[erlang-questions] Function Reference to Code Tree

Tyron Zerafa <>
Wed Jan 23 11:35:58 CET 2013


Fantastic, this is exactly what I had in mind :) I will surely give it a
try (and some thought about the effect of free vars)
Thanks


On Wed, Jan 23, 2013 at 11:07 AM, Ulf Wiger <> wrote:

>
> On 22 Jan 2013, at 20:11, Tyron Zerafa wrote:
>
> Erlang:fun_info(F) is returning the function body because it is
> constructed in the shell which essentially passes the entire code tree to
> the erl_eval module for execution. If you call this for a function
> constructed in a module, you won't get this tree.
>
> I need something along these lines that work for functions constructed in
> modules rather than the shell.
>
>
> Mind you, this is just example code - not intended for mission-critical
> use.
>
> http://erlang.org/pipermail/erlang-questions/2007-December/031992.html
>
> I updated the program a little bit, since the internal naming of funs
> seems to have changed:
>
>
> -module(extract).
>
> -export([f/1]).
>
>
> f(F) ->
>    {module, Mod} = erlang:fun_info(F, module),
>    {name, Name} = erlang:fun_info(F, name),
>    {ok, Abst} = get_abstract_code(Mod),
>    extract_fun(Name, Abst).
>
> get_abstract_code(Module) ->
>    {module,_} = code:ensure_loaded(Module),
>    Beam = code:which(Module),
>    case beam_lib:chunks(Beam, [abstract_code]) of
> {ok,{_,[{abstract_code,{_,AC}}]}} ->
>     {ok, AC};
> Other ->
>     Other
>    end.
>
> extract_fun(Name, AC) ->
>    {F,Arity,Rel} = split_name(Name),
>    Clauses = [Cs || {function,_,F1,Arity1,Cs} <- AC,
>      F1 == F, Arity1 == Arity],
>    Funs = pick_funs(lists:concat(Clauses)),
>    lists:nth(Rel, Funs).
>
> split_name(Name) ->
>     [Fs, As, _, Rs] = string:tokens(atom_to_list(Name),"/-"),
>    {list_to_atom(Fs), list_to_integer(As), list_to_integer(Rs)+1}.
>
> pick_funs(L) ->
>    Flatten = fun({'fun',_,_} = Fun) -> [Fun];
>  (T) when is_tuple(T) -> tuple_to_list(T);
>  (_) -> []
>       end,
>    L1 = [X || X <- lists:flatten(lists:map(Flatten, L)),
>        is_tuple(X)],
>    case [F || F <- L1,
>        element(1, F) =/= 'fun'] of
> [] -> L1;
> [_|_] ->
>     pick_funs(L1)
>    end.
>
>
> Example:
>
> -module(m1).
>
> -export([f/2]).
>
> f(N, X) ->
>    if  N==1; N==2 ->
>     element(N, {fun() ->
>         X + 1
>         end,
>         fun() ->
>         X - 1
>         end});
> N == 3 ->
>     fun(Y) ->
>     X + Y
>     end
>    end.
>
> Eshell V5.9.2  (abort with ^G)
> 1> [m1:f(N,17) || N <- [1,2,3]].
> [#Fun<m1.0.1800644>,#Fun<m1.1.1800644>,#Fun<m1.2.1800644>]
> 2> [extract:f(m1:f(N,17)) || N <- [1,2,3]].
> [{'fun',7,
>         {clauses,[{clause,7,[],[],
>                           [{op,8,'+',{var,8,'X'},{integer,8,1}}]}]}},
>  {'fun',10,
>         {clauses,[{clause,10,[],[],
>                           [{op,11,'-',{var,11,'X'},{integer,11,1}}]}]}},
>  {'fun',14,
>         {clauses,[{clause,14,
>                           [{var,14,'Y'}],
>                           [],
>                           [{op,15,'+',{var,15,'X'},{var,15,'Y'}}]}]}}]
>
>
> The module m1 needs to be compiled with debug_info, of course.
>
> BR,
> Ulf W
>
> Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.
> http://feuerlabs.com
>
>
>
>


-- 
Best Regards,
Tyron Zerafa
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