Travesty_base_exts.Or_error
Or-error monad extensions.
This module contains various extensions for Base
's Or_error
monad, including monadic traversal over successful values and monad extensions.
Defined to let this module be used directly in chaining operations etc.
Monad extensions for Or_error
.
include Travesty.Monad_exts_types.S with type 'a t := 'a t
S
subsumes S_let
.
then_m x y
sequentially composes the actions x
and y
as with >>=
, but, rather than using the returned value of x
, it instead just returns y
.
compose_m f g
is the Kleisli composition of f
and g
.
map_when_m ?otherwise condition ~f a
is f a
when condition
is true, and otherwise a
(by default, return
) otherwise.
when_m ?otherwise condition ~f
is f ()
when condition
is true, and otherwise ()
(by default, return
) otherwise.
map_unless_m ?otherwise condition ~f a
is f a
when condition
is false, and otherwise a
(by default, return
) otherwise.
unless_m ?otherwise condition ~f
is f ()
when condition
is false, and otherwise ()
(by default, return
) otherwise.
tee_m val ~f
executes f val
for its monadic action, then returns val
.
Example (using an extended Or_error):
let fail_if_negative x =
On_error.when_m (Int.is_negative x) ~f:(fun () ->
Or_error.error_string "value is negative!" )
in
Or_error.(42 |> tee_m ~f:fail_if_negative >>| fun x -> x * x)
(* Ok (1764) *)
val tee : 'a -> f:('a -> unit) -> 'a t
tee val ~f
behaves as tee_m
, but takes a non-monadic f
.
Example (using an extended Or_error):
let print_if_negative x =
if Int.negative x then Stdio.print_string "value is negative!"
in
Or_error.(
try_get_value () >>= tee ~f:print_if_negative >>= try_use_value () )
Or_error
is a bi-traversable type, with the right type fixed to Error.t
. (This is backwards from Haskell conventions, but matches the position Error.t
takes in Result
in Base
.
include Travesty.Bi_traversable_types.S1_left
with type 'l t := 'l t
and type right = Base.Error.t
include Travesty.Generic_types.Bi_left
with type 'l t := 'l t
with type right = Base.Error.t
include Travesty.Bi_traversable_types.Generic
with type ('l, 'r) t := 'l t
and type 'l left := 'l
and type 'r right := right
We can do non-monadic bi-mapping operations.
module On
(M : Base.Applicative.S) :
Travesty.Bi_traversable_types.Generic_on_applicative
with type ('l, 'r) t := 'l t
and type 'l left := 'l
and type 'r right := right
and module M := M
On
implements bi-traversal operators for a given applicative functor M
.
module On_monad
(M : Base.Monad.S) :
Travesty.Bi_traversable_types.Generic_on_applicative
with type ('l, 'r) t := 'l t
and type 'l left := 'l
and type 'r right := right
and module M := Travesty.Monad_exts.App(M)
On_monad
implements bi-traversal operators for a given monad M
.
module On_ok : Travesty.Traversable_types.S1 with type 'a t = 'a t
On_ok
is shorthand for Traverse1_left
on this module.
These functions are just shorthand for mapping over a list, then using the various combine_errors
functions in Base.
Prefer using these, where possible, over the analogous functions in T_list.With_errors; these ones correctly merge errors.
combine_map xs ~f
is short for map xs ~f
followed by combine_errors
.