package travesty

Utility functions for building traversals.

Parameters

Signature

Variants

Functions beginning proc_variant are useful for building traversable containers on top of Variantslib's map function.

Here's an example where we define a generic traversal function over a variant type using proc_variant1 and proc_variant3, then use it to build a traversable container instance for inspecting and modifying a specific type of data regardless of variant.

(* This type describes x86 operands: *)
type t =
  | Location of Location.t
  | Immediate of Disp.t
  | String of string
  | Typ of string
  | Bop of t * operator * t [@@deriving variants]

(* We use the helpers to build an intermediate mapper... *)
module Base_map (M : Monad.S) = struct
  module F = Travesty.Traversable.Helpers (M)

  let rec map_m (x : t) ~location ~immediate ~string ~typ ~bop
    : t M.t =
    Variants.map x
      ~location:(F.proc_variant1 location)
      ~immediate:(F.proc_variant1 immediate)
      ~string:(F.proc_variant1 string)
      ~typ:(F.proc_variant1 typ)
      (* Note that this recursively folds down the operands,
         and that the [bop] function only receives the operator. *)
      ~bop:(F.proc_variant3 (fun (l, b, r) ->
          let open M.Let_syntax in
          let%bind l' = map_m ~location ~immediate ~string ~typ ~bop l in
          let%bind b' = bop b in
          let%map  r' = map_m ~location ~immediate ~string ~typ ~bop r in
          (l', b', r')))
  ;;
end

(* ...then use it to build a traversable container over all of
   the symbols in an operand. *)
module On_symbols
  : Travesty.Traversable.S0_container with type t := t
                                       and type elt := string =
  Travesty.Traversable.Make_container0 (struct
    type nonrec t = t
    module Elt = String

    module On_monad (M : Monad.S) = struct
      module B = Base_map (M)
      (* Recursively using other traversables: *)
      module L = Location.On_symbols.On_monad (M)
      module D = Disp.On_symbols.On_monad (M)

      let map_m t ~f =
        B.map_m t
          ~location:(L.map_m ~f)
          ~immediate:(D.map_m ~f)
          (* These don't contain symbols: *)
          ~string:M.return
          ~typ:M.return
          ~bop:M.return
    end
  end)

Fields

The function proc_field is useful for building traversable containers on top of Fieldslib's fold function.

Here's an example where we define a generic traversal function over a record type using proc_field, then use it to build a traversable container instance for inspecting and modifying a specific type of data inside the record.

(* Type for holding x86 memory references. *)
type t =
  { seg    : Reg.t   option (* segment register *)
  ; disp   : Disp.t  option (* displacement *)
  ; base   : Reg.t   option (* base register *)
  ; index  : Index.t option (* index *)
  } [@@deriving fields]

(* First, build a generic traversal function (this isn't,
   itself, a Traversable)... *)
module Base_map (M : Monad.S) = struct
  module F = Travesty.Traversable.Helpers (M)
  let map_m indirect ~seg ~disp ~base ~index =
    Fields.fold
      ~init:(M.return indirect)
      ~seg:(F.proc_field seg)
      ~disp:(F.proc_field disp)
      ~base:(F.proc_field base)
      ~index:(F.proc_field index)
end

(* Now, we can build a traversable container instance.
     This one extracts symbols from memory references. *)
module On_symbols
  : Travesty.Traversable.S0_container with type t := t
                                       and type elt := string =
  Travesty.Traversable.Make_container0 (struct
    type nonrec t = t
    module Elt = String
    module Set = String.Set

    module On_monad (M : Monad.S) = struct
      module B = Base_map (M)
      module D = Disp.On_symbols.On_monad (M)
      module O = My_option.On_monad (M)

      let map_m t ~f =
        B.map_m t
          (* Chained monadic traversal. *)
          ~disp:(O.map_m ~f:(D.map_m ~f))
          (* Segments, bases, and indices have no symbols. *)
          ~seg:M.return
          ~base:M.return
          ~index:M.return
    end
  end)