Practice patterns (1.15)

patterns.erl

%% @doc Practice patterns (1.15)

-module(patterns).
-export([x_or_1/2, x_or_2/2, x_or_3/2, max/2, max_three/3, how_many_equal/3, test/0]).

%% @doc Give three "exclusive ors"

x_or_1(X, Y) ->
    X =/= Y.

test_x_or_1() ->
    true = patterns:x_or_1(true, false),
    true = patterns:x_or_1(false, true),
    false = patterns:x_or_1(false, false),
    false = patterns:x_or_1(true, true),
    ok.

x_or_2(X, Y) ->
    not X == Y.

test_x_or_2() ->
    true = patterns:x_or_2(true, false),
    true = patterns:x_or_2(false, true),
    false = patterns:x_or_2(false, false),
    false = patterns:x_or_2(true, true),
    ok.

x_or_3(X, Y) ->
    X_and_NY = X and (not Y),
    Y_and_NX = Y and (not X),
    X_and_NY or Y_and_NX.

test_x_or_3() ->
    true = patterns:x_or_3(true, false),
    true = patterns:x_or_3(false, true),
    false = patterns:x_or_3(false, false),
    false = patterns:x_or_3(true, true),
    ok.

select(true, X, _) -> X;
select(false, _, Y) -> Y.

%% @doc Give maximum of two numbers

max(X, Y) ->
    First_wins = X > Y,
    select(First_wins, X, Y).

test_max() ->
    A = 2,
    B = 3,
    C = 20,
    B = patterns:max(A, B),
    C = patterns:max(C, B),
    ok.

%% @doc Give maximum of three numbers

max_three(X, Y, Z) ->
    A = patterns:max(X, Y),
    patterns:max(A, Z).

test_max_three() ->
    36 = patterns:max_three(34, 25, 36),
    100 = patterns:max_three(100, 25, 36),
    ok.

%% @doc Count how many of three arguments are equal

how_many_equal(X, X, X) ->
    3;
how_many_equal(X, X, _) ->
    2;
how_many_equal(X, _, X) ->
    2;
how_many_equal(_, X, X) ->
    2;
how_many_equal(_, _, _) ->
    0.

test_how_many_equal() ->
    A = 34,
    B = 35,
    C = 36,
    0 = patterns:how_many_equal(A, B, C),
    2 = patterns:how_many_equal(A, A, B),
    3 = patterns:how_many_equal(A, A, A),
    ok.

%% @doc test functions: x_ors, max, max_three, and how_many_equal

test() ->
    ok = test_x_or_1(),
    ok = test_x_or_2(),
    ok = test_x_or_3(),
    ok = test_max(),
    ok = test_max_three(),
    ok = test_how_many_equal(),
    ok.

Awesome!!

Thanks for kind words and very informative comments on idiomatic Erlang during the course.