Functional Programming in Erlang, unit 1.15 https://www.futurelearn.com/courses/functional-programming-erlang/3/steps/488092/

one15.erl

-module(one15).
-export([xOr1/2, xOr2/2, xOr3/2, xOr4/2, xOr5/2, xOr6/2, xOr7/2, maxThree/3, howManyEqual/3, howManyEqual2/3, howManyEqual3/3]).

%% first example given by Prof. Thompson
xOr1(true, false) ->
    true;
xOr1(false, true) ->
    true;
xOr1(_,_) ->
    false.

% second example given by Prof. Thompson
xOr2(X, X) ->
    false;
xOr2(_, _) ->
    true.


% Give at least three other examples:

xOr3(X, Y) ->
    X =/= Y.

xOr4(X, Y) ->
    not(X == Y).

xOr5(true, Y) ->
    not(Y);
xOr5(false, Y) ->
    Y.

xOr6(X, Y) ->
    X and not(Y) or Y and not(X).

xOr7(X, false) ->
    X;
xOr7(false, Y) ->
    Y.

%% Maximum of three

%% Give a definition of the function maxThree which takes three integers and
%% returns the maximum of the three. You can use the max function, which gives
%% the maximum of two numbers, in writing your definition.
%% maxThree(34,25,36) = 36

maxThree(X, Y, Z) ->
    max(max(X, Y), Z).

%% Give a definition of the function howManyEqual which takes three integers and
%% returns an integer, counting how many of its three arguments are equal, so
%% that:

%% howManyEqual(34,25,36) = 0
%% howManyEqual(34,25,34) = 2
%% howManyEqual(34,34,34) = 3

%% This implementation will fail while comparing ints and floats
howManyEqual(X, X, X) ->
    3;
howManyEqual(X, X, _) ->
    2;
howManyEqual(X, _, X) ->
    2;
howManyEqual(_, X, X) ->
    2;
howManyEqual(_, _, _) ->
    0.

%% one approach is using guards
howManyEqual2(X, Y, Z) when (X == Y) and (Y == Z) ->
    3;
howManyEqual2(X, Y, Z) when (X == Y) or (X == Z) or (Y == Z)->
    2;
howManyEqual2(_, _, _) ->
    0.

%% another approach could be to explicitely force the conversion of the
%% arguments to float prior to calling howManyEqual
howManyEqual3(X, Y, Z) ->
    howManyEqual(float(X), float(Y), float(Z)).