list_functions.erl

-module(list_functions).
-export([product/1,maximum/1,product_notail/1,maximum_notail/1]).
-export([product_test/0,maximum_test/0,product_notail_test/0,maximum_notail_test/0]).

%% Product %%%

product([]) -> 1;
product([A|B]) -> product([A|B], 1).

product([], P) -> P;
product([A|B], P) -> product(B, A*P).

product_test() ->
  1 = product([]),
  2 = product([2]),
  6 = product([2,3]),
  42 = product([2,7,3,1]),
  -2 = product([2,-1]),
  0 = product([3,7,0,21]),
  passed.

%% Maximum %%%

maximum([A|[]]) -> A;
maximum([A|B]) -> maximum(B,A).

maximum([], Max) -> Max;
maximum([A|L], Max) ->
  maximum(L, max(A, Max)).

maximum_test() ->
  7 = maximum([7]),
  1 = maximum([0, 1]),
  7 = maximum([5, 3, 7]),
  -2 = maximum([-7, -3, -2]),
  passed.

%% Product non tail-recursive %%%

product_notail([]) -> 1;
product_notail([A|[]]) -> A;
product_notail([A|[B|T]]) -> A*B*product(T).

product_notail_test() ->
  1 = product_notail([]),
  2 = product_notail([2]),
  6 = product_notail([2,3]),
  42 = product_notail([2,7,3,1]),
  -2 = product_notail([2,-1]),
  0 = product_notail([7,3,0,21]),
  passed.

%% Maximum non tail-recursive %%%

maximum_notail([A|[]]) -> A;
maximum_notail([A,B]) -> max(A,B);
maximum_notail([A|B]) -> max(A, maximum(B)).

maximum_notail_test() ->
  7 = maximum_notail([7]),
  1 = maximum_notail([0, 1]),
  7 = maximum_notail([5, 3, 7]),
  -2 = maximum_notail([-7, -3, -2]),
  passed.

Well done!