just playing with ppx

Makefile

build:
	ocamlbuild -use-ocamlfind -package compiler-libs.common,ppx_tools.metaquot \
	ppx_component.native

infer:
	ocamlbuild -use-ocamlfind -package compiler-libs.common,ppx_tools.metaquot \
	ppx_component.inferred.mli

test: build
	ocamlopt -I lib -ppx ./ppx_component.native ./test_ppx_component.ml -o ./test_ppx_component.native

ppx_component.ml

open Ast_mapper
open Ast_helper
open Asttypes
open Parsetree
open Longident
open Location

let get_vb stru_item = 
  match stru_item with
  |{pstr_desc =
   Pstr_value (Nonrecursive,
    [{pvb_pat  = {ppat_desc = Ppat_var {txt = id}};
      pvb_expr = {pexp_desc = Pexp_fun (_, _,
        {ppat_desc = Ppat_extension ({txt = "getvb"}, PStr [])},_)}}])} ->
      Some id 
  | _ -> None


let stru_mapper = fun mapper stru_items ->
  match stru_items with
  | [] -> default_mapper.structure mapper stru_items
  | stru_item :: _ ->
     match get_vb stru_item with
     | Some id -> let pr_stru = [%str let p () = print_endline id] in
        (default_mapper.structure mapper stru_items) @ pr_stru
     | None -> default_mapper.structure mapper stru_items

let getvb_mapper argv =
  {default_mapper with structure = stru_mapper}

let () = Ast_mapper.register "getvb" getvb_mapper

test_ppx_component.ml

let f[%getvb] x = x + 1