ocaml/parsing/ast_mapper.ml

(***********************************************************************)
(*                                                                     *)
(*                                OCaml                                *)
(*                                                                     *)
(*                        Alain Frisch, LexiFi                         *)
(*                                                                     *)
(*  Copyright 2012 Institut National de Recherche en Informatique et   *)
(*  en Automatique.  All rights reserved.  This file is distributed    *)
(*  under the terms of the Q Public License version 1.0.               *)
(*                                                                     *)
(***********************************************************************)

(* A generic Parsetree mapping class *)

open Location
open Config
open Parsetree
open Asttypes

(* First, some helpers to build AST fragments *)

let map_snd f (x, y) = (x, f y)
let map_tuple f1 f2 (x, y) = (f1 x, f2 y)
let map_tuple3 f1 f2 f3 (x, y, z) = (f1 x, f2 y, f3 z)
let map_opt f = function None -> None | Some x -> Some (f x)

let map_loc sub {loc; txt} = {loc = sub # location loc; txt}
let map_attributes sub attrs = List.map (sub # attribute) attrs

module T = struct
  (* Type expressions for the core language *)

  let mk ?(loc = Location.none) x = {ptyp_desc = x; ptyp_loc = loc}
  let any ?loc () = mk ?loc Ptyp_any
  let var ?loc a = mk ?loc (Ptyp_var a)
  let arrow ?loc a b c = mk ?loc (Ptyp_arrow (a, b, c))
  let tuple ?loc a = mk ?loc (Ptyp_tuple a)
  let constr ?loc a b = mk ?loc (Ptyp_constr (a, b))
  let object_ ?loc a = mk ?loc (Ptyp_object a)
  let class_ ?loc a b c = mk ?loc (Ptyp_class (a, b, c))
  let alias ?loc a b = mk ?loc (Ptyp_alias (a, b))
  let variant ?loc a b c = mk ?loc (Ptyp_variant (a, b, c))
  let poly ?loc a b = mk ?loc (Ptyp_poly (a, b))
  let package ?loc a b = mk ?loc (Ptyp_package (a, b))
  let attribute ?loc a b = mk ?loc (Ptyp_attribute (a, b))
  let extension ?loc a = mk ?loc (Ptyp_extension a)

  let field_type ?(loc = Location.none) x = {pfield_desc = x; pfield_loc = loc}
  let field ?loc s t =
    let t =
      (* The type-checker expects the field to be a Ptyp_poly. Maybe
         it should wrap the type automatically... *)
      match t.ptyp_desc with
      | Ptyp_poly _ -> t
      | _ -> poly ?loc [] t
    in
    field_type ?loc (Pfield (s, t))
  let field_var ?loc () = field_type ?loc Pfield_var

  let core_field_type sub {pfield_desc = desc; pfield_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Pfield (s, d) -> field ~loc:(sub # location loc) s (sub # typ d)
    | Pfield_var -> field_var ~loc ()

  let row_field sub = function
    | Rtag (l, b, tl) -> Rtag (l, b, List.map (sub # typ) tl)
    | Rinherit t -> Rinherit (sub # typ t)

  let map sub {ptyp_desc = desc; ptyp_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Ptyp_any -> any ~loc ()
    | Ptyp_var s -> var ~loc s
    | Ptyp_arrow (lab, t1, t2) -> arrow ~loc lab (sub # typ t1) (sub # typ t2)
    | Ptyp_tuple tyl -> tuple ~loc (List.map (sub # typ) tyl)
    | Ptyp_constr (lid, tl) -> constr ~loc (map_loc sub lid) (List.map (sub # typ) tl)
    | Ptyp_object l -> object_ ~loc (List.map (core_field_type sub) l)
    | Ptyp_class (lid, tl, ll) -> class_ ~loc (map_loc sub lid) (List.map (sub # typ) tl) ll
    | Ptyp_alias (t, s) -> alias ~loc (sub # typ t) s
    | Ptyp_variant (rl, b, ll) -> variant ~loc (List.map (row_field sub) rl) b ll
    | Ptyp_poly (sl, t) -> poly ~loc sl (sub # typ t)
    | Ptyp_package (lid, l) -> package ~loc (map_loc sub lid) (List.map (map_tuple (map_loc sub) (sub # typ)) l)
    | Ptyp_attribute (body, x) -> attribute ~loc (sub # typ body) (sub # attribute x)
    | Ptyp_extension x -> extension ~loc (sub # extension x)

