FutureLearn — Functional Programming in Erlang — Week 1

mwpastore_week1.erl

-module(mwpastore_week1).
-export([area/1, perimeter/1, enclose/1, bits/1]).

area({square, L}) ->
  L * L;
area({rectangle, H, W}) ->
  H * W;
area({circle, R}) ->
  math:pi() * R * R;
area({triangle, A, B, C}) ->
  S = (A + B + C) / 2,
  math:sqrt(S * (S - A) * (S - B) * (S - C)).

perimeter({square, L}) ->
  4 * L;
perimeter({rectangle, H, W}) ->
  2 * H + 2 * W;
perimeter({circle, R}) ->
  2 * math:pi() * R;
perimeter({triangle, A, B, C}) ->
  A + B + C.

enclose({square, L}) ->
  {rectangle, L, L};
enclose({rectangle, H, W}) ->
  {rectangle, H, W};
enclose({circle, R}) ->
  {rectangle, 2 * R, 2 * R};
enclose({triangle, A, B, C}) ->
  W = max(A, max(B, C)), % take the longest side as the base of the triangle
  H = 2 * area({triangle, A, B, C}) / W, % find the height using the area
  {rectangle, H, W}.

bits(N) when N >= 0 ->
  bits(N, 0);
bits(N) ->
  bits(-N, 1). % count the sign bit :)

% Brian Kernighan's algorithm
bits(0, C) -> C;
bits(N, C) ->
  bits(N band (N - 1), C + 1).