package travesty

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package travesty
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Generic describes monadic traversal on either an arity-0 or arity-1 type.

  • For arity-0 types, use S0: 'a t becomes t, and 'a elt becomes elt;
  • For arity-1 types, use S1: '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 Types_intf.Generic
type 'a t

Placeholder for the container type.

type 'a elt

Placeholder for the type of elements inside the container.

module M : Base.Monad.S

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

val map_m : 'a t -> f:('a elt -> 'b elt 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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