Enum.reject
You're seeing just the function
reject, go back to Enum module for more information.
Specs
reject(t(), (element() -> as_boolean(term()))) :: list()
Returns a list of elements in enumerable excluding those for which the function fun returns
a truthy value.
See also filter/2.
Examples
iex> Enum.reject([1, 2, 3], fn x -> rem(x, 2) == 0 end)
[1, 3]