Functional Programming in Erlang - 2.6 Practice

prac206.erl

-module(prac206).
-export([product/1, maximum/1, product1/1, maximum1/1]).

product(Xs) ->
    product(Xs,1).

% The product of an empty list is usually taken to be 1: why?
% Identity property of  Multiplication:
% Multiplication of any number with 1 results in the original number

product([],P) -> P;
product([X|Xs],P) -> product(Xs,X*P).

product1([]) -> 1;
product1([X|Xs]) -> X * product1(Xs).

maximum([X|Xs]) ->
   maximum(Xs,X).

maximum([],Max) -> Max;
maximum([X|Xs],Y) when X > Y -> maximum(Xs,X);
maximum([_|Xs],Max) -> maximum(Xs,Max).

maximum1([Max]) -> Max;
maximum1([X|Xs]) ->
    Max = maximum1(Xs),
    if
        Max > X -> Max;
        true -> X
    end.