut.wait_block for more details on deadlocks and how to mitigate the risk of running into them.

More scalable queues can be found in Lockfree (https://github.com/ocaml-multicore/lockfree/)

type 'a t

Unbounded blocking queue.

This queue is thread-safe and will block when calling pop on it when it's empty.

val create : unit -> _ t

Create a new unbounded queue.

val size : _ t -> int

Number of items currently in the queue. Note that pop might still block if this returns a non-zero number, since another thread might have consumed the items in the mean time.

  • since 0.2
exception Closed
val push : 'a t -> 'a -> unit

push q x pushes x into q, and returns ().

In the current implementation, push q will never block for a long time, it will only block while waiting for a lock so it can push the element.

  • raises Closed

    if the queue is closed (by a previous call to close q)

val pop : 'a t -> 'a

pop q pops the next element in q. It might block until an element comes.

  • raises Closed

    if the queue was closed before a new element was available.

val close : _ t -> unit

Close the queue, meaning there won't be any more push allowed, ie push will raise Closed.

pop will keep working and will return the elements present in the queue, until it's entirely drained; then pop will also raise Closed.

val try_pop : force_lock:bool -> 'a t -> 'a option

try_pop q immediately pops the first element of q, if any, or returns None without blocking.

  • parameter force_lock

    if true, use Mutex.lock (which can block under contention); if false, use Mutex.try_lock, which might return None even in presence of an element if there's contention

val try_push : 'a t -> 'a -> bool

try_push q x tries to push into q, in which case it returns true; or it fails to push and returns false without blocking.

  • raises Closed

    if the locking succeeded but the queue is closed.

val transfer : 'a t -> 'a Stdlib.Queue.t -> unit

transfer bq q2 transfers all items presently in bq into q2 in one atomic section, and clears bq. It blocks if no element is in bq.

This is useful to consume elements from the queue in batch. Create a Queue.t locally:

let dowork (work_queue: job Bb_queue.t) =
-  (* local queue, not thread safe *)
-  let local_q = Queue.create() in
-  try
-    while true do
-      (* work on local events, already on this thread *)
-      while not (Queue.is_empty local_q) do
-        let job = Queue.pop local_q in
-        process_job job
-      done;
+Blocking_queue (moonpool.Moonpool.Blocking_queue)
Module Moonpool.Blocking_queue
A simple blocking queue.
This queue is quite basic and will not behave well under heavy contention. However, it can be sufficient for many practical use cases.
NOTE: this queue will typically block the caller thread in case the operation (push/pop) cannot proceed. Be wary of deadlocks when using the queue from a pool when you expect the other end to also be produced/consumed from the same pool.
See discussion on Fut.wait_block for more details on deadlocks and how to mitigate the risk of running into them.
More scalable queues can be found in Lockfree (https://github.com/ocaml-multicore/lockfree/)
type 'a t
Unbounded blocking queue.
This queue is thread-safe and will block when calling pop on it when it's empty.
val create : unit -> _ t
Create a new unbounded queue.
val size : _ t -> int
Number of items currently in the queue. Note that pop might still block if this returns a non-zero number, since another thread might have consumed the items in the mean time.
  • since 0.2
exception Closed
val push : 'a t -> 'a -> unit
push q x pushes x into q, and returns ().
In the current implementation, push q will never block for a long time, it will only block while waiting for a lock so it can push the element.
  • raises Closed 
    if the queue is closed (by a previous call to close q)
val pop : 'a t -> 'a
pop q pops the next element in q. It might block until an element comes.
  • raises Closed 
    if the queue was closed before a new element was available.
val close : _ t -> unit
Close the queue, meaning there won't be any more push allowed, ie push will raise Closed.
pop will keep working and will return the elements present in the queue, until it's entirely drained; then pop will also raise Closed.
val try_pop : force_lock:bool -> 'a t -> 'a option
try_pop q immediately pops the first element of q, if any, or returns None without blocking.
  • parameter force_lock 
    if true, use Mutex.lock (which can block under contention); if false, use Mutex.try_lock, which might return None even in presence of an element if there's contention
val try_push : 'a t -> 'a -> bool
try_push q x tries to push into q, in which case it returns true; or it fails to push and returns false without blocking.
  • raises Closed 
    if the locking succeeded but the queue is closed.
val transfer : 'a t -> 'a Stdlib.Queue.t -> unit
transfer bq q2 transfers all items presently in bq into q2 in one atomic section, and clears bq. It blocks if no element is in bq.
This is useful to consume elements from the queue in batch. Create a Queue.t locally:
  let dowork (work_queue : job Bb_queue.t) =
+    (* local queue, not thread safe *)
+    let local_q = Queue.create () in
+    try
+      while true do
+        (* work on local events, already on this thread *)
+        while not (Queue.is_empty local_q) do
+          let job = Queue.pop local_q in
+          process_job job
+        done;
 