  let map_type_declaration sub td =
    {td with
     ptype_cstrs =
     List.map
       (fun (ct1, ct2, loc) -> sub # typ ct1, sub # typ ct2, sub # location loc)
       td.ptype_cstrs;
     ptype_kind = sub # type_kind td.ptype_kind;
     ptype_manifest = map_opt (sub # typ) td.ptype_manifest;
     ptype_loc = sub # location td.ptype_loc;
     ptype_attributes = map_attributes sub td.ptype_attributes;
    }

  let constructor_decl ?res ?(loc = Location.none) ?(attributes = []) name args =
    {
     pcd_name = name;
     pcd_args = args;
     pcd_res = res;
     pcd_loc = loc;
     pcd_attributes = attributes;
    }

  let map_constructor_decl sub {pcd_name; pcd_args; pcd_res; pcd_loc; pcd_attributes} =
    constructor_decl
      (map_loc sub pcd_name)
      (List.map (sub # typ) pcd_args)
      ?res:(map_opt (sub # typ) pcd_res)
      ~loc:(sub # location pcd_loc)
      ~attributes:(map_attributes sub pcd_attributes)

  let map_type_kind sub = function
    | Ptype_abstract -> Ptype_abstract
    | Ptype_variant l -> Ptype_variant (List.map (map_constructor_decl sub) l)
    | Ptype_record l -> Ptype_record (List.map (fun (s, flags, t, loc) -> (map_loc sub s, flags, sub # typ t, sub # location loc)) l)
end

module CT = struct
  (* Type expressions for the class language *)

  let mk ?(loc = Location.none) x = {pcty_loc = loc; pcty_desc = x}

  let constr ?loc a b = mk ?loc (Pcty_constr (a, b))
  let signature ?loc a = mk ?loc (Pcty_signature a)
  let fun_ ?loc a b c = mk ?loc (Pcty_fun (a, b, c))

  let map sub {pcty_loc = loc; pcty_desc = desc} =
    let loc = sub # location loc in
    match desc with
    | Pcty_constr (lid, tys) -> constr ~loc (map_loc sub lid) (List.map (sub # typ) tys)
    | Pcty_signature x -> signature ~loc (sub # class_signature x)
    | Pcty_fun (lab, t, ct) ->
        fun_ ~loc lab
          (sub # typ t)
          (sub # class_type ct)

  let mk_field ?(loc = Location.none) x = {pctf_desc = x; pctf_loc = loc}

  let inher ?loc a = mk_field ?loc (Pctf_inher a)
  let val_ ?loc a b c d = mk_field ?loc (Pctf_val (a, b, c, d))
  let virt ?loc a b c = mk_field ?loc (Pctf_virt (a, b, c))
  let meth ?loc a b c = mk_field ?loc (Pctf_meth (a, b, c))
  let cstr ?loc a b = mk_field ?loc (Pctf_cstr (a, b))

  let map_field sub {pctf_desc = desc; pctf_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Pctf_inher ct -> inher ~loc (sub # class_type ct)
    | Pctf_val (s, m, v, t) -> val_ ~loc s m v (sub # typ t)
    | Pctf_virt (s, p, t) -> virt ~loc s p (sub # typ t)
    | Pctf_meth (s, p, t) -> meth ~loc s p (sub # typ t)
    | Pctf_cstr (t1, t2) -> cstr ~loc (sub # typ t1) (sub # typ t2)

  let map_signature sub {pcsig_self; pcsig_fields; pcsig_loc} =
    {
     pcsig_self = sub # typ pcsig_self;
     pcsig_fields = List.map (sub # class_type_field) pcsig_fields;
     pcsig_loc = sub # location pcsig_loc ;
    }
end

module MT = struct
  (* Type expressions for the module language *)

  let mk ?(loc = Location.none) x = {pmty_desc = x; pmty_loc = loc}
  let ident ?loc a = mk ?loc (Pmty_ident a)
  let signature ?loc a = mk ?loc (Pmty_signature a)
  let functor_ ?loc a b c = mk ?loc (Pmty_functor (a, b, c))
  let with_ ?loc a b = mk ?loc (Pmty_with (a, b))
  let typeof_ ?loc a = mk ?loc (Pmty_typeof a)
  let attribute ?loc a b = mk ?loc (Pmty_attribute (a, b))
  let extension ?loc a = mk ?loc (Pmty_extension a)

