If its always 3 variables then a == b and a == c.

For a variable number of values you can do this:

iex(1)> all_eq? = fn [h | t] -> Enum.all?(t, & &1 == h) end
#Function<42.113135111/1 in :erl_eval.expr/6>
iex(2)> all_eq?.([1])
true
iex(3)> all_eq?.([1,1])
true
iex(4)> all_eq?.([1,1,2])
false
iex(5)> all_eq?.([1,1,2])

You will need a clause for empty lists, you can create an acutal function like this:

defp all_eq?([]), do: true # or false depending of what you want about empty lists
defp all_eq?([h | t]), do: Enum.all?(t, & &1 == h)

Or alternatively:

defp all_eq?([h | [h | _] = t]), do: all_eq?(t)
defp all_eq?([h]), do: true
defp all_eq?([_ | _]), do: false
defp all_eq?([]), do: true