-      (* get all the events in the incoming blocking queue, in
-         one single critical section. *)
-      Bb_queue.transfer work_queue local_q
-    done
-  with Bb_queue.Closed -> ()
  • since 0.4
type 'a gen = unit -> 'a option
type 'a iter = ('a -> unit) -> unit
val to_iter : 'a t -> 'a iter
to_iter q returns an iterator over all items in the queue. This might not terminate if q is never closed.
  • since 0.4
val to_gen : 'a t -> 'a gen
to_gen q returns a generator from the queue.
  • since 0.4
val to_seq : 'a t -> 'a Stdlib.Seq.t
to_gen q returns a (transient) sequence from the queue.
  • since 0.4

+        (* get all the events in the incoming blocking queue, in
+           one single critical section. *)
+        Bb_queue.transfer work_queue local_q
+      done
+    with Bb_queue.Closed -> ()
  • since 0.4
type 'a gen = unit -> 'a option
type 'a iter = ('a -> unit) -> unit
val to_iter : 'a t -> 'a iter

to_iter q returns an iterator over all items in the queue. This might not terminate if q is never closed.

  • since 0.4
val to_gen : 'a t -> 'a gen

to_gen q returns a generator from the queue.

  • since 0.4
val to_seq : 'a t -> 'a Stdlib.Seq.t

to_gen q returns a (transient) sequence from the queue.

  • since 0.4
diff --git a/moonpool/Moonpool/Fut/index.html b/moonpool/Moonpool/Fut/index.html index 3a120416..f21800e0 100644 --- a/moonpool/Moonpool/Fut/index.html +++ b/moonpool/Moonpool/Fut/index.html @@ -1,3 +1,3 @@ -Fut (moonpool.Moonpool.Fut)

Module Moonpool.Fut

Futures.

A future of type 'a t represents the result of a computation that will yield a value of type 'a.

Typically, the computation is running on a thread pool Runner.t and will proceed on some worker. Once set, a future cannot change. It either succeeds (storing a Ok x with x: 'a), or fail (storing a Error (exn, bt) with an exception and the corresponding backtrace).

Combinators such as map and join_array can be used to produce futures from other futures (in a monadic way). Some combinators take a on argument to specify a runner on which the intermediate computation takes place; for example map ~on:pool ~f fut maps the value in fut using function f, applicatively; the call to f happens on the runner pool (once fut resolves successfully with a value).

type 'a or_error = ('a, Exn_bt.t) result
type 'a t = 'a Picos.Computation.t

A future with a result of type 'a.

type 'a promise = private 'a t

A promise, which can be fulfilled exactly once to set the corresponding future. This is a private alias of 'a t since 0.7, previously it was opaque.

val make : unit -> 'a t * 'a promise

Make a new future with the associated promise.

val make_promise : unit -> 'a promise

Same as make but returns a single promise (which can be upcast to a future). This is useful mostly to preserve memory.