  let map sub {pmty_desc = desc; pmty_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Pmty_ident s -> ident ~loc (map_loc sub s)
    | Pmty_signature sg -> signature ~loc (sub # signature sg)
    | Pmty_functor (s, mt1, mt2) -> functor_ ~loc (map_loc sub s) (sub # module_type mt1) (sub # module_type mt2)
    | Pmty_with (mt, l) -> with_ ~loc (sub # module_type mt) (List.map (map_tuple (map_loc sub) (sub # with_constraint)) l)
    | Pmty_typeof me -> typeof_ ~loc (sub # module_expr me)
    | Pmty_attribute (body, x) -> attribute ~loc (sub # module_type body) (sub # attribute x)
    | Pmty_extension x -> extension ~loc (sub # extension x)

  let map_with_constraint sub = function
    | Pwith_type d -> Pwith_type (sub # type_declaration d)
    | Pwith_module s -> Pwith_module (map_loc sub s)
    | Pwith_typesubst d -> Pwith_typesubst (sub # type_declaration d)
    | Pwith_modsubst s -> Pwith_modsubst (map_loc sub s)

  let mk_item ?(loc = Location.none) x = {psig_desc = x; psig_loc = loc}

  let value ?loc a b = mk_item ?loc (Psig_value (a, b))
  let type_ ?loc a = mk_item ?loc (Psig_type a)
  let exception_ ?loc a = mk_item ?loc (Psig_exception a)
  let module_ ?loc a = mk_item ?loc (Psig_module a)
  let rec_module ?loc a = mk_item ?loc (Psig_recmodule a)
  let modtype ?loc ?(attributes = []) a b = mk_item ?loc (Psig_modtype (a, b, attributes))
  let open_ ?loc ?(attributes = []) a = mk_item ?loc (Psig_open (a, attributes))
  let include_ ?loc ?(attributes = []) a = mk_item ?loc (Psig_include (a, attributes))
  let class_ ?loc a = mk_item ?loc (Psig_class a)
  let class_type ?loc a = mk_item ?loc (Psig_class_type a)
  let extension ?loc ?(attributes = []) a = mk_item ?loc (Psig_extension (a, attributes))

  let map_signature_item sub {psig_desc = desc; psig_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Psig_value (s, vd) -> value ~loc (map_loc sub s) (sub # value_description vd)
    | Psig_type l -> type_ ~loc (List.map (map_tuple (map_loc sub) (sub # type_declaration)) l)
    | Psig_exception ed -> exception_ ~loc (sub # exception_declaration ed)
    | Psig_module x -> module_ ~loc (sub # module_declaration x)
    | Psig_recmodule l -> rec_module ~loc (List.map (sub # module_declaration) l)
    | Psig_modtype (s, Pmodtype_manifest mt, attrs) -> modtype ~loc (map_loc sub s) (Pmodtype_manifest  (sub # module_type mt)) ~attributes:(map_attributes sub attrs)
    | Psig_modtype (s, Pmodtype_abstract, attrs) -> modtype ~loc (map_loc sub s) Pmodtype_abstract ~attributes:(map_attributes sub attrs)
    | Psig_open (lid, attrs) -> open_ ~loc ~attributes:(map_attributes sub attrs) (map_loc sub lid)
    | Psig_include (mt, attrs) -> include_ ~loc (sub # module_type mt) ~attributes:(map_attributes sub attrs)
    | Psig_class l -> class_ ~loc (List.map (sub # class_description) l)
    | Psig_class_type l -> class_type ~loc (List.map (sub # class_type_declaration) l)
    | Psig_extension (x, attrs) -> extension ~loc (sub # extension x) ~attributes:(map_attributes sub attrs)
end


module M = struct
  (* Value expressions for the module language *)

  let mk ?(loc = Location.none) x = {pmod_desc = x; pmod_loc = loc}
  let ident ?loc x = mk ?loc (Pmod_ident x)
  let structure ?loc x = mk ?loc (Pmod_structure x)
  let functor_ ?loc arg arg_ty body = mk ?loc (Pmod_functor (arg, arg_ty, body))
  let apply ?loc m1 m2 = mk ?loc (Pmod_apply (m1, m2))
  let constraint_ ?loc m mty = mk ?loc (Pmod_constraint (m, mty))
  let unpack ?loc e = mk ?loc (Pmod_unpack e)
  let attribute ?loc a b = mk ?loc (Pmod_attribute (a, b))
  let extension ?loc a = mk ?loc (Pmod_extension a)

