w2list.erl

-module(w2list).
-export([t_product/1, product/1, t_maximum/1, maximum/1]).

% t_ prefix means tail recursion implementation.

t_product(L) ->
    t_product(L, 1).
t_product([], P) ->
    P;
t_product([H|T], A) when is_number(H) ->
    t_product(T, H * A).

product([]) ->
    1;
product([H|T]) when is_number(H) ->
    H  * product(T).

% No magic maximum value like an infinity
% Maximum of empty list is an empty list
%
t_maximum([]) ->
    [];
t_maximum(L) ->
    t_maximum(L, hd(L)).
t_maximum([], M) ->
    M;
t_maximum([_H|T], A) ->
    case T of
        [] -> A;
        _ -> t_maximum(T, max(A, hd(T)))
    end.

maximum([]) -> [];
maximum([A]) -> A;
maximum([H|T]) ->
    max(H, maximum(T)).

Another version of t_maximum

t_maximum([]) -> [];
t_maximum([X | Xs]) -> t_maximum(Xs, X).

t_maximum([], Max) -> Max;
t_maximum([X | Xs], Max) -> t_maximum(Xs, max(Max, X)).

@hsinger,

I like the way you used the first element of the list as the Max. I used 0, and now I realize my algorithm was wrong: if all the numbers in the list were negative, my starting value of 0 would end up being the result--which would be wrong. I need better tests!

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