In Erlang, one would usually pass atoms like 'with_gain' or 'without_gain', and substitute default values with arity-overloading: e.g. there would be two calc_f

In Erlang, one would usually pass atoms like 'with_gain' or 'without_gain', and substitute default values with arity-overloading: e.g. there would be two calc_formula functions, one with 2 arguments and one with 3 arguments, and the 2-argument one would simply call the 3-argument with the last parameter set to 'with_gain'. And in case of really large number of parameters, one would generally pass either a map or (in older code) a proplist: #{is_gain => true, other_param => 42, ...} or [{is_gain, true}, {other_param, 42}, ...]. There is no beautiful syntax for destructuring all that stuff with default values, unfortunately.