  let map sub {pmod_loc = loc; pmod_desc = desc} =
    let loc = sub # location loc in
    match desc with
    | Pmod_ident x -> ident ~loc (map_loc sub x)
    | Pmod_structure str -> structure ~loc (sub # structure str)
    | Pmod_functor (arg, arg_ty, body) -> functor_ ~loc (map_loc sub arg) (sub # module_type arg_ty) (sub # module_expr body)
    | Pmod_apply (m1, m2) -> apply ~loc (sub # module_expr m1) (sub # module_expr m2)
    | Pmod_constraint (m, mty) -> constraint_ ~loc (sub # module_expr m) (sub # module_type mty)
    | Pmod_unpack e -> unpack ~loc (sub # expr e)
    | Pmod_attribute (body, x) -> attribute ~loc (sub # module_expr body) (sub # attribute x)
    | Pmod_extension x -> extension ~loc (sub # extension x)

  let mk_item ?(loc = Location.none) x = {pstr_desc = x; pstr_loc = loc}
  let eval ?loc a = mk_item ?loc (Pstr_eval a)
  let value ?loc a b = mk_item ?loc (Pstr_value (a, b))
  let primitive ?loc a b = mk_item ?loc (Pstr_primitive (a, b))
  let type_ ?loc a = mk_item ?loc (Pstr_type a)
  let exception_ ?loc a = mk_item ?loc (Pstr_exception a)
  let exn_rebind ?loc ?(attributes = []) a b = mk_item ?loc (Pstr_exn_rebind (a, b, attributes))
  let module_ ?loc a = mk_item ?loc (Pstr_module a)
  let rec_module ?loc a = mk_item ?loc (Pstr_recmodule a)
  let modtype ?loc a b = mk_item ?loc (Pstr_modtype (a, b))
  let open_ ?loc ?(attributes = []) a = mk_item ?loc (Pstr_open (a, attributes))
  let class_ ?loc a = mk_item ?loc (Pstr_class a)
  let class_type ?loc a = mk_item ?loc (Pstr_class_type a)
  let include_ ?loc ?(attributes = []) a = mk_item ?loc (Pstr_include (a, attributes))
  let extension ?loc ?(attributes = []) a = mk_item ?loc (Pstr_extension (a, attributes))

  let map_structure_item sub {pstr_loc = loc; pstr_desc = desc} =
    let loc = sub # location loc in
    match desc with
    | Pstr_eval x -> eval ~loc (sub # expr x)
    | Pstr_value (r, pel) -> value ~loc r (List.map (map_tuple (sub # pat) (sub # expr)) pel)
    | Pstr_primitive (name, vd) -> primitive ~loc (map_loc sub name) (sub # value_description vd)
    | Pstr_type l -> type_ ~loc (List.map (map_tuple (map_loc sub) (sub # type_declaration)) l)
    | Pstr_exception ed -> exception_ ~loc (sub # exception_declaration ed)
    | Pstr_exn_rebind (s, lid, attrs) -> exn_rebind ~loc (map_loc sub s) (map_loc sub lid) ~attributes:(map_attributes sub attrs)
    | Pstr_module x -> module_ ~loc (sub # module_binding x)
    | Pstr_recmodule l -> rec_module ~loc (List.map (sub # module_binding) l)
    | Pstr_modtype (s, mty) -> modtype ~loc (map_loc sub s) (sub # module_type mty)
    | Pstr_open (lid, attrs) -> open_ ~loc ~attributes:(map_attributes sub attrs) (map_loc sub lid)
    | Pstr_class l -> class_ ~loc (List.map (sub # class_declaration) l)
    | Pstr_class_type l -> class_type ~loc (List.map (sub # class_type_declaration) l)
    | Pstr_include (e, attrs) -> include_ ~loc (sub # module_expr e) ~attributes:(map_attributes sub attrs)
    | Pstr_extension (x, attrs) -> extension ~loc (sub # extension x) ~attributes:(map_attributes sub attrs)
end

module E = struct
  (* Value expressions for the core language *)

