Calculate continuous periods in a sorted list of periods

periods.erl

-module(periods).
-export([get_periods/1, dummy_data/0]).

%% Dummy data for demonstration purposes
dummy_data() -> [{1, 3}, {2, 10}, {10, 11}, {20, 23}, {21, 23}, {21, 23}, {50, 51}].

%% Returns a list of continuous periods within a sorted list of periods
%% i.e. [{1,4},{3,5},{6,7}] -> [{6,7},{1,5}]
%% This was largely written to demonstrate how to solve a problem functionally to my boyfriend
get_periods(Periods, Period, []) ->
        [Period | Periods];
get_periods(Periods, null, [Period | Tail]) ->
        get_periods(Periods, Period, Tail);
get_periods(Periods, {PeriodStart, PeriodEnd}, [{Start, End} | Tail]) when Start =< PeriodEnd ->
        get_periods(Periods, {PeriodStart, End}, Tail);
get_periods(Periods, CurPeriod, Remaining) ->
        get_periods([CurPeriod | Periods], null, Remaining).

get_periods(Data) ->
        get_periods([], null, Data).