You're seeing just the function failed, go back to Ergo.Meta module for more information.
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failed(parser, fail_fn, opts \\ [])

The failed parser is a combinator that invokes a parser and if the parser fails runs the given function on the resulting context. This can be used to output additional debugging information where failure was unexpected.


iex> alias Ergo.Parser
iex> import Ergo.Meta
iex> failing_parser =, fn ctx -> %{ctx | status: {:error, :unfathomable_error}} end)
iex> parser = failed(failing_parser, fn _ctx -> send(self(), :failed) end)
iex> Ergo.parse(parser, "")
iex> assert_received :failed