Disclaimer: I'm a maintainer but the next Dialyxir release makes a major improvement on this, thanks to contributions from Andrew Summers. He wrote a parser for the Erlangified term strings and uses the Elixir (1.6) pretty printer to print all the terms the way Elixir would. We're still fine-tuning the error messages and explanations but there is an RC on hex[0] - give it a spin if you haven't yet.

[0] https://hex.pm/packages/dialyxir/1.0.0-rc.3

You should try Dialyxir 1.0.0-rc3! The error reporting is vastly improved by a GSoC student.

Now you can get errors like this:

  ________________________________________________________________________________
  apps/activity_feed/lib/activity_feed/push_notification_listener.ex:10:callback_type_mismatch
  Callback mismatch for @callback push/2 in ActivityFeed.ListenerBehaviour behaviour.
  
  Expected type:
  {:error, _} | {:ok, _}
  
  Actual type:
  :ok
  ________________________________________________________________________________
  apps/activity_feed/lib/activity_feed/push_notification_listener.ex:24:pattern_match
  The pattern
  _ = {:error, _}
  
  can never match the type
  :error | :ok