This is an issue of using
Erlang/OTP 23 and
Elixir 1.9.4 simultaneously.
Elixir 1.9 is older than OTP 23, but elixir fully leverages OTP, so it relies on some warnings/messages coming from erlang compiler during compilation.
That said, downgrading OTP to the version
Elixir 1.9 is aware of (21 would be fine, I believe,) or upgrading Elixir to the recent
1.11.1 would fix the issue producing fancy
== Compilation error in file /tmp/test.ex == ** (CompileError) /tmp/test.ex:3: undefined function do_addition_problems/1 (elixir 1.11.1) src/elixir_locals.erl:114: anonymous fn/3 in :elixir_locals.ensure_no_undefined_local/3 (stdlib 3.13.2) erl_eval.erl:680: :erl_eval.do_apply/6
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