[erlang-questions] Function Reference to Code Tree

[Ulf Wiger]

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



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