Elixir default parameters for named functions with multiple clauses
default-parameters, elixir
Solution
Actually, `def sum([], total \\ 0), do: total` will define a function clause that looks like `def sum(list), do: sum(list, 0)`. So I can definitely see your confusion. I will guarantee we emit a warning for such cases in future releases. Thank you!
Problem
I have trouble understanding how default parameters interact with multiple clauses in named functions. It boils down to, why does the following snippet work? ``` defmodule Lists do def sum([], total \\ 0), do: total def sum([h|t], total), do: h + sum(t, total) end ``` From my understanding this gets expanded by the compiler into: ``` defmodule Lists do def sum([]), do: sum([], 0) def sum([], total), do: total def sum([h|t], total), do: h + sum(t, total) end ``` So I would expect the following to happen: ``` iex(1)> Lists.sum [1,2,3,4] ** (FunctionClauseError) no function clause matching in Lists.sum/1 ``` instead it works: ``` iex(1)> Lists.sum [1,2,3,4] 10 ``` Using Elixir 0.12.4.