unikernel/duniverse/ppxlib/examples/simple-deriver/ppx_deriving_accessors.ml

@@ -0,0 +1,78 @@
+open Ppxlib
+module List = ListLabels
+open Ast_builder.Default
+
+let accessor_impl (ld : label_declaration) =
+  let loc = ld.pld_loc in
+  pstr_value ~loc Nonrecursive
+    [
+      {
+        pvb_pat = ppat_var ~loc ld.pld_name;
+        pvb_expr =
+          pexp_fun ~loc Nolabel None
+            (ppat_var ~loc { loc; txt = "x" })
+            (pexp_field ~loc
+               (pexp_ident ~loc { loc; txt = lident "x" })
+               { loc; txt = lident ld.pld_name.txt });
+        pvb_attributes = [];
+        pvb_loc = loc;
+        pvb_constraint = None;
+      };
+    ]
+
+let accessor_intf ~ptype_name (ld : label_declaration) =
+  let loc = ld.pld_loc in
+  psig_value ~loc
+    {
+      pval_name = ld.pld_name;
+      pval_type =
+        ptyp_arrow ~loc Nolabel
+          (ptyp_constr ~loc { loc; txt = lident ptype_name.txt } [])
+          ld.pld_type;
+      pval_attributes = [];
+      pval_loc = loc;
+      pval_prim = [];
+    }
+
+let generate_impl ~ctxt (_rec_flag, type_declarations) =
+  let loc = Expansion_context.Deriver.derived_item_loc ctxt in
+  List.map type_declarations ~f:(fun (td : type_declaration) ->
+      match td with
+      | {
+       ptype_kind = Ptype_abstract | Ptype_variant _ | Ptype_open;
+       ptype_loc;
+       _;
+      } ->
+          let ext =
+            Location.error_extensionf ~loc:ptype_loc
+              "Cannot derive accessors for non record types"
+          in
+          [ Ast_builder.Default.pstr_extension ~loc ext [] ]
+      | { ptype_kind = Ptype_record fields; _ } ->
+          List.map fields ~f:accessor_impl)
+  |> List.concat
+
+let generate_intf ~ctxt (_rec_flag, type_declarations) =
+  let loc = Expansion_context.Deriver.derived_item_loc ctxt in
+  List.map type_declarations ~f:(fun (td : type_declaration) ->
+      match td with
+      | {
+       ptype_kind = Ptype_abstract | Ptype_variant _ | Ptype_open;
+       ptype_loc;
+       _;
+      } ->
+          let ext =
+            Location.error_extensionf ~loc:ptype_loc
+              "Cannot derive accessors for non record types"
+          in
+          [ Ast_builder.Default.psig_extension ~loc ext [] ]
+      | { ptype_kind = Ptype_record fields; ptype_name; _ } ->
+          List.map fields ~f:(accessor_intf ~ptype_name))
+  |> List.concat
+
+let impl_generator = Deriving.Generator.V2.make_noarg generate_impl
+let intf_generator = Deriving.Generator.V2.make_noarg generate_intf
+
+let my_deriver =
+  Deriving.add "accessors" ~str_type_decl:impl_generator
+    ~sig_type_decl:intf_generator