package travesty
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On_monad implements monadic traversal for a given monad M.

Parameters

module M : Base.Monad.S

Signature

include Types_intf.S0 with type t := t with type elt := Elt.t
include Basic_generic_on_monad with type 'a t := t and type 'a elt := Elt.t with module M := M

Generic refers to the container type as 'a t, and the element type as 'a elt; substitute t/elt (arity-0) or 'a t/'a (arity-1) accordingly below.

include Types_intf.Generic with type 'a t := t with type 'a elt := Elt.t
val map_m : t -> f:(Elt.t -> Elt.t M.t) -> t M.t

map_m c ~f maps f over every t in c, threading through monadic state.

Example:

(* Travesty_base_exts.List adds monadic traversals to a list;
   With_errors (in S1_container) implements them on the On_error
   monad. *)

let f x =
  Or_error.(if 0 < x then error_string "negative!" else ok x)
in
List.With_errors.map_m integers ~f