FutureLearn functional programming erlang assignment 1

assignment.erl

-module(assignment).
-export([area/1, perimeter/1, enclose/1, bits/1, bits_tail/1]).

area({A,B,C}) ->
  S = (A+B+C)/2,
  math:sqrt(S*(S-A)*(S-B)*(S-C));

area({A,B}) ->
  A*B.

perimeter({A,B,C}) ->
  A+B+C;

perimeter({A,B}) ->
  2*(A+B).

% assumes A is the base of the triangle
enclose({A,B,C} = Triangle) ->
  Height = area(Triangle) * 2 / A,
  {A, Height}.


bits(N) when N > 0 ->
  N rem 2 + bits(N div 2);
bits(_N) -> 0.

bits_tail(N) -> bits_tail(N, 0).
bits_tail(N, Acc) when N > 0 ->
  bits_tail(N div 2, Acc + (N rem 2));
bits_tail(_N, Acc) -> Acc.