How to upcast to a future in the worst case:

let prom = Fut.make_promise();;
-  let fut = (prom : _ Fut.promise :> _ Fut.t) ;;
  • since 0.7
val on_result : 'a t -> ('a or_error -> unit) -> unit

on_result fut f registers f to be called in the future when fut is set ; or calls f immediately if fut is already set.

val on_result_ignore : _ t -> (Exn_bt.t option -> unit) -> unit

on_result_ignore fut f registers f to be called in the future when fut is set; or calls f immediately if fut is already set. It does not pass the result, only a success/error signal.

  • since 0.7
exception Already_fulfilled
val fulfill : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time.

val fulfill_idempotent : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time. Does nothing if the promise is already fulfilled.

val return : 'a -> 'a t

Already settled future, with a result

val fail : exn -> Stdlib.Printexc.raw_backtrace -> _ t

Already settled future, with a failure

val fail_exn_bt : Exn_bt.t -> _ t

Fail from a bundle of exception and backtrace

  • since 0.6
val of_result : 'a or_error -> 'a t
val is_resolved : _ t -> bool

is_resolved fut is true iff fut is resolved.

val peek : 'a t -> 'a or_error option

peek fut returns Some r if fut is currently resolved with r, and None if fut is not resolved yet.

exception Not_ready
  • since 0.2
val get_or_fail : 'a t -> 'a or_error

get_or_fail fut obtains the result from fut if it's fulfilled (i.e. if peek fut returns Some res, get_or_fail fut returns res).

  • since 0.2
val get_or_fail_exn : 'a t -> 'a

get_or_fail_exn fut obtains the result from fut if it's fulfilled, like get_or_fail. If the result is an Error _, the exception inside is re-raised.

  • since 0.2
val is_done : _ t -> bool

Is the future resolved? This is the same as peek fut |> Option.is_some.

  • since 0.2
val is_success : _ t -> bool

Checks if the future is resolved with Ok _ as a result.

  • since 0.6
val is_failed : _ t -> bool

Checks if the future is resolved with Error _ as a result.

  • since 0.6
val raise_if_failed : _ t -> unit

raise_if_failed fut raises e if fut failed with e.

  • since 0.6

Combinators

val spawn : on:Runner.t -> (unit -> 'a) -> 'a t

spaw ~on f runs f() on the given runner on, and return a future that will hold its result.

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

This must be run from inside a runner, and schedules the new task on it as well.

See Runner.get_current_runner to see how the runner is found.

  • since 0.5
  • raises Failure

    if run from outside a runner.

val reify_error : 'a t -> 'a or_error t

reify_error fut turns a failing future into a non-failing one that contain Error (exn, bt). A non-failing future returning x is turned into Ok x

  • since 0.4
val map : ?on:Runner.t -> f:('a -> 'b) -> 'a t -> 'b t

map ?on ~f fut returns a new future fut2 that resolves with f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val bind : ?on:Runner.t -> f:('a -> 'b t) -> 'a t -> 'b t

bind ?on ~f fut returns a new future fut2 that resolves like the future f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val bind_reify_error : ?on:Runner.t -> f:('a or_error -> 'b t) -> 'a t -> 'b t

bind_reify_error ?on ~f fut returns a new future fut2 that resolves like the future f (Ok x) if fut resolved with x; and resolves like the future f (Error (exn, bt)) if fut fails with exn and backtrace bt.

  • parameter on

    if provided, f runs on the given runner

  • since 0.4
val join : 'a t t -> 'a t

join fut is fut >>= Fun.id. It joins the inner layer of the future.

