[erlang-questions] [proposal] Declarative syntax for metadata (long!)

Ulf Wiger <>
Sat Apr 10 13:58:11 CEST 2010


Michael Truog wrote:
> Hi,
> 
> I was hoping to bring up this thread because it does relate to a task I
> am trying to do in Erlang.  To avoid re-parsing a compiled module to
> generate this information I was hoping to use the loaded binary beam
> data.  My use case is for automatically generating RPC function
> definitions from an API module, which I think would be neat.
> 
> One small thing that would make this easier, is if
> "-compile(debug_info)." worked.  The documentation says it does:
> "Note that all the options except the include path ({i,Dir}) can also be
> given in the file" (http://erlang.org/doc/man/compile.html#debug_info)

The following code might serve as a quick-and-dirty workaround,
and also provide much faster access to the abstract code:

-module(include_forms).
-export([parse_transform/2]).

parse_transform(Forms, _) ->
     [EoF|Rev] = lists:reverse(Forms),
     Forms1 = lists:reverse([EoF,absfun(Forms)|Rev]),
     {Attrs,Funs} = lists:splitwith(fun(F) ->
                                            element(1,F) == attribute
                                    end, Forms1),
     Attrs ++ [{attribute,1,export,[{'$abstract_code$',0}]} | Funs].

absfun(Forms) ->
     {function, 1, '$abstract_code$', 0,
      [{clause,1,[],[],
        [erl_parse:abstract(Forms)]}]}.



Eshell V5.7.5  (abort with ^G)
1> c(include_forms).
{ok,include_forms}
2> c(include_forms, [{parse_transform,include_forms}]).
{ok,include_forms}
3> include_forms:'$abstract_code$'().
[{attribute,1,file,{"./include_forms.erl",1}},
  {attribute,1,module,include_forms},
  {attribute,2,export,[{parse_transform,2}]},
  {function,4,parse_transform,2,
            [{clause,4,
                     [{var,4,'Forms'},{var,4,'_'}],
                     [],
                     [{match,5,
                             {cons,5,{var,5,'EoF'},{var,5,'Rev'}},
                             {call,5,
                                   {remote,5,{atom,5,lists},{atom,5,...}},
                                   [{var,5,'Forms'}]}},


The parse_transform directive can certainly be included in
a module, as well as buried in a .hrl file.

BR,
Ulf W
-- 
Ulf Wiger
CTO, Erlang Solutions Ltd, formerly Erlang Training & Consulting Ltd
http://www.erlang-solutions.com
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