package travesty

  1. Overview
  2. Docs
package travesty
Legend:
Library
Module
Module type
Parameter
Class
Class type

Extend creates extensions for a Monad.S.

Parameters

module M : Base.Monad.S

Signature

S subsumes S_let.

include Monad_exts_types.S_let with type 'a t := 'a M.t
val let+ : 'a M.t -> ('a -> 'b) -> 'b M.t

let+ is map.

val let* : 'a M.t -> ('a -> 'b M.t) -> 'b M.t

let* is bind.

Haskell-style operators

val then_m : _ M.t -> 'a M.t -> 'a M.t

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.

val (>>) : _ M.t -> 'a M.t -> 'a M.t

x >> y is then_m x y.

val compose_m : ('a -> 'b M.t) -> ('b -> 'c M.t) -> 'a -> 'c M.t

compose_m f g is the Kleisli composition of f and g.

val (>=>) : ('a -> 'b M.t) -> ('b -> 'c M.t) -> 'a -> 'c M.t

x >=> y is compose_m x y.

Guarded monadic computations

val map_when_m : ?otherwise:('a -> 'a M.t) -> bool -> 'a -> f:('a -> 'a M.t) -> 'a M.t

map_when_m ?otherwise condition ~f a is f a when condition is true, and otherwise a (by default, return) otherwise.

val when_m : ?otherwise:(unit -> unit M.t) -> bool -> f:(unit -> unit M.t) -> unit M.t

when_m ?otherwise condition ~f is f () when condition is true, and otherwise () (by default, return) otherwise.

val map_unless_m : ?otherwise:('a -> 'a M.t) -> bool -> 'a -> f:('a -> 'a M.t) -> 'a M.t

map_unless_m ?otherwise condition ~f a is f a when condition is false, and otherwise a (by default, return) otherwise.

val unless_m : ?otherwise:(unit -> unit M.t) -> bool -> f:(unit -> unit M.t) -> unit M.t

unless_m ?otherwise condition ~f is f () when condition is false, and otherwise () (by default, return) otherwise.

Executing monadic effects in the middle of pipelines

val tee_m : 'a -> f:('a -> unit M.t) -> 'a M.t

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 M.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 ())
OCaml

Innovation. Community. Security.

GitHub Discord Twitter Peertube RSS
About
Changelog Releases Industrial Users Academic Users Why OCaml
Ecosystem
Packages Community Events OCaml Planet Jobs
Resources
Install OCaml Get Started Platform Tools Language Manual Standard Library API Books Exercises Papers OCaml Playground Logo
Policies
Carbon Footprint Governance Privacy Code of Conduct