Traversable_types.Basic_generic_on_applicative
Basic_generic_on_applicative
describes traversal on either an arity-0 or arity-1 type.
'a t
becomes t
and 'a elt
becomes elt
.'a t
becomes 'a t
and 'a elt
becomes 'a
.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 Generic_types.Generic
map_m c ~f
maps f
over every t
in c
, threading through an applicative functor.
Example:
(* Travesty_base_exts.List adds applicative traversals to a list;
With_errors (in S1_container) implements them on the On_error
applicative functor. *)
let f x =
Or_error.(if 0 < x then error_string "negative!" else ok x)
in
List.With_errors.map_m integers ~f