  • since 0.2
val both : 'a t -> 'b t -> ('a * 'b) t

both a b succeeds with x, y if a succeeds with x and b succeeds with y, or fails if any of them fails.

val choose : 'a t -> 'b t -> ('a, 'b) Either.t t

choose a b succeeds Left x or Right y if a succeeds with x or b succeeds with y, or fails if both of them fails. If they both succeed, it is not specified which result is used.

val choose_same : 'a t -> 'a t -> 'a t

choose_same a b succeeds with the value of one of a or b if they succeed, or fails if both fail. If they both succeed, it is not specified which result is used.

val join_array : 'a t array -> 'a array t

Wait for all the futures in the array. Fails if any future fails.

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

Wait for all the futures in the list. Fails if any future fails.

module Advanced : sig ... end
val map_list : f:('a -> 'b t) -> 'a list -> 'b list t

map_list ~f l is like join_list @@ List.map f l.

  • since 0.5.1
val wait_array : _ t array -> unit t

wait_array arr waits for all futures in arr to resolve. It discards the individual results of futures in arr. It fails if any future fails.

val wait_list : _ t list -> unit t

wait_list l waits for all futures in l to resolve. It discards the individual results of futures in l. It fails if any future fails.

val for_ : on:Runner.t -> int -> (int -> unit) -> unit t

for_ ~on n f runs f 0, f 1, …, f (n-1) on the runner, and returns a future that resolves when all the tasks have resolved, or fails as soon as one task has failed.

val for_array : on:Runner.t -> 'a array -> (int -> 'a -> unit) -> unit t

for_array ~on arr f runs f 0 arr.(0), …, f (n-1) arr.(n-1) in the runner (where n = Array.length arr), and returns a future that resolves when all the tasks are done, or fails if any of them fails.

  • since 0.2
val for_list : on:Runner.t -> 'a list -> ('a -> unit) -> unit t

for_list ~on l f is like for_array ~on (Array.of_list l) f.

  • since 0.2

Await

NOTE This is only available on OCaml 5.

val await : 'a t -> 'a

await fut suspends the current tasks until fut is fulfilled, then resumes the task on this same runner (but possibly on a different thread/domain).

  • since 0.3

This must only be run from inside the runner itself. The runner must support Suspend_. NOTE: only on OCaml 5.x

Blocking

val wait_block : 'a t -> 'a or_error

wait_block fut blocks the current thread until fut is resolved, and returns its value.

NOTE: A word of warning: this will monopolize the calling thread until the future resolves. This can also easily cause deadlocks, if enough threads in a pool call wait_block on futures running on the same pool or a pool depending on it.

A good rule to avoid deadlocks is to run this from outside of any pool, or to have an acyclic order between pools where wait_block is only called from a pool on futures evaluated in a pool that comes lower in the hierarchy. If this rule is broken, it is possible for all threads in a pool to wait for futures that can only make progress on these same threads, hence the deadlock.

val wait_block_exn : 'a t -> 'a

Same as wait_block but re-raises the exception if the future failed.

Infix operators

These combinators run on either the current pool (if present), or on the same thread that just fulfilled the previous future if not.

They were previously present as module Infix_local and val infix, but are now simplified.

module Infix : sig ... end
include module type of Infix
val (>|=) : 'a t -> ('a -> 'b) -> 'b t
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
val (let+) : 'a t -> ('a -> 'b) -> 'b t
val (and+) : 'a t -> 'b t -> ('a * 'b) t
val (let*) : 'a t -> ('a -> 'b t) -> 'b t
val (and*) : 'a t -> 'b t -> ('a * 'b) t
module Infix_local = Infix
+Fut (moonpool.Moonpool.Fut)

Module Moonpool.Fut

Futures.

A future of type 'a t represents the result of a computation that will yield a value of type 'a.

Typically, the computation is running on a thread pool Runner.t and will proceed on some worker. Once set, a future cannot change. It either succeeds (storing a Ok x with x: 'a), or fail (storing a Error (exn, bt) with an exception and the corresponding backtrace).

