Elixir anonymous function recursion

gistfile1.txt

calculate_bill = fn
  {:item, price} -> price
  [h|t] -> calculate_bill.(h) + calculate_bill.(t)
end

calculate_bill.([{:item, 20}, {:item, 10}])
calculate_bill.({:item, 35})
# It should also work with a list of more than two elements:
calculate_bill.([{:item, 20}, {:item, 10}, {:item, 35}])

iex(17)> calculate_bill.([{:item, 20}, {:item, 10}])
** (UndefinedFunctionError) undefined function: IEx.Helpers.calculate_bill/1
    IEx.Helpers.calculate_bill({:item, 10})
    erl_eval.erl:569: :erl_eval.do_apply/6
    erl_eval.erl:395: :erl_eval.expr/5
    erl_eval.erl:396: :erl_eval.expr/5
    src/elixir.erl:147: :elixir.eval_forms/3

iex(17)> calculate_bill.({:item, 35})
35