Ergo.Combinators.optional

You're seeing just the function optional, go back to Ergo.Combinators module for more information.
Link to this function

optional(parser, opts \\ [])

Examples

iex> alias Ergo.{Context, Terminals, Combinators}
iex> context = Context.new("Hello World")
iex> parser = Combinators.optional(Terminals.literal("Hello"))
iex> parser.(context)
%Context{status: :ok, ast: "Hello", input: " World", index: 5, col: 6, char: ?o}

iex> alias Ergo.{Context, Terminals, Combinators}
iex> context = Context.new(" World")
iex> parser = Combinators.optional(Terminals.literal("Hello"))
iex> parser.(context)
%Context{status: :ok, ast: nil, input: " World", index: 0, col: 1, char: 0}