Combinators such as map and join_array can be used to produce futures from other futures (in a monadic way). Some combinators take a on argument to specify a runner on which the intermediate computation takes place; for example map ~on:pool ~f fut maps the value in fut using function f, applicatively; the call to f happens on the runner pool (once fut resolves successfully with a value).

type 'a or_error = ('a, Exn_bt.t) result
type 'a t = 'a Picos.Computation.t

A future with a result of type 'a.

type 'a promise = private 'a t

A promise, which can be fulfilled exactly once to set the corresponding future. This is a private alias of 'a t since 0.7, previously it was opaque.

val make : unit -> 'a t * 'a promise

Make a new future with the associated promise.

val make_promise : unit -> 'a promise

Same as make but returns a single promise (which can be upcast to a future). This is useful mostly to preserve memory.

How to upcast to a future in the worst case:

  let prom = Fut.make_promise ()
+  let fut = (prom : _ Fut.promise :> _ Fut.t)
  • since 0.7
val on_result : 'a t -> ('a or_error -> unit) -> unit

on_result fut f registers f to be called in the future when fut is set ; or calls f immediately if fut is already set.

val on_result_ignore : _ t -> (Exn_bt.t option -> unit) -> unit

on_result_ignore fut f registers f to be called in the future when fut is set; or calls f immediately if fut is already set. It does not pass the result, only a success/error signal.

  • since 0.7
exception Already_fulfilled
val fulfill : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time.

val fulfill_idempotent : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time. Does nothing if the promise is already fulfilled.

val return : 'a -> 'a t

Already settled future, with a result

val fail : exn -> Stdlib.Printexc.raw_backtrace -> _ t

Already settled future, with a failure

val fail_exn_bt : Exn_bt.t -> _ t

Fail from a bundle of exception and backtrace

  • since 0.6
val of_result : 'a or_error -> 'a t
val is_resolved : _ t -> bool

is_resolved fut is true iff fut is resolved.

val peek : 'a t -> 'a or_error option

peek fut returns Some r if fut is currently resolved with r, and None if fut is not resolved yet.

exception Not_ready
  • since 0.2
val get_or_fail : 'a t -> 'a or_error

get_or_fail fut obtains the result from fut if it's fulfilled (i.e. if peek fut returns Some res, get_or_fail fut returns res).

  • since 0.2
val get_or_fail_exn : 'a t -> 'a

get_or_fail_exn fut obtains the result from fut if it's fulfilled, like get_or_fail. If the result is an Error _, the exception inside is re-raised.

  • since 0.2
val is_done : _ t -> bool

Is the future resolved? This is the same as peek fut |> Option.is_some.

  • since 0.2
val is_success : _ t -> bool

Checks if the future is resolved with Ok _ as a result.

  • since 0.6
val is_failed : _ t -> bool

Checks if the future is resolved with Error _ as a result.

  • since 0.6
val raise_if_failed : _ t -> unit

raise_if_failed fut raises e if fut failed with e.

  • since 0.6

Combinators

val spawn : on:Runner.t -> (unit -> 'a) -> 'a t

spaw ~on f runs f() on the given runner on, and return a future that will hold its result.

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

This must be run from inside a runner, and schedules the new task on it as well.

See Runner.get_current_runner to see how the runner is found.

  • since 0.5
  • raises Failure

    if run from outside a runner.

val reify_error : 'a t -> 'a or_error t

reify_error fut turns a failing future into a non-failing one that contain Error (exn, bt). A non-failing future returning x is turned into Ok x

  • since 0.4
val map : ?on:Runner.t -> f:('a -> 'b) -> 'a t -> 'b t

map ?on ~f fut returns a new future fut2 that resolves with f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val bind : ?on:Runner.t -> f:('a -> 'b t) -> 'a t -> 'b t

bind ?on ~f fut returns a new future fut2 that resolves like the future f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val bind_reify_error : ?on:Runner.t -> f:('a or_error -> 'b t) -> 'a t -> 'b t

bind_reify_error ?on ~f fut returns a new future fut2 that resolves like the future f (Ok x) if fut resolved with x; and resolves like the future f (Error (exn, bt)) if fut fails with exn and backtrace bt.