  let mk ?(loc = Location.none) x = {pexp_desc = x; pexp_loc = loc}

  let ident ?loc a = mk ?loc (Pexp_ident a)
  let constant ?loc a = mk ?loc (Pexp_constant a)
  let let_ ?loc a b c = mk ?loc (Pexp_let (a, b, c))
  let function_ ?loc a b c = mk ?loc (Pexp_function (a, b, c))
  let apply ?loc a b = mk ?loc (Pexp_apply (a, b))
  let match_ ?loc a b = mk ?loc (Pexp_match (a, b))
  let try_ ?loc a b = mk ?loc (Pexp_try (a, b))
  let tuple ?loc a = mk ?loc (Pexp_tuple a)
  let construct ?loc a b c = mk ?loc (Pexp_construct (a, b, c))
  let variant ?loc a b = mk ?loc (Pexp_variant (a, b))
  let record ?loc a b = mk ?loc (Pexp_record (a, b))
  let field ?loc a b = mk ?loc (Pexp_field (a, b))
  let setfield ?loc a b c = mk ?loc (Pexp_setfield (a, b, c))
  let array ?loc a = mk ?loc (Pexp_array a)
  let ifthenelse ?loc a b c = mk ?loc (Pexp_ifthenelse (a, b, c))
  let sequence ?loc a b = mk ?loc (Pexp_sequence (a, b))
  let while_ ?loc a b = mk ?loc (Pexp_while (a, b))
  let for_ ?loc a b c d e = mk ?loc (Pexp_for (a, b, c, d, e))
  let constraint_ ?loc a b c = mk ?loc (Pexp_constraint (a, b, c))
  let when_ ?loc a b = mk ?loc (Pexp_when (a, b))
  let send ?loc a b = mk ?loc (Pexp_send (a, b))
  let new_ ?loc a = mk ?loc (Pexp_new a)
  let setinstvar ?loc a b = mk ?loc (Pexp_setinstvar (a, b))
  let override ?loc a = mk ?loc (Pexp_override a)
  let letmodule ?loc (a, b, c)= mk ?loc (Pexp_letmodule (a, b, c))
  let assert_ ?loc a = mk ?loc (Pexp_assert a)
  let assertfalse ?loc () = mk ?loc Pexp_assertfalse
  let lazy_ ?loc a = mk ?loc (Pexp_lazy a)
  let poly ?loc a b = mk ?loc (Pexp_poly (a, b))
  let object_ ?loc a = mk ?loc (Pexp_object a)
  let newtype ?loc a b = mk ?loc (Pexp_newtype (a, b))
  let pack ?loc a = mk ?loc (Pexp_pack a)
  let open_ ?loc a b = mk ?loc (Pexp_open (a, b))
  let attribute ?loc a b = mk ?loc (Pexp_attribute (a, b))
  let extension ?loc a = mk ?loc (Pexp_extension a)

  let lid ?(loc = Location.none) lid = ident ~loc (mkloc (Longident.parse lid) loc)
  let apply_nolabs ?loc f el = apply ?loc f (List.map (fun e -> ("", e)) el)
  let strconst ?loc x = constant ?loc (Const_string x)

