Adding support for `binary_part`

[jdcumpson]

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Hello! Thanks for contributing this repo.

I'm currently trying to add support for binary_part as it is allowed as a guard in both erlang and elixir.

Adding :binary_part to @extra_guard_functions I expected the following test to work

test "binary_part" do
    prefix = "1234"

    ms =
      fun do
        bid when binary_part(bid, 0, 4) == ^prefix -> bid
      end

    assert ms == [{:"$1", [{:==, {:binary_part, :"$1", 0, 4}, {:const, prefix}}], [:"$1"]}]
    assert {:ok, "12345"} == :ets.test_ms("12345", ms)
  end

But I am getting the following output:

1) test binary_part (Ex2msTest)
     test/ex2ms_test.exs:319
     Assertion with == failed
     code:  assert {:ok, "12345"} == :ets.test_ms("12345", ms)
     left:  {:ok, "12345"}
     right: {:error, [error: 'Function binary_part/3 does_not_exist.']}
     stacktrace:
       test/ex2ms_test.exs:328: (test)

Which seemingly means that :ets.test_ms cannot lookup erlang:binary_part/3 properly. Looking at https://github.com/erlang/otp/blob/master/erts/emulator/beam/bif.tab it appears that it's defined as ubif erlang:binary_part/3 and also as bif binary:part/3 binary_binary_part3. I'm struggling to understand why it's failing to lookup the BIF here - I tried with other ubif definitions, but they seem to work, like abs/1.

Any ideas? I was hoping to put up a PR

Thanks,

JD

[ericmj]

Sorry, I don't know why it doesn't work. I would suggest checking with OTP devs why this doesn't seem to work as expected.

[jdcumpson]

Ok, sounds good. It was worth a shot. I'll try to follow up there. I'll use this issue as reference.