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