Compilation errors with bitstring spec

test.erl

 -module(test).                        
 -compile([export_all]).               
                                       
 -spec foo(<<_:32, _:_*8>>) -> list. 
 foo(<<X:32, Y/binary>>) -> [X, Y].    

test.exs

 defmodule Test do                                
   @spec foo(<<_ :: 32, _ :: _ * 8>>) :: list   
   def foo(<<x :: 32, y :: binary>>), do: [x, y]  
 end                                              
 
 """
 $ elixirc test.exs 

== Compilation error on file test.exs ==
** (CompileError) test.exs:2: type '*'(_,_) undefined
    (stdlib) lists.erl:1336: :lists.foreach/2
    (stdlib) erl_eval.erl:657: :erl_eval.do_apply/6
 """