✨Erlang

fac(0) -> 1; % If 0, then return 1, otherwise (note the semicolon; meaning 'else') fac(N) when N > 0, is_integer(N) -> N * fac(N-1). % Recursively determine, then return the result % (note the period. meaning 'endif' or 'function end') %% This function will crash if anything other than a nonnegative integer is given. %% It illustrates the "Let it crash" philosophy of Erlang.

%% The export statement contains a list of all those functions that form %% the module's public API. In this case, this module exposes a single %% function called fib that takes 1 argument (I.E. has an arity of 1) %% The general syntax for -export is a list containing the name and %% arity of each public function -export([fib/1]).

%% --------------------------------------------------------------------- %% Public API %% ---------------------------------------------------------------------

%% Handle cases in which fib/1 receives specific values %% The order in which these function signatures are declared is a vital %% part of this module's functionality

%% If fib/1 is passed precisely the integer 0, then return 0 fib(0) -> 0;

%% If fib/1 receives a negative number, then return the atom err_neg_val %% Normally, such defensive coding is discouraged due to Erlang's 'Let %% it Crash' philosophy; however, in this case we should explicitly %% prevent a situation that will crash Erlang's runtime engine fib(N) when N < 0 -> err_neg_val;

%% If fib/1 is passed an integer less than 3, then return 1 %% The preceding two function signatures handle all cases where N < 1, %% so this function signature handles cases where N = 1 or N = 2 fib(N) when N < 3 -> 1;

%% For all other values, call the private function fib_int/3 to perform %% the calculation fib(N) -> fib_int(N, 0, 1).

%% --------------------------------------------------------------------- %% Private API %% ---------------------------------------------------------------------

%% If fibint/3 receives a 1 as its first argument, then we're done, so %% return the value in argument B. Since we are not interested in the %% value of the second argument, we denote this using to indicate a %% "don't care" value fibint(1, , B) -> B;

%% For all other argument combinations, recursively call fib_int/3 %% where each call does the following: %% - decrement counter N %% - Take the previous fibonacci value in argument B and pass it as %% argument A %% - Calculate the value of the current fibonacci number and pass it %% as argument B fib_int(N, A, B) -> fib_int(N-1, B, A+B).

fib(0) -> 0; fib(N) when N < 0 -> err_neg_val; fib(N) when N < 3 -> 1; fib(N) -> fib_int(N, 0, 1).

fibint(1, , B) -> B; fib_int(N, A, B) -> fib_int(N-1, B, A+B).

qsort([]) -> []; % If the list [] is empty, return an empty list (nothing to sort) qsort([Pivot|Rest]) -> % Compose recursively a list with 'Front' for all elements that should be before 'Pivot' % then 'Pivot' then 'Back' for all elements that should be after 'Pivot' qsort([Front || Front <- Rest, Front < Pivot]) ++ [Pivot] ++ qsort([Back || Back <- Rest, Back >= Pivot]).