With_errors specialises On_monad to the error monad.
include Generic
with type 'a t := Elt.t I.t
with type 'a elt := Elt.t
with module M := Base.Or_errorGeneric 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.
val map_m :
Elt.t I.t ->
f:(Elt.t -> Elt.t Base.Or_error.t) ->
Elt.t I.t Base.Or_error.tmap_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 ~fval fold_map_m :
Elt.t I.t ->
f:('acc -> Elt.t -> ('acc * Elt.t) Base.Or_error.t) ->
init:'acc ->
('acc * Elt.t I.t) Base.Or_error.tfold_map_m c ~f ~init folds f monadically over every t in c, threading through an accumulator with initial value init.
val fold_m :
Elt.t I.t ->
init:'acc ->
f:('acc -> Elt.t -> 'acc Base.Or_error.t) ->
'acc Base.Or_error.tfold_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 :
Elt.t I.t ->
f:(Elt.t -> Base.unit Base.Or_error.t) ->
Base.unit Base.Or_error.titer_m x ~f iterates the monadic computation f over x, returning the final monadic effect.
val mapi_m :
f:(Base.int -> Elt.t -> Elt.t Base.Or_error.t) ->
Elt.t I.t ->
Elt.t I.t Base.Or_error.tmapi_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.