Elixir Function definition without body error

Questions / Help
1

I am reading a book and found the below example.

defmodule Params do
  def func(p1, p2 \\ 2)
  def func(p1, p2) when is_list(p1) do
    IO.inspect "You said #{p2} with a list"
  end

    def func(p1, p2) do
    IO.inspect "You passed in #{p1} and #{p2}"
  end
end

And I ran it like:

mm$ iex params.exs
Erlang/OTP 21 [erts-10.0.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]

Interactive Elixir (1.6.6) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Params.func 1
"You passed in 1 and 2"
"You passed in 1 and 2"
iex(2)> Params.func 1, 5
"You passed in 1 and 5"
"You passed in 1 and 5"
iex(3)> Params.func [99]
"You said 2 with a list"
"You said 2 with a list"
iex(4)>

I am not getting why there is function definition without any body in it? Can anyone explain why is that needed? If comment out # def func(p1, p2 \\ 2), still the program works as expected.

2

When you comment out the body-less clause, then func(1) should fail, as there is nothing anymore that specifies the default value for the second argument.

In general it has to be used when having default values for arguments and multiple clauses at all.

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