  • parameter on

    if provided, f runs on the given runner

  • since 0.4
val join : 'a t t -> 'a t

join fut is fut >>= Fun.id. It joins the inner layer of the future.

  • since 0.2
val both : 'a t -> 'b t -> ('a * 'b) t

both a b succeeds with x, y if a succeeds with x and b succeeds with y, or fails if any of them fails.

val choose : 'a t -> 'b t -> ('a, 'b) Either.t t

choose a b succeeds Left x or Right y if a succeeds with x or b succeeds with y, or fails if both of them fails. If they both succeed, it is not specified which result is used.

val choose_same : 'a t -> 'a t -> 'a t

choose_same a b succeeds with the value of one of a or b if they succeed, or fails if both fail. If they both succeed, it is not specified which result is used.

val join_array : 'a t array -> 'a array t

Wait for all the futures in the array. Fails if any future fails.

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

Wait for all the futures in the list. Fails if any future fails.

module Advanced : sig ... end
val map_list : f:('a -> 'b t) -> 'a list -> 'b list t

map_list ~f l is like join_list @@ List.map f l.

  • since 0.5.1
val wait_array : _ t array -> unit t

wait_array arr waits for all futures in arr to resolve. It discards the individual results of futures in arr. It fails if any future fails.

val wait_list : _ t list -> unit t

wait_list l waits for all futures in l to resolve. It discards the individual results of futures in l. It fails if any future fails.

val for_ : on:Runner.t -> int -> (int -> unit) -> unit t

for_ ~on n f runs f 0, f 1, …, f (n-1) on the runner, and returns a future that resolves when all the tasks have resolved, or fails as soon as one task has failed.

val for_array : on:Runner.t -> 'a array -> (int -> 'a -> unit) -> unit t

for_array ~on arr f runs f 0 arr.(0), …, f (n-1) arr.(n-1) in the runner (where n = Array.length arr), and returns a future that resolves when all the tasks are done, or fails if any of them fails.

  • since 0.2
val for_list : on:Runner.t -> 'a list -> ('a -> unit) -> unit t

for_list ~on l f is like for_array ~on (Array.of_list l) f.

  • since 0.2

Await

NOTE This is only available on OCaml 5.

val await : 'a t -> 'a

await fut suspends the current tasks until fut is fulfilled, then resumes the task on this same runner (but possibly on a different thread/domain).

  • since 0.3

This must only be run from inside the runner itself. The runner must support Suspend_. NOTE: only on OCaml 5.x

Blocking

val wait_block : 'a t -> 'a or_error

wait_block fut blocks the current thread until fut is resolved, and returns its value.

NOTE: A word of warning: this will monopolize the calling thread until the future resolves. This can also easily cause deadlocks, if enough threads in a pool call wait_block on futures running on the same pool or a pool depending on it.

A good rule to avoid deadlocks is to run this from outside of any pool, or to have an acyclic order between pools where wait_block is only called from a pool on futures evaluated in a pool that comes lower in the hierarchy. If this rule is broken, it is possible for all threads in a pool to wait for futures that can only make progress on these same threads, hence the deadlock.

val wait_block_exn : 'a t -> 'a

Same as wait_block but re-raises the exception if the future failed.

Infix operators

These combinators run on either the current pool (if present), or on the same thread that just fulfilled the previous future if not.

They were previously present as module Infix_local and val infix, but are now simplified.

module Infix : sig ... end
include module type of Infix
val (>|=) : 'a t -> ('a -> 'b) -> 'b t
val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
val (let+) : 'a t -> ('a -> 'b) -> 'b t
val (and+) : 'a t -> 'b t -> ('a * 'b) t
val (let*) : 'a t -> ('a -> 'b t) -> 'b t
val (and*) : 'a t -> 'b t -> ('a * 'b) t
module Infix_local = Infix