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


A ctx: function should be passed & return the whole context. It takes precendence over an ast: function that receives and returns a modified AST. Otherwise the identity function is returned.


iex> alias Ergo.Context
iex> import Ergo.Combinators
iex> f = mapping_fn(ctx: fn _ -> :kazam end)
iex> assert :kazam = f.(%Context{})