  let map sub {pexp_loc = loc; pexp_desc = desc} =
    let loc = sub # location loc in
    match desc with
    | Pexp_ident x -> ident ~loc (map_loc sub x)
    | Pexp_constant x -> constant ~loc x
    | Pexp_let (r, pel, e) -> let_ ~loc r (List.map (map_tuple (sub # pat) (sub # expr)) pel) (sub # expr e)
    | Pexp_function (lab, def, pel) -> function_ ~loc lab (map_opt (sub # expr) def) (List.map (map_tuple (sub # pat) (sub # expr)) pel)
    | Pexp_apply (e, l) -> apply ~loc (sub # expr e) (List.map (map_snd (sub # expr)) l)
    | Pexp_match (e, l) -> match_ ~loc (sub # expr e) (List.map (map_tuple (sub # pat) (sub # expr)) l)
    | Pexp_try (e, l) -> try_ ~loc (sub # expr e) (List.map (map_tuple (sub # pat) (sub # expr)) l)
    | Pexp_tuple el -> tuple ~loc (List.map (sub # expr) el)
    | Pexp_construct (lid, arg, b) -> construct ~loc (map_loc sub lid) (map_opt (sub # expr) arg) b
    | Pexp_variant (lab, eo) -> variant ~loc lab (map_opt (sub # expr) eo)
    | Pexp_record (l, eo) -> record ~loc (List.map (map_tuple (map_loc sub) (sub # expr)) l) (map_opt (sub # expr) eo)
    | Pexp_field (e, lid) -> field ~loc (sub # expr e) (map_loc sub lid)
    | Pexp_setfield (e1, lid, e2) -> setfield ~loc (sub # expr e1) (map_loc sub lid) (sub # expr e2)
    | Pexp_array el -> array ~loc (List.map (sub # expr) el)
    | Pexp_ifthenelse (e1, e2, e3) -> ifthenelse ~loc (sub # expr e1) (sub # expr e2) (map_opt (sub # expr) e3)
    | Pexp_sequence (e1, e2) -> sequence ~loc (sub # expr e1) (sub # expr e2)
    | Pexp_while (e1, e2) -> while_ ~loc (sub # expr e1) (sub # expr e2)
    | Pexp_for (id, e1, e2, d, e3) -> for_ ~loc (map_loc sub id) (sub # expr e1) (sub # expr e2) d (sub # expr e3)
    | Pexp_constraint (e, t1, t2) -> constraint_ ~loc (sub # expr e) (map_opt (sub # typ) t1) (map_opt (sub # typ) t2)
    | Pexp_when (e1, e2) -> when_ ~loc (sub # expr e1) (sub # expr e2)
    | Pexp_send (e, s) -> send ~loc (sub # expr e) s
    | Pexp_new lid -> new_ ~loc (map_loc sub lid)
    | Pexp_setinstvar (s, e) -> setinstvar ~loc (map_loc sub s) (sub # expr e)
    | Pexp_override sel -> override ~loc (List.map (map_tuple (map_loc sub) (sub # expr)) sel)
    | Pexp_letmodule (s, me, e) -> letmodule ~loc (map_loc sub s, sub # module_expr me, sub # expr e)
    | Pexp_assert e -> assert_ ~loc (sub # expr e)
    | Pexp_assertfalse -> assertfalse ~loc ()
    | Pexp_lazy e -> lazy_ ~loc (sub # expr e)
    | Pexp_poly (e, t) -> poly ~loc (sub # expr e) (map_opt (sub # typ) t)
    | Pexp_object cls -> object_ ~loc (sub # class_structure cls)
    | Pexp_newtype (s, e) -> newtype ~loc s (sub # expr e)
    | Pexp_pack me -> pack ~loc (sub # module_expr me)
    | Pexp_open (lid, e) -> open_ ~loc (map_loc sub lid) (sub # expr e)
    | Pexp_attribute (body, x) -> attribute ~loc (sub # expr body) (sub # attribute x)
    | Pexp_extension x -> extension ~loc (sub # extension x)
end

module P = struct
  (* Patterns *)

  let mk ?(loc = Location.none) x = {ppat_desc = x; ppat_loc = loc}
  let any ?loc () = mk ?loc Ppat_any
  let var ?loc a = mk ?loc (Ppat_var a)
  let alias ?loc a b = mk ?loc (Ppat_alias (a, b))
  let constant ?loc a = mk ?loc (Ppat_constant a)
  let tuple ?loc a = mk ?loc (Ppat_tuple a)
  let construct ?loc a b c = mk ?loc (Ppat_construct (a, b, c))
  let variant ?loc a b = mk ?loc (Ppat_variant (a, b))
  let record ?loc a b = mk ?loc (Ppat_record (a, b))
  let array ?loc a = mk ?loc (Ppat_array a)
  let or_ ?loc a b = mk ?loc (Ppat_or (a, b))
  let constraint_ ?loc a b = mk ?loc (Ppat_constraint (a, b))
  let type_ ?loc a = mk ?loc (Ppat_type a)
  let lazy_ ?loc a = mk ?loc (Ppat_lazy a)
  let unpack ?loc a = mk ?loc (Ppat_unpack a)
  let attribute ?loc a b = mk ?loc (Ppat_attribute (a, b))
  let extension ?loc a = mk ?loc (Ppat_extension a)

  let map sub {ppat_desc = desc; ppat_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Ppat_any -> any ~loc ()
    | Ppat_var s -> var ~loc (map_loc sub s)
    | Ppat_alias (p, s) -> alias ~loc (sub # pat p) (map_loc sub s)
    | Ppat_constant c -> constant ~loc c
    | Ppat_tuple pl -> tuple ~loc (List.map (sub # pat) pl)
    | Ppat_construct (l, p, b) -> construct ~loc (map_loc sub l) (map_opt (sub # pat) p) b
    | Ppat_variant (l, p) -> variant ~loc l (map_opt (sub # pat) p)
    | Ppat_record (lpl, cf) ->
        record ~loc (List.map (map_tuple (map_loc sub) (sub # pat)) lpl) cf
    | Ppat_array pl -> array ~loc (List.map (sub # pat) pl)
    | Ppat_or (p1, p2) -> or_ ~loc (sub # pat p1) (sub # pat p2)
    | Ppat_constraint (p, t) -> constraint_ ~loc (sub # pat p) (sub # typ t)
    | Ppat_type s -> type_ ~loc (map_loc sub s)
    | Ppat_lazy p -> lazy_ ~loc (sub # pat p)
    | Ppat_unpack s -> unpack ~loc (map_loc sub s)
    | Ppat_attribute (body, x) -> attribute ~loc (sub # pat body) (sub # attribute x)
    | Ppat_extension x -> extension ~loc (sub # extension x)
end

module CE = struct
  (* Value expressions for the class language *)

  let mk ?(loc = Location.none) x = {pcl_loc = loc; pcl_desc = x}

  let constr ?loc a b = mk ?loc (Pcl_constr (a, b))
  let structure ?loc a = mk ?loc (Pcl_structure a)
  let fun_ ?loc a b c d = mk ?loc (Pcl_fun (a, b, c, d))
  let apply ?loc a b = mk ?loc (Pcl_apply (a, b))
  let let_ ?loc a b c = mk ?loc (Pcl_let (a, b, c))
  let constraint_ ?loc a b = mk ?loc (Pcl_constraint (a, b))

  let map sub {pcl_loc = loc; pcl_desc = desc} =
    let loc = sub # location loc in
    match desc with
    | Pcl_constr (lid, tys) -> constr ~loc (map_loc sub lid) (List.map (sub # typ) tys)
    | Pcl_structure s ->
        structure ~loc (sub # class_structure s)
    | Pcl_fun (lab, e, p, ce) ->
        fun_ ~loc lab
          (map_opt (sub # expr) e)
          (sub # pat p)
          (sub # class_expr ce)
    | Pcl_apply (ce, l) ->
        apply ~loc (sub # class_expr ce) (List.map (map_snd (sub # expr)) l)
    | Pcl_let (r, pel, ce) ->
        let_ ~loc r
          (List.map (map_tuple (sub # pat) (sub # expr)) pel)
          (sub # class_expr ce)
    | Pcl_constraint (ce, ct) ->
        constraint_ ~loc (sub # class_expr ce) (sub # class_type ct)


  let mk_field ?(loc = Location.none) x = {pcf_desc = x; pcf_loc = loc}

  let inher ?loc a b c = mk_field ?loc (Pcf_inher (a, b, c))
  let valvirt ?loc a b c = mk_field ?loc (Pcf_valvirt (a, b, c))
  let val_ ?loc a b c d = mk_field ?loc (Pcf_val (a, b, c, d))
  let virt ?loc a b c = mk_field ?loc (Pcf_virt (a, b, c))
  let meth ?loc a b c d = mk_field ?loc (Pcf_meth (a, b, c, d))
  let constr ?loc a b = mk_field ?loc (Pcf_constr (a, b))
  let init ?loc a = mk_field ?loc (Pcf_init a)

  let map_field sub {pcf_desc = desc; pcf_loc = loc} =
    let loc = sub # location loc in
    match desc with
    | Pcf_inher (o, ce, s) -> inher ~loc o (sub # class_expr ce) s
    | Pcf_valvirt (s, m, t) -> valvirt ~loc (map_loc sub s) m (sub # typ t)
    | Pcf_val (s, m, o, e) -> val_ ~loc (map_loc sub s) m o (sub # expr e)
    | Pcf_virt (s, p, t) -> virt ~loc (map_loc sub s) p (sub # typ t)
    | Pcf_meth (s, p, o, e) -> meth ~loc (map_loc sub s) p o (sub # expr e)
    | Pcf_constr (t1, t2) -> constr ~loc (sub # typ t1) (sub # typ t2)
    | Pcf_init e -> init ~loc (sub # expr e)

  let map_structure sub {pcstr_pat; pcstr_fields} =
    {
     pcstr_pat = sub # pat pcstr_pat;
     pcstr_fields = List.map (sub # class_field) pcstr_fields;
    }

  let class_infos sub f {pci_virt; pci_params = (pl, ploc); pci_name; pci_expr; pci_variance; pci_loc; pci_attributes} =
    {
     pci_virt;
     pci_params = List.map (map_loc sub) pl, sub # location ploc;
     pci_name = map_loc sub pci_name;
     pci_expr = f pci_expr;
     pci_variance;
     pci_loc = sub # location pci_loc;
     pci_attributes = map_attributes sub pci_attributes;
    }
end

(* Now, a generic AST mapper class, to be extended to cover all kinds
   and cases of the OCaml grammar.  The default behavior of the mapper
   is the identity. *)

class mapper =
  object(this)
    method implementation (input_name : string) ast = (input_name, this # structure ast)
    method interface (input_name: string) ast = (input_name, this # signature ast)
    method structure l = List.map (this # structure_item) l
    method structure_item si = M.map_structure_item this si
    method module_expr = M.map this

    method signature l = List.map (this # signature_item) l
    method signature_item si = MT.map_signature_item this si
    method module_type = MT.map this
    method with_constraint c = MT.map_with_constraint this c

    method class_declaration = CE.class_infos this (this # class_expr)
    method class_expr = CE.map this
    method class_field = CE.map_field this
    method class_structure = CE.map_structure this

    method class_type = CT.map this
    method class_type_field = CT.map_field this
    method class_signature = CT.map_signature this

    method class_type_declaration = CE.class_infos this (this # class_type)
    method class_description = CE.class_infos this (this # class_type)

    method type_declaration = T.map_type_declaration this
    method type_kind = T.map_type_kind this
    method typ = T.map this

    method value_description {pval_type; pval_prim; pval_loc; pval_attributes} =
      {
       pval_type = this # typ pval_type;
       pval_prim;
       pval_loc = this # location pval_loc;
       pval_attributes = map_attributes this pval_attributes;
      }
    method pat = P.map this
    method expr = E.map this

    method exception_declaration ped =
      {
       ped_name = map_loc this ped.ped_name;
       ped_args = List.map (this # typ) ped.ped_args;
       ped_attributes = map_attributes this ped.ped_attributes;
      }
    method module_declaration pmd =
      {
       pmd_name = map_loc this pmd.pmd_name;
       pmd_type = this # module_type pmd.pmd_type;
       pmd_attributes = map_attributes this pmd.pmd_attributes;
      }
    method module_binding x =
      {
       pmb_name = map_loc this x.pmb_name;
       pmb_expr = this # module_expr x.pmb_expr;
       pmb_attributes = map_attributes this x.pmb_attributes;
      }

    method location l = l

    method extension (s, e) = (s, this # expr e)
    method attribute (s, e) = (s, this # expr e)
  end

class type main_entry_points =
  object
    method implementation: string -> structure -> string * structure
    method interface: string -> signature -> string * signature
  end

let apply ~source ~target mapper =
  let ic = open_in_bin source in
  let magic = String.create (String.length ast_impl_magic_number) in
  really_input ic magic 0 (String.length magic);
  if magic <> ast_impl_magic_number && magic <> ast_intf_magic_number then
    failwith "Bad magic";
  let input_name = input_value ic in
  let ast = input_value ic in
  close_in ic;

  let (input_name, ast) =
    if magic = ast_impl_magic_number
    then Obj.magic (mapper # implementation input_name (Obj.magic ast))
    else Obj.magic (mapper # interface input_name (Obj.magic ast))
  in
  let oc = open_out_bin target in
  output_string oc magic;
  output_value oc input_name;
  output_value oc ast;
  close_out oc

let run_main mapper =
  try
    let a = Sys.argv in
    let n = Array.length a in
    if n > 2 then
      apply ~source:a.(n - 2) ~target:a.(n - 1) (mapper (Array.to_list (Array.sub a 1 (n - 3))))
    else begin
      Printf.eprintf "Usage: %s [extra_args] <infile> <outfile>\n%!" Sys.executable_name;
      exit 1
    end
  with exn ->
    prerr_endline (Printexc.to_string exn);
    exit 2

let main mapper = run_main (fun _ -> mapper)

let register_function = ref (fun _name f -> run_main f)
let register name f = !register_function name (f :> string list -> mapper)