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)