Module Core_kernel__.Only_in_test
This module can be used to safely expose functions and values in signatures that should only be used in unit tests.
Under the hood, 'a t = 'a Lazy.t
and the only thing that ever forces them is the force
function below which should only be called in unit tests.
For example, suppose in some module, type t
is actually an int
. You want to keep the type definition opaque, but use the underlying representation in unit tests. You could write in the ml:
let test_to_int t = Only_in_test.return t
let test_of_int n = Only_in_test.return n
You would then expose in the mli:
type t
val test_to_int : t -> int Only_in_test.t
val test_of_int : int -> t Only_in_test.t
Finally, if you have specific values that you might want to use in unit tests, but that have top-level side-effects or take too long to compute, you can delay the side-effects or computation until the unit tests are run by writing, e.g.:
let (test_special_value : t Only_in_test.t) =
Only_in_test.of_thunk (fun () -> factorial 100)
instead of
let (test_special_value : t Only_in_test.t) =
Only_in_test.return (factorial 100)
type 'a t
include Core_kernel__.Import.Monad.S 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 of_thunk : (Core_kernel__.Import.unit -> 'a ) -> 'a t
val force : 'a t -> 'a