package travesty

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package travesty
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S0 is the signature of a monadic traversal over arity-0 types.

include Types_intf.S0
type t

The container type.

type elt

The element type.

include Generic with type 'a t := t and type 'a elt := elt

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
module M : Base.Monad.S

M is the monad over which we're fold-mapping.

val map_m : t -> f:(elt -> elt M.t) -> t M.t

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

Example:

(* T_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
T_list.With_errors.map_m integers ~f
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