Ergo.Combinators.lookahead

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

lookahead(parser, opts \\ [])

The lookahead parser accepts a parser and matches it but does not update the context when it succeeds.

Example

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

iex> alias Ergo.Context
iex> import Ergo.{Combinators, Terminals}
iex> parser = lookahead(literal("Helga"))
iex> Ergo.parse(parser, "Hello World")
%Context{status: {:error, :lookahead_fail}, ast: [?l, ?e, ?H], char: ?l, index: 3, col: 4, input: "lo World"}