Inspecting anonymous functions
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Tallak Tveide
Jul 13, 2014, 6:50:57 PM7/13/14
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Using anonymous functions for me is nice, but I do find it har to debug when I cannot see what they contain. That's why I'm thinking it would be nice to have an inspect function for anonymous functions that could print out the function and any bound data, eg:
iex(2)> f = fn x -> fn -> x + 10 end end
#Function<6.106461118/1 in :erl_eval.expr/5>
iex(3)> Function.inspect f
# function at file ffff line llll
fn x ->
fn ->
x + 10
end
end
iex(4)> Function.inspect f.(10)
# function at file ffff line llll
fn ->
10 + 10
end
Would this be possible to implement somehow? Right now there doesn't seem to be an interface into a function value... Macros won't work as this would happen at runtime I guess..
iex(2)> f = fn x -> fn -> x + 10 end end
#Function<6.106461118/1 in :erl_eval.expr/5>
iex(3)> Function.inspect f
# function at file ffff line llll
fn x ->
fn ->
x + 10
end
end
iex(4)> Function.inspect f.(10)
# function at file ffff line llll
fn ->
10 + 10
end
Would this be possible to implement somehow? Right now there doesn't seem to be an interface into a function value... Macros won't work as this would happen at runtime I guess..
José Valim
Jul 14, 2014, 5:44:31 AM7/14/14
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Unfortunately we can't do that right now.
I know Erlang stores its abstract format in functions [1] and maybe we can do the same once we change our compiler to compile to core erlang (instead of erlang abstract format) but this change is not happening in the short term because it breaks things like dialyzer.
[1] Try in your iex shell: :erlang.fun_info(fn x, y -> x + y end)
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Robert Virding
Jul 14, 2014, 7:30:29 AM7/14/14
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This only works when the fun is defined in the shell, i.e. when it is interpreted. Funs from modules don't contain the abstract code, at least not so :erlang.fun_info gets it.
The reason it works with interpreted code is a result of how funs are implemented in erl_eval, the erlang interpreter. It uses internal funs in erl_eval and the abstract code is passed as data into those funs which is then interpreted when the fun is called. A nice hack.
Robert
The reason it works with interpreted code is a result of how funs are implemented in erl_eval, the erlang interpreter. It uses internal funs in erl_eval and the abstract code is passed as data into those funs which is then interpreted when the fun is called. A nice hack.
Robert
José Valim
Jul 14, 2014, 7:48:36 AM7/14/14
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Ah, nice to know, thanks Robert!
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