Knowing the number of parameters of a passed function (erlang)

问题

In ERLANG: Assume we have a function f() that takes F1 as inputs where F1 is a function. Is there a way to know the number of input parameters of F1.

I feel somehow there IS a solution, but I am not sure. for instance:

 -module(high).
 -compile(export_all).

 f1() -> 1.
 f2(X) -> X. 
 f3(X, Y) -> {X,Y}. 

 run(F) -> io:format("F ~p ~n", [F]).

So, is there any way for function run/1 to know information about the passed function [mainly the number of input parameters of the passed function].

Note: Please be informed that this is a theoretical question. Note: is the code of apply(fun,[arguments]) available in open-source .. this may hep me I guess.

回答1:

erlang:fun_info(Fun,arity).

For example

F = fun(A,B) -> A+B end.
#Fun<erl_eval.12.111823515>
3> erlang:fun_info(F,arity).
{arity,2}

回答2:

You can use module_info/1 to get info about your module.

module_info/1

The call module_info(Key), where Key is an atom, returns a single piece of information about the module.

The following values are allowed for Key:

...

exports Returns a list of {Name,Arity} tuples with all exported functions in the module.

functions Returns a list of {Name,Arity} tuples with all functions in the module.

http://erlang.org/doc/reference_manual/modules.html

run(F) -> find_value(F,module_info(exports)).

find_value(Key, List) ->
    case lists:keyfind(Key, 1, List) of
        {Key, Result} -> {Key,Result};
        false -> io:format("There is no function called ~w.~n", [Key])
    end.

来源：https://stackoverflow.com/questions/10048001/knowing-the-number-of-parameters-of-a-passed-function-erlang

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erlang