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package travesty
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On_monad implements monadic folding and mapping operators for a given monad M, including arity-1 specific operators.

Parameters

module M : Base.Monad.S

Signature

include Generic_on_monad with type 'a t := 'a t and type 'a elt := 'a with module M := M
include Basic_generic_on_monad with type 'a t := 'a t with type 'a elt := 'a 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 := 'a t with type 'a elt := 'a
val map_m : 'a t -> f:('a -> 'b M.t) -> 'b 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
val fold_map_m : 'a t -> f:('acc -> 'a -> ('acc * 'b) M.t) -> init:'acc -> ('acc * 'b t) M.t

fold_map_m c ~f ~init folds f monadically over every t in c, threading through an accumulator with initial value init.

val fold_m : 'a t -> init:'acc -> f:('acc -> 'a -> 'acc M.t) -> 'acc M.t

fold_m x ~init ~f folds the monadic computation f over x, starting with initial value init, and returning the final value inside the monadic effect.

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

iter_m x ~f iterates the monadic computation f over x, returning the final monadic effect.

val mapi_m : f:(Base.int -> 'a -> 'b M.t) -> 'a t -> 'b t M.t

mapi_m ~f x behaves as mapM, but also supplies f with the index of the element. This index should match the actual position of the element in the container x.

val sequence_m : 'a M.t t -> 'a t M.t

sequence_m x lifts a container of monads x to a monad containing a container, by sequencing the monadic effects from left to right.