When I try to compile Elixir I get 'Uncaught error in rebar_core'

What operating system are you running and how did you install erlang?

Fedora distro using dnf package manger

Which version is it? Please copy and paste the headline you get when starting erl. You can leave it afterwards by entering q()..

If it is an OTP release older than 18 should use the erlang version provided by erlang solutions.

Erlang/OTP 19 [erts-8.3.3] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V8.3.3  (abort with ^G)

when I try to add the package from erlang solutions on Fedora Latest using dnf package manger.
Failed to synchronize cache for repo 'erlang-solutions', disabling

while compiling the elixir

==> elixir (compile)
warning: behaviour String.Chars is undefined
  lib/calendar/date.ex:504

warning: behaviour Inspect is undefined
  lib/calendar/date.ex:510

warning: behaviour String.Chars is undefined
  lib/calendar/time.ex:420

warning: behaviour Inspect is undefined
  lib/calendar/time.ex:426

warning: behaviour String.Chars is undefined
  lib/calendar/naive_datetime.ex:648

warning: behaviour Inspect is undefined
  lib/calendar/naive_datetime.ex:655

warning: behaviour String.Chars is undefined
  lib/calendar/datetime.ex:473

Compiling lib/agent/server.ex (it's taking more than 5s)
warning: use Dict is deprecated, use the Map module for working with maps or the Keyword module for working with keyword lists
  lib/hash_dict.ex:11

Hmmm… Dunno why the esl-repo is failing, I’m not using Fedora, only wanted to make sure that you have a recent enough version of erlang…

Anyway, your compilation of elixir seems to have suceeded. I do not see any errors in your log, but warnings only.