package travesty

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package travesty
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S1 is the signature of a monadic traversal over arity-1 types.

type 'a t

The type of the container to map over.

S1s can traverse: when the container type is 'a t, the element type is 'a.

include Generic with type 'a t := 'a t and type 'a elt := '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 Types_intf.Generic with type 'a t := 'a t with type 'a elt := 'a
module M : Base.Monad.S

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

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:

(* 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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