First week future learn assignment

first_assignment.erl

-module(first_assignment).
-export([perimeter/1, area/1, enclosing/1, bits/1, tbits/1]).

%%%%%%%%%%%%%%%%%%%%%
% shapes
%%%%%%%%%%%%%%%%%%%%%

% all shapes are represented by one point and parameters
% {rectangle, {x, y}, {width, height}}
% {circle, {x, y}, radius}
% triangle is point and two sides + angle between them
% {triangle, {x, y}, {width, height, angle}}

perimeter({rectangle, {_,_}, {W, H}}) ->
  (2*W)+(2*H);
perimeter({circle, {_,_}, R}) ->
  2 * math:pi() * R;
perimeter({triangle, {_,_}, {A, B, AB}}) ->
  triangle_third_side(A, B, AB) + A + B.

area({rectangle, {_,_}, {W, H}}) ->
  W*H;
area({circle, {_,_}, R}) ->
  math:pi() * R * R;
area({triangle, {_,_}, {A, B, AB}}) ->
  (A * triangle_height(B, AB)) / 2.

enclosing({rectangle, {X, Y}, {W, H}}) ->
  bounding_box(X, Y, (X + W), (Y + H));
enclosing({circle, {X, Y}, R}) ->
  bounding_box((X - R), (Y - R), (X + R), (Y + R));
enclosing({triangle, {X, Y}, {A, B, AB}}) ->
  bounding_box(X, Y, (X + max(A, B)), (Y + triangle_height(min(A,B), AB))).

% Helper functions
triangle_third_side(A, B, AB) ->
  math:sqrt(A * A + B * B - 2 * A * B * math:cos(rad(AB))).

triangle_height(Side, Angle) ->
  Side * math:sin(rad(Angle)).

rad(D) ->
  D * math:pi() / 180.

bounding_box(X1, Y1, X2, Y2) ->
  {{min(X1, X2), min(Y1, Y2)}, {max(X1, X2), max(Y1, Y2)}}.


%%%%%%%%%%%%%%%%%%%%%
% bits
%%%%%%%%%%%%%%%%%%%%%

bits(0) -> 0;
bits(N) ->
  bit(N) + bits(N div 2).

% tail version
tbits(N) -> tbits(N, 0).
tbits(1, A) -> A + 1;
tbits(N, A) ->
  tbits(N div 2, A + bit(N)).

% HELPERS
bit(N) when N rem 2 == 0 -> 0;
bit(